                         Docket No. 102372.


                              IN THE
                      SUPREME COURT
                                 OF
                 THE STATE OF ILLINOIS




THE PEOPLE OF THE STATE OF ILLINOIS, Appellee, v.
           JOANNE McKOWN, Appellant.



                  Opinion filed February 19, 2010.



   JUSTICE GARMAN delivered the judgment of the court, with
opinion.
   Chief Justice Fitzgerald and Justices Freeman, Thomas, Kilbride,
Karmeier, and Burke concurred in the judgment and opinion.



                              OPINION

    Following a bench trial in the circuit court of Peoria County,
defendant was convicted of two counts of aggravated driving under
the influence of alcohol (DUI) (625 ILCS 5/11–501(d)(1)(C) (West
2006)), and other offenses. The appellate court affirmed (People v.
McKown, No. 3–04–0433 (2006) (unpublished order under Supreme
Court Rule 23)), and this court granted her petition for leave to
appeal. The single issue raised in her petition was whether she was
entitled to a hearing pursuant to the rule of Frye v. United States, 293
F. 1013 (D.C. Cir. 1923), before evidence of her performance on a
horizontal gaze nystagmus (HGN) test could be admitted. We held
that the trial court and the appellate court erred in taking judicial
notice that the HGN test is generally accepted as an indicator of
alcohol impairment and remanded to the trial court with instructions
to conduct a Frye hearing. People v. McKown, 226 Ill. 2d 245, 248
(2007) (McKown I). We retained jurisdiction and now review the trial
court’s judgment on that issue.

                             BACKGROUND
     Under the rule of Frye, scientific evidence is admissible at trial
only “if the methodology or scientific principle upon which the opinion
is based is ‘sufficiently established to have gained general acceptance
in the particular field in which it belongs.’ ” In re Commitment of
Simons, 213 Ill. 2d 523, 529-30 (2004), quoting Frye, 293 F. at 1014.
Further, the Frye test is necessary only if the scientific principle,
technique or test offered by the expert to support his or her conclusion
is “new” or “novel.” See People v. Basler, 193 Ill. 2d 545, 550-51
(2000).
     We held in McKown I that “[b]ecause the results of an HGN test
require expert interpretation” by a trained police officer, “the results
of HGN testing are scientific evidence.” McKown I, 226 Ill. 2d at 257.
We further held that, despite its use by police officers for many years,
“the methodology of HGN testing is novel for purposes of Frye.”
McKown I, 226 Ill. 2d at 258. Thus, a Frye hearing was necessary “to
determine if the HGN test has achieved general acceptance as a
reliable indicator of alcohol impairment.”1 McKown I, 226 Ill. 2d at
257. Finally, although we noted that it was appropriate in some
circumstances for a trial court to resolve the question of general
acceptance via judicial notice (McKown I, 226 Ill. 2d at 254), this

   1
     We note that this statement in McKown I was not intended to graft an
additional element of reliability onto the Frye test. As we observed in
Donaldson, “[t]he trial court is not required to conduct a two-part inquiry
into both the reliability of the methodology and its general acceptance.” The
question of reliability is “subsumed by the inquiry into its general acceptance
in the scientific community.” Donaldson v. Central Illinois Public Service
Co., 199 Ill. 2d 63, 81 (2002). See also In re Commitment of Sandry, 367
Ill. App. 3d 949, 966 (2006) (“once it is determined that a methodology is
generally accepted, it follows that it has achieved a sufficient degree of
reliability and validity to cross the threshold of admissibility”).

                                     -2-
particular issue could not be resolved “on judicial notice alone”
(McKown I, 226 Ill. 2d at 275). We remanded the matter to the trial
court for a Frye hearing to determine whether HGN testing is
generally accepted in the particular scientific field to which it belongs
as an indicator of alcohol impairment and to make findings of fact and
conclusions of law as to this question. McKown I, 226 Ill. 2d at 276-
77.
    Nystagmus is “an involuntary, rapid, rhythmic movement of the
eyeball, which may be horizontal, vertical, rotatory, or mixed, i.e., of
two varieties.” Dorland’s Illustrated Medical Dictionary 1296 (30th
ed. 2003). The medical dictionary lists 45 types of nystagmus. For
example, ataxic nystagmus is unilateral and occurs in individuals with
multiple sclerosis. Dorland’s Illustrated Medical Dictionary 1296
(30th ed. 2003). Congenital nystagmus “may be caused by or
associated with optic atrophy, coloboma, albinism, bilateral macular
lesions, congenital cataract, severe astigmatism, and glaucoma.”
Dorland’s Illustrated Medical Dictionary 1296 (30th ed. 2003). Gaze
nystagmus, which is at issue in the present case, is “made apparent by
looking to the right or to the left,” as opposed to fixation nystagmus,
“which appears only on gazing fixedly at an object,” or latent
nystagmus, “which occurs only when one eye is covered.” Dorland’s
Illustrated Medical Dictionary 1296 (30th ed. 2003).
    The methodology employed by law enforcement officers for
conducting an HGN testing as a part of field-sobriety testing is
explained in detail in our earlier opinion. In brief, the officer first
questions the subject to determine whether he or she has any medical
condition or is taking any medication that might affect the results of
the test. If not, the officer performs a preliminary test to determine
whether the pupils of the subject’s eyes are of equal size and whether
the eyes “track” equally as an object is moved, at eye level, from side
to side. If so, the HGN test itself is performed. The officer looks for
three “clues,” assessing each eye separately. The three clues are lack
of smooth pursuit, distinct nystagmus at maximum deviation, and the
onset of nystagmus at an angle less than 45 degrees. One point is
assigned for each clue that is present in either eye. Thus, the maximum
score is six, which would indicate all three clues present in both eyes.
A score of four or more is considered “failing” and indicative of
alcohol impairment. McKown I, 226 Ill. 2d at 249-50.

                                  -3-
                              The Evidence
    The Frye hearing was held over the course of four dates between
March 2007 and April 2008. The State presented the testimony of Dr.
Carl Citek, Master Sergeant Antonio Lebron, Dr. Zenon Zuk, and
Thomas Page. Defendant presented the testimony of Dr. Joseph
Citron, Dr. Ronald Henson, and Dr. Steven Reubenzner. In addition,
each party submitted numerous journal articles and other writings in
support of its position. Finally, each party submitted a trial brief
arguing for certain findings of fact and conclusions of law.
    Although the State had the burden on remand of demonstrating
that the HGN test meets the Frye standard (People v. Basler, 193 Ill.
2d 545, 551 (2000)), the presentation of evidence began with the
testimony of a witness called by the defendant.
    Dr. Joseph Citron testified that he is a board-certified
ophthalmologist who received his clinical training at the Mayo Clinic
in Rochester, Minnesota. He practices in Atlanta, Georgia, and has
over 30 years experience in emergency medical care, including the
care of intoxicated patients. In 1999, he completed the National
Highway Transportation Safety Administration (NHTSA) training
course in field-sobriety testing, which included training in the HGN
test. He has 10 years of experience as an instructor on field-sobriety
testing for the Atlanta police department and other agencies. He also
holds a law degree.
    Citron explained the differences in education and training between
an ophthalmologist and an optometrist, as well as the fact that an
optometrist does not perform surgery or medical diagnosis. He also
explained the meaning of the term “nystagmus,” which he described
as a condition that is “usually pathologic in origin” and “not part of
the normal findings in an individual.” Nystagmus itself is not a
diagnosis; it is merely a description of a certain type of eye movement
that may be caused by many conditions. He was unable to give a
specific number of recognized causes, but agreed with the statement
that the number is at least 39. Citron further testified that once an
individual had consumed sufficient alcohol to “reach the threshold of
central nervous system depression,” he could display nystagmus.
    With regard to the HGN test performed by law enforcement
officers, Citron explained that the test is not performed in the same


                                 -4-
manner as the test a physician would perform during the examination
of a patient. He then explained that the NHTSA, which is a division
of the United States Department of Transportation, has promulgated
standards for performing the HGN test as a field-sobriety test. These
standards must be observed “in the same fashion every time by
everybody” and individual test results would be invalid if the test were
not performed in the “prescribed standardized fashion.” He then made
a presentation regarding the proper procedure for performing the
HGN test.
     Citron testified that based on a “failed” HGN test alone, one could
not form an opinion that the cause of the failure was alcohol. The test
is a “preliminary test.” It is “the beginning of an evaluation, not the
conclusion.” Further, if one offered an opinion that the failure of the
test was caused by alcohol, that opinion would be conjecture or
speculation. Finally, Citron testified that a failed HGN test is a sign
that the subject’s central nervous system (CNS) is depressed. While
the cause of CNS depression might be recent consumption of alcohol,
the failed test is not an indicator of actual impairment due to alcohol.
     On cross-examination by the State, Citron reiterated that HGN
can be an indicator of alcohol consumption and that an officer who
observes a failed HGN test can “put the presence of alcohol as a
central nervous system depressant on a list of possible causes for these
findings.”
     The State’s case began with the testimony of Master Sergeant
Lebron of the Illinois State Police. He holds a bachelor’s degree in law
enforcement administration and, as part of his training to become a
state trooper, received training in the administration of standardized
field-sobriety tests. He testified that he spent 16 years as a patrol
officer. Lebron estimated that over the course of his career, he has
conducted close to 500 DUI investigations. Prior to taking his current
supervisory position, Lebron served as the breath-alcohol section
supervisor at the State Police Academy. In this capacity, he was
responsible for training new recruits in standardized field-sobriety
testing, including administration of the HGN test using the NHTSA
manual. A copy of the manual was introduced into evidence.
     Lebron described conducting workshops at the Academy during
which some volunteers would consume differing amounts of alcohol
and others would be given a placebo as a control. The volunteers

                                  -5-
would take Breathalyzer tests to measure their blood-alcohol levels.
Then the trainees would perform field-sobriety tests on the volunteers.
During theses workshops, he observed that volunteers who had
consumed a sufficient amount of alcohol displayed HGN as well as a
degree of reduced motor skills. He has observed 400 to 500
volunteers being examined in such workshops.
     He then testified that the HGN test, if performed according to the
standardized protocol, is generally accepted in the law enforcement
community as a reliable indicator of impairment due to alcohol. After
a defense objection, he clarified this statement to say that, in his
opinion, a failed HGN test is an indicator that the person has
consumed alcohol.
     On cross-examination, Lebron acknowledged that he has seen
individuals fail all three of the field-sobriety tests when they had
absolutely no alcohol in their systems.
     Dr. Karl Citek, a professor of optometry at Pacific University
College of Optometry in Forest Grove, Oregon, testified for the State.
He is involved in training police officers to perform standardized field-
sobriety tests and has observed these tests being performed in
controlled conditions. On one occasion, he accompanied patrol
officers and performed an HGN test in the field. On questioning by
defense counsel regarding his expert credentials, he acknowledged
that as an optometrist, he was not qualified to diagnose or treat any
of the several dozen conditions that may cause nystagmus.
     After being accepted as an expert witness, Citek testified that
optometrists have a “better feel for the test” than ophthalmologists
because “when nystagmus occurs because of an outside influence ***
visual function is reduced.” He also testified regarding a resolution
adopted in 1993 by the American Optometric Association (AOA)
House of Delegates endorsing the HGN test as a valid and reliable
field-sobriety test. He stated that the resolution was renewed in 2006
and that he agrees with the resolution.
     On cross-examination, Citek acknowledged that lack of smooth
pursuit could be exhibited by a subject with a blood-alcohol
concentration as low as 0.02 and that nystagmus at maximum
deviation could be exhibited by a subject with a blood-alcohol
concentration as low as 0.04. Thus, a subject could be given a “failing


                                  -6-
score” on the HGN test with a blood-alcohol concentration at half the
statutory limit of 0.08 (625 ILCS 5/11–501(a)(1) (West 2006)). Citek
noted, however, that some individuals could be intoxicated at this
level.
     With regard to officer training, Citek acknowledged that an officer
could pass the standard written test following training in field-sobriety
testing by answering 16 of 20 questions correctly and that only four
of the 20 questions relate to HGN testing. Thus, an officer could
answer all questions concerning HGN testing incorrectly and still
receive certification in field-sobriety testing. Citek noted that in
addition to passing the written test, officers must perform HGN tests
at a live workshop to demonstrate proficiency before being certified.
He was unable to answer further questions about the test and the
testing procedure because, although he had read the NHTSA training
manual, he himself had not completed the training.
     On the question of the American Optometric Association
resolution, Citek testified that he was not present at the 1993 annual
meeting at which the resolution was adopted. He did not know if the
resolution was debated prior to being voted upon or how the vote was
taken, by head count or by acclamation.
     The State next presented the testimony of Dr. Zenon Zuk, medical
director of the Los Angeles County/University of Southern California
Employee Health Care System. Zuk was previously employed as staff
physician at the Los Angeles County jail, where he performed more
than 7,000 medical evaluations on arrestees admitted to the jail. These
evaluations included an assessment of whether the arrestee was under
the influence of alcohol or other drugs.
     Zuk testified that, in his opinion, a finding of HGN is generally
accepted in the medical community as an indicator of alcohol-induced
CNS impairment. If he were to observe HGN during the examination
of a patient, he would inquire about the ingestion of drugs and/or
alcohol within in the previous 12 to 24 hours. He stated that he could
not make a diagnosis solely on the basis of HGN, but that the test is
a “linchpin” in determining whether a patient’s CNS is impaired.
     He also testified that police officers can be trained to administer
the test correctly and to observe the presence of HGN. He opined that
the HGN test used by law enforcement is “more rigid,” “more


                                  -7-
formal,” and “more methodical” than the HGN test used by
physicians.
     Zuk stated that there are 35 to 40 different forms of nystagmus
and explained at length how these can be distinguished from HGN. On
cross-examination, however, he acknowledged that nystagmus might
be a symptom of as many as 125 diseases or conditions. He stated on
redirect examination that while these conditions could cause
nystagmus, it would not manifest “in the exact same way as HGN.”
Further, many of the diseases or conditions on this list are rare and
perhaps 80% of them would not be seen by a practicing physician “in
a lifetime of practice.”
     Finally, Zuk acknowledged that the HGN test was originally
validated as a test for estimating a person’s blood-alcohol
concentration, not as a measure of driving impairment.
     Thomas Page testified for the State that he served as a police
officer for 22 years in Detroit and Los Angeles. He has administered
the HGN test in the field and has observed other officers doing so. He
trains police officers and others to perform the test and to interpret the
results. He opined that the test is “universally” accepted within the law
enforcement community as a reliable indicator of alcohol impairment.
     He testified that in his experience, the presence of HGN has
corresponded to the presence of an impairing level of alcohol in the
subject’s system. He did not, however, provide any data in support of
this statement. He acknowledged that he could not speak to the
question of general acceptance of HGN testing within the scientific or
medical communities.
     At the conclusion of the State’s case, the defendant presented her
remaining witnesses.
     Dr. Ronald Henson is a former police officer who was among the
first officers to receive NHTSA training on HGN testing in Illinois.
His doctorate is in the field of applied management and decision
sciences. He has been an instructor on field-sobriety testing at the
Police Training Institute at the University of Illinois and has taught the
physiology and pharmacology of alcohol at Bradley University. He is
familiar with HGN research, having collected papers and articles on
the subject for over 25 years, and he has written and lectured on the
subject.

                                   -8-
     He testified that the test was designed to estimate the subject’s
blood-alcohol concentration , not to reveal impairment, and that it has
not been accepted in the academic community as a reliable indicator
of alcohol impairment because it cannot discriminate between those
who have merely consumed alcohol and those who have consumed
too much.
     He further testified to his opinion that Illinois’ training of police
officers on the subject of field-sobriety testing is inadequate. While the
NHTSA recommends a 24-hour course, Illinois devotes only four to
six hours to the entire three-test battery of field-sobriety tests. Only
one hour is devoted to HGN. Further, the NHTSA-approved written
test contains 20 questions on field-sobriety tests while the Illinois test
contains six or fewer such questions. Illinois does not require that
officers undergo retraining or recertification in field-sobriety testing.
Based on his review of videotapes of actual Illinois arrests, he opined
that only 1 in 100 field HGN tests is properly administered.
     Dr. Steven Rubenzer testified that he is a board-certified forensic
psychologist. He has completed both the NHTSA student course and
its instructor course. He has published several peer-reviewed articles
relating to HGN testing.2 Based on a survey of psychologists that he
conducted, he testified that HGN testing is not generally accepted in
his field as an indicator of intoxication and that there are no academic
studies validating the test as a measure of impairment.
     He pointed to the lack of peer-reviewed literature on the subject
by ophthalmologists and optometrists and to what he described as
flaws in the methodology of the original research study on this subject.
See M. Burns & H. Moskowitz, Psychophysical Tests for DWI
Arrest, DOT HS-802 424, June 1977, U.S. Department of
Transportation, National Highway Traffic Safety Administration. A
later article by Burns stated that a more recent study showed that 20
out of 26 people who failed the test had a blood-alcohol concentration


   2
     Defendant states in her brief that this court “referred to” an article by
this witness in its opinion in McKown I. While this statement is literally true,
we “referred” to the article only as being on her “extensive list of articles that
condemn the reliability of HGN testing.” McKown I, 226 Ill. 2d at 273. We
did not, in any sense, endorse or rely on the article.

                                       -9-
below 0.08, which he described as a false positive error rate of 67%.
He also described a 1981 study showing “interrater reliability” of only
0.66. That is, when the subject was examined by two police officers,
the officers’ judgment of impairment was the same in only two-thirds
of cases. He opined that a interrater reliability coefficient of less than
0.80 rendered the test unreliable.
    On cross-examination, Rubenzer acknowledged that his peer-
reviewed article cited a journal called “Journal of Optometry and the
Law,” which does not exist. He further acknowledged that he has not
conducted any research studies on the HGN test and that he has no
medical training. His survey of psychologists was conducted on-line.
Of 64 board-certified psychologists who responded to his query, 53
stated that they believed that HGN testing was not generally accepted
in their field.

      The Trial Court’s Findings of Fact and Conclusions of Law
     In brief answer, the trial court concluded that “the clinical HGN
test is generally accepted in the scientific world of ophthalmology and
optometry as a reliable (preliminary) indicator of alcohol impairment.”
While acknowledging that the roadside HGN test as performed by law
enforcement officers “has been questioned as to its general acceptance
and reliability,” the trial court noted that the “scientific principle itself
is unquestioned.” In addition, the trial court found that the HGN test,
when properly conducted by a trained police officer, “has been shown
to be a sufficiently reliable component of field-sobriety testing that
assists the police officer in making the decision to arrest and to
formulate an opinion (along with other evidence) of whether a person
is operating a motor vehicle under the influence.”
     At the conclusion of its summary of the evidence presented, the
trial court made five enumerated conclusions of law:
             “1. HGN testing satisfies the Frye standard in Illinois.
             2. HGN testing is but one facet of field sobriety testing
         and is admissible as a factor to be considered by the trier-of-
         fact on the issue of alcohol or drug impairment.
             3. A proper foundation must include that the witness has
         been adequately trained, has conducted testing and assessment
         in accordance with the training, and that he administered the

                                    -10-
       particular test in accordance with his training and proper
       procedures.
           4. [Testimony regarding] HGN testing results should be
       limited to the conclusion that a “failed” test suggests that the
       subject may have consumed alcohol and may [have] be[en]
       under the influence. There should be no attempt to correlate
       the test results with any particular blood-alcohol level or range
       or level of intoxication.
           5. In conjunction with other evidence, HGN may be used
       as a part of the police officer’s opinion that the subject [was]
       under the influence and impaired.” (Emphasis in original.)

                        ISSUES PRESENTED
    Defendant argues that: (1) the HGN test is not a reliable indicator
of impairment due to alcohol and, therefore, does not meet the Frye
standard; (2) even if the HGN test does meet the Frye standard,
admissibility of test results should be limited to showing probable
cause for arrest; (3) if HGN test results are admissible at trial, the
court must strictly enforce standards for performance of the test; (4)
police officers who testify regarding HGN test results are testifying as
expert witnesses and should not be considered qualified unless they
have received extensive training; (5) the trial court’s findings of fact
in the Frye hearing were erroneous; and (6) the HGN test results
should not have been admitted at her trial because the officer did not
properly administer the test.
    The State responds that the HGN test does meet the Frye standard
and that use of this evidence should not be limited to establishing
probable cause. In response to defendant’s third and fourth arguments,
the State argues that this court should adopt the trial court’s
foundational requirements for admissibility. The State also argues that
defendant has forfeited her final argument by failing to raise the issue
in her petition for leave to appeal.

                            ANALYSIS
    At the Frye hearing, the burden was on the State to demonstrate
that HGN testing is generally accepted in the relevant scientific field
as an indicator of alcohol impairment. People v. Miller, 173 Ill. 2d

                                 -11-
167, 187-88 (1996) (proponent of evidence predicated upon a
scientific theory bears the burden of demonstrating that the theory
relied upon by the expert has gained general acceptance in the expert’s
scientific field). We review the trial court’s conclusion that the State
has met this burden de novo. In doing so, we may “consider not only
the trial court record but also, where appropriate, sources outside the
record, including legal and scientific articles, as well as court opinions
from other jurisdictions.” Commitment of Simons, 213 Ill. 2d at 531.
     We note that the various witnesses, although knowledgeable and
experienced, were not altogether objective. Each has a stake of some
sort in the outcome of this debate. Thus, we are guided more by the
points on which they agree than by any points of disagreement.

             Challenge to the Trial Court’s Findings of Fact
     Defendant argues that the findings of fact upon which the trial
court’s conclusion was based are erroneous. She takes particular
exception to the trial court’s uncritical acceptance of the American
Optometric Association’s resolution and its reliance on case law from
other states that predates some of the more current scientific
literature.
     In its written findings of fact, the trial court stated that the “long-
standing resolution of the American Optometric Association declaring
the HGN test ‘to be a scientifically valid and reliable tool for trained
officers to use in field sobriety testing’ is compelling evidence showing
a sufficient consensus in the scientific community to allow HGN
testimony in Illinois courts.”
     The resolution was introduced into evidence via the testimony of
Citek, who, on cross-examination, could provide no background
information regarding the purpose for which it was proposed, the
circumstances under which the resolution was adopted, or the debate,
if any, over the proposal.
     The American Optometric Association is a professional
organization, not a scientific body. Its goals are to set professional
standards, lobby government and other organizations on behalf of the
profession, and to provide leadership for research and education. See
http://www.aoa.org (last visited February 1, 2010). According to
Citek’s testimony, not all members of the profession are members of

                                   -12-
the Association.
     We do not believe that a resolution adopted by the members of a
professional organization can be considered evidence of consensus
among the members of that profession. Of the 36,000 actual members,
it is likely that a fraction were present at the American Optometric
Association House of Delegates in 1993 when this resolution was
adopted and when it was subsequently reaffirmed. The record contains
no information as to the number of members voting for or against the
resolution. Thus, rather than expressing general acceptance, the
resolution expresses the opinion of a relatively small number of
members of the profession.
     Further, the purpose of the American Optometric Association
resolution was to urge doctors of optometry to “become involved as
professional consultants in the use of HGN field sobriety testing.”
Thus, rather than expressing a considered professional opinion on the
science underlying HGN testing, the resolution expressed an interest
in urging members to take advantage of a professional opportunity
being created by the emerging acceptance of HGN testing by law
enforcement agencies.
     Thus, we agree with the defendant on this point and give no
weight whatsoever to the Association’s resolution.
     Each party provided the trial court with journal articles and other
literature in support of its position. The State introduced into evidence
a volume entitled “DWI Detection and Standardized Field Sobriety
Testing” (cited therein as DOT HS 178 R2/06), published by the
NHTSA as a training manual for students participating in training for
field-sobriety testing. Six pages of the volume are devoted to the
subject of nystagmus. The volume outlines a 10-step procedure for
performing a field test for HGN. DOT HS 178 R2/06, at VIII-7.
     The volume also contains a bibliography listing 34 “Scientific
Publications and Research Reports Addressing Nystagmus.” The
actual reports and publications are not included. Given this lack of
content regarding the science underlying HGN field testing, we find
nothing in this volume relevant to the question of general acceptance
in the relevant scientific field.
     The State also submitted journal articles by several of its expert
witnesses and others on the subject of HGN testing and the

                                  -13-
relationship of HGN to impairment due to consumption of alcohol or
other drugs. Many of these publications were prepared under contract
to the NHTSA.
     In addition, the State provided the report of the initial 1977
laboratory study that has served as the basis for the widespread
adoption of HGN field testing. The study was sponsored by the
NHTSA for the purpose of evaluating the field-sobriety tests being
used by police officers at that time, identifying tests that would
provide the most reliable evidence of a blood-alcohol concentration
above the legal limit, and standardizing the procedures for
administering these tests. M. Burns & H. Moskowitz, Psychophysical
Tests for DWI Arrest, DOT HS-802 424, June 1977, U.S. Department
of Transportation, National Highway Traffic Safety Administration.
Ten officers administered a battery of six tests, including HGN, to 238
subjects. Some of the subjects were given alcohol prior to testing;
others were given a placebo. The subjects’ blood-alcohol
concentrations were measured and shown to be in the zero to 0.15
range. The officers were instructed to arrest any subject they believed
to have a blood-alcohol concentration of 0.10 or higher, based on the
results of six field-sobriety tests. They made correct arrest decisions
in 76% of cases. Analysis of the data led to the recommendation that
accuracy could be improved by reducing the number of tests to a
battery of three: one-leg stand, walk-and-turn, and HGN.
     Based on our review of the initial study and the other articles
provided by the State, several themes emerge. First, alcohol and CNS-
depressant drugs affect the neural centers in the brain that control eye
movements, as well as other centers of the brain. Second, HGN
correlates highly with both an elevated blood-alcohol concentration
and with cognitive impairment. Third, an individual may fail the HGN
test by showing 4 or more clues despite a blood-alcohol concentration
below the legal limit for driving. Such a person may or may not be
impaired for driving. Fourth, to be a reliable indicator of alcohol
consumption, HGN field testing must be performed in accordance
with the NHTSA protocol. Fifth, police officers can be trained to
distinguish HGN due to consumption of alcohol or other substances
from some other common forms of nystagmus.
     Defendant argues that the literature she provides is more current
than that relied upon by the State and that, as a result, it calls into

                                 -14-
doubt continued reliance on HGN testing as a field-sobriety test,
despite acceptance by several state courts in the years after the initial
1977 study.
     Several articles written by expert witness Rubenzer are provided.
The articles are descriptive, in that they summarize research done by
others rather than report on independent research. In brief summary,
these articles conclude that HGN testing is being improperly used by
law enforcement. The HGN field test was originally developed by
Burns and others as a tool to screen drivers to determine whether
blood-alcohol concentration testing was justified. The test was not
designed to determine whether the subject is impaired for driving and
its use for this purpose has not been validated by controlled studies.
Further, Rubenzer asserts that the developers of the test, along with
prosecutors, have “oversold” the test.
     Among the other articles provided by defendant, several are taken
from defense-oriented journals and others from the Web sites of
attorneys who engage in DUI defense practice.
     While the points made by Rubenzer and others are worth noting,
we find nothing in the materials provided by defendant to contradict
the five general points listed above that we found supported by the
literature provided by the State.
     In sum, while we agree with defendant that the American
Optometric Association’s resolution is not worthy of consideration
under Frye, we reject her assertion that the trial court’s findings of
fact are erroneous. In any event, because we are engaged in de novo
review, we are not bound by those findings.

                       Relevant Scientific Field
    A review of the evidence presented reveals that HGN is a physical
sign that reveals, among other things, the existence of CNS
depression. Thus, the underlying basic science is the physiology of the
CNS. Practitioners such as neurologists, ophthalmologists, and
optometrists are trained to perform this test in a clinical setting and to
observe the results and, in the case of physicians, to diagnose and treat
conditions that cause nystagmus.
    As noted above, in the 1970s, the NHTSA sponsored research by
psychologist Dr. Marcelline Burns of the Southern California

                                  -15-
Research Institute into the reliability of field-sobriety testing. Based
on her research, which found a correlation between the ingestion of
alcohol and the presence of HGN, law enforcement agencies adopted
this clinical test for use as a field-sobriety test.
    Lebron and Page testified that HGN testing is generally accepted
within the law enforcement community as a field-sobriety test. Law
enforcement, however, is not a scientific field. Therefore, general
acceptance within law enforcement circles cannot be the basis for
finding scientific evidence admissible under Frye.
    The trial court found that the relevant scientific fields to which the
HGN test belongs are optometry and medicine, specifically the
medical specialty of ophthalmology.
    We agree with the trial court that the relevant scientific fields that
embrace the testing for and observation of HGN include medicine,
ophthalmology, and optometry. Research and expert opinion in other
scientific or medical fields, such as neurophysiology, might also be
relevant.
    Thus, the question of general acceptance must be determined from
the testimony of experts and the literature in these scientific fields, and
not from the testimony or writings of law enforcement officers or
agencies.3 Similarly, despite Dr. Henson’s years of experience, his


   3
    Some Illinois cases have phrased the Frye test in terms that would seem
to require the expert witness whose testimony is used to admit the scientific
evidence at trial to be a member of the scientific field to which the scientific
evidence belongs. See, e.g., In re Marriage of Gambla, 367 Ill. App. 3d 441,
460 (2006) (stating that under Frye, “the proponent of expert testimony
predicated upon a scientific theory must establish that the theory has gained
general acceptance in the expert’s scientific field” (emphasis added)).
      This has never been a requirement under Frye, which requires the court
to determine whether the science underlying a witness’s testimony is
generally accepted in the relevant scientific field. Whether the testifying
witness is qualified to give the scientific testimony is a separate question.
      Thus, a police officer trained as an accident-reconstruction expert may
be qualified to testify regarding the use of certain principles of physics to
determine how fast a vehicle was traveling at the moment of impact, even
though the expert is not a physicist. So long as the scientific principles being
applied are generally accepted in the field to which they belong–physics–the

                                     -16-
professional credentials do not qualify him as an expert on the general
acceptance of HGN testing for the purpose of alcohol impairment
within these scientific fields.

                           General Acceptance
     Defendant argues that the presence of HGN is not a reliable
indicator of impairment due to alcohol. She points to testimony that
the presence of HGN correlates with blood-alcohol concentrations of
0.04 to 0.06, which is lower than the statutory definition of
intoxication. The State responds that defendant was not charged with
driving with a blood-alcohol concentration over the legal limit (625
ILCS 5/11–501(a)(2) (West 2006)); she was charged with aggravated
DUI (625 ILCS 5/11–501(d)(1)(C) (West 2006)), and that a driver
may be impaired with a blood-alcohol concentration below 0.08.
     Defendant also argues that an individual may fail the HGN test due
to as many as 125 conditions unrelated to alcohol ingestion. The State
answers that the testimony clearly shows that the eye movements
elicited by the HGN test are readily distinguishable from other forms
of nystagmus and that these differences are obvious to a properly
trained observer.
     These points of disagreement and the issues raised at oral
argument reveal that before we can determine whether a scientific
principle is generally accepted, we must define the purpose for which
it is being used at trial. Our remand for a Frye hearing directed the
trial court to determine whether a failed HGN test was generally
accepted in the relevant scientific community as an indicator of
impairment due to alcohol. McKown I, 226 Ill. 2d at 276.
     The testimony by witnesses for both parties consistently stated
that the presence of the physical sign of HGN is indicative of CNS
depression due to the consumption of alcohol. This sign may also
indicate some other form of CNS depression. There is also general


otherwise qualified expert may testify regarding those principles.
      Similarly, our conclusion that the science of HGN testing belongs to the
fields of medicine and optometry for purpose of the Frye hearing does not
preclude a police officer from testifying regarding the performance of the test
and the results observed.

                                     -17-
agreement among the testifying experts that when the subject has
consumed alcohol, HGN is not necessarily a sign of impairment as a
result of that alcohol consumption.
     The trial court concluded that “both ophthalmology and optometry
generally accept the principle that the HGN test may be an indicator
of alcohol consumption.” The trial court stated, further, that the use
of HGN test results at trial “should be limited to the conclusion that
a ‘failed’ test suggests that the subject may have consumed alcohol
and may [have] be[en] under the influence. There should be no
attempt to correlate the test results with any particular blood-alcohol
level or range or level of intoxication.”
     We agree. Consumption of alcohol is a necessary precondition to
impairment due to alcohol. Therefore, any evidence of alcohol
consumption is relevant to the question of impairment. See People v.
Beaman, 229 Ill. 2d 56, 75-76 (2008) (stating that evidence is relevant
if it tends to make the existence of any fact in consequence more or
less probable than it would be without the evidence); Black’s Law
Dictionary 1404 (9th ed. 2009) (defining relevant as “[l]ogically
connected and tending to prove or disprove a matter in issue”). A
failed HGN test is relevant to impairment in the same manner as the
smell of alcohol on the subject’s breath or the presence of empty or
partially empty liquor containers in his car. Each of these facts is
evidence of alcohol consumption and is properly admitted into
evidence on the question of impairment.
     We, therefore, adopt the trial court’s finding that HGN testing is
generally accepted in the relevant scientific fields and that evidence of
HGN test results is admissible for the purpose of proving that a
defendant may have consumed alcohol and may, as a result, be
impaired.

                    Decisions of Our Sister States
    Our conclusion that HGN testing is generally accepted is
consistent with that of other states that have conducted Frye hearings
on this question. See Ballard v. State, 955 P. 2d 931 (Alaska App.
1998) (HGN test results admissible to show that a defendant has
consumed alcohol and is potentially impaired); State v. Superior
Court, 149 Ariz. 269, 718 P.2d 171 (1986) (holding that with proper

                                  -18-
foundation, testimony regarding nystagmus is admissible as evidence
that a defendant was driving while under the influence of alcohol);;
People v. Joehnk, 35 Cal. App. 4th 1488, 42 Cal. Rptr. 2d 6 (1995)
(when combined with results of other field-sobriety tests and with the
officer’s observations, HGN is a useful tool in reaching opinion as to
whether a defendant is intoxicated); State v. Klawitter, 518 N.W.2d
577 (Minn. 1994) (HGN testing satisfies Frye test); State v. Baue, 258
Neb. 968, 607 N.W.2d 191 (2000) (HGN evidence admissible for
limited purpose of showing the defendant had an impairment that may
have been caused by alcohol, but not admissible for proving blood-
alcohol concentration in excess of legal limit); State v. Baity, 140
Wash. 2d 1, 991 P.2d 1151 (2000) (use of HGN as forensic test to
determine intoxication satisfies Frye).
    Defendant argues that reliance on these cases is misplaced either
because the cases have been undermined by later developments or
because the Frye issue was not as fully litigated, as it has been in the
present case. Because we do not rely on these cases as support for our
holding, but merely acknowledge that our conclusion is consistent
with them, we reject defendant’s argument that our reliance on these
cases is misplaced.

           Limits on Admission of HGN Evidence at Trial
    Defendant argues that the use of HGN evidence should be limited
to use at a preliminary hearing to establish probable cause to arrest.
She argues that the HGN test is not sufficiently reliable to be used as
evidence of guilt because it does not prove impairment beyond a
reasonable doubt. Defendant cites no authority for imposing such a
limitation but urges this court, as “gatekeeper of evidence,” to declare
that HGN test results may not be used at trial.
    Defendant overlooks the threshold requirement of relevance. Each
individual item of evidence does not have to prove the fact at issue
beyond a reasonable doubt. Rather, each individual item of evidence
must tend to show that the fact at issue, in this case impairment due
to alcohol, is more or less likely. By way of analogy, it is often said
that “ ‘a brick is not a wall.’ ” Fed. R. of Evid. 401, Advisory
Committee’s Note, quoting C. McCormick, Handbook of the Law of
Evidence §152, at 317 (1954). That is, an individual item of evidence


                                 -19-
is merely a brick, one of many bricks used to build the wall that is the
fact at issue.
     The police officer’s testimony regarding the results of a
defendant’s failed HGN test tends to show that he or she consumed
alcohol prior to being tested. Similarly, testimony that a defendant did
not display any sign of HGN is relevant evidence that tends to show
that he or she had not consumed alcohol. The result of the test,
therefore, makes it either more or less likely that a defendant was
impaired due to alcohol.
     This is the concern addressed by the trial court’s conclusion that
the use of HGN evidence should be limited to proof of alcohol
consumption and the possibility of resulting impairment. Limitation
may take the form of sustaining an objection to certain questions or
arguments made by the prosecutor, giving a limiting instruction at the
time the testimony is given, or giving a written jury instruction at the
conclusion of the case. The need for a limitation on the use of the
evidence, however, is not a basis for finding the evidence inadmissible
at trial under the test of Frye.
     We, therefore, reject defendant’s invitation to limit the use of this
relevant piece of evidence to showing probable cause.
     Defendant also argues that despite its relevance, a failed HGN test
result “proves too much” because of its “aura” of scientific certainty.
In effect, she is arguing that the risk of undue prejudice from this
evidence substantially outweighs its probative value. See People v.
Walker, 211 Ill. 2d 317, 337 (2004) (“Illinois courts have long
recognized, as a matter of common law, that a trial court may exercise
its discretion to exclude evidence, even when it is relevant, if its
prejudicial effect substantially outweighs its probative value”).
     This balancing of risk of prejudice versus probative value is not
performed across the board. It is necessarily a case-by-case analysis.
Our finding that HGN evidence meets the Frye standard does not
preclude the possibility that, in a given case, the trial court might rule
such evidence inadmissible on grounds of undue prejudice.
     Defendant also asserts that there is insufficient oversight of police
officers who administer the HGN test in the field, particularly with
regard to their qualifications and their ability to interpret the test
results. She argues that field studies and anecdotal evidence suggest

                                  -20-
that the “vast majority” of police officers improperly perform the test
in arrest situations. In light of this, she argues for more extensive
training of police officers and for stricter standards regarding the
procedure for performing the test in the field. Specifically, she claims
that if HGN evidence does meet the Frye standard, the only
acceptable method for administering the HGN test by a police officer
is the NHTSA method.
     This argument merges two separate questions: first, the proper
method for conducting HGN testing in the field and, second, the
qualifications of the witness who will testify regarding the HGN test
results.
     The trial court framed the question before it on remand in terms
of the general acceptance of the “NHTSA roadside HGN test.” The
evidence presented by both parties was geared toward the test as
developed and taught by the NHTSA. Thus, the trial court’s ruling on
the Frye issue necessarily imported the NHTSA standard testing
protocol. Our adoption of the trial court’s conclusion is similarly
limited.
     We hold that evidence of HGN field-sobriety testing, when
performed according to the NHTSA protocol by a properly trained
officer, is admissible under the Frye test for the purpose of showing
whether the subject has likely consumed alcohol and may be impaired.
     As for the qualifications of the individual witness, the trial court
concluded that a proper foundation must be laid, including a showing
that the witness is properly trained and that he performed the test in
accordance with proper procedures.
     We agree. A properly trained police officer who performed the
HGN field test in accordance with proper procedures may give expert
testimony regarding the results of the test. We also agree with the trial
court’s conclusion that a testifying officer may use the HGN test
results as a part of the basis for his opinion that the defendant was
under the influence and impaired.
     In sum, we affirm each of the trial court’s five conclusions of law.

 Whether the HGN Test Was Properly Administered by the Officer
                         in This Case
  Defendant’s final argument is that even if evidence of HGN field

                                  -21-
testing is generally admissible under Frye, the evidence should not
have been admitted against her because the test was not administered
by Officer Klatt in compliance with NHTSA standards. Specifically,
she argues that Klatt did not testify that he checked her eyes for equal
tracking before conducting the HGN test. He did not testify that he
checked her eyes for equal pupil size. He did not describe the speed
at which he moved the stylus or that he held the stylus at the point of
maximum deviation for the requisite four seconds. He did not testify
that he repeated the procedure twice, as NHTSA protocol requires.
Finally, he confused two of the clues when he combined two steps in
the protocol. As a result, defendant argues, Klatt’s testimony
regarding the HGN test should have been excluded and, further, he
should not have been allowed to express an opinion that she was
impaired because his opinion was necessarily based on the result of the
improperly performed test. She argues further that because the trial
court relied “heavily” on this evidence, her conviction should be
reversed. Finally, she argues that a new trial is barred by double
jeopardy.
     The State argues that defendant forfeited any argument on this
issue by failing to raise it at trial and in a posttrial motion. People v.
Enoch, 122 Ill. 2d 176, 186 (1988). The State notes that because the
defendant failed to raise this issue at trial, it was deprived of the
opportunity to cure any defect in the officer’s foundation testimony at
that time. People v. Bush, 214 Ill. 2d 318, 333 (2005).
     In her brief to the appellate court, defendant argued that the State
failed to present an adequate foundation for the results of her HGN
test to be admitted. She did not argue that trial counsel was ineffective
for failing to make a timely objection and to raise the issue in a
posttrial motion. She did not argue that admission of the officer’s
testimony regarding HGN was plain error.
     The State, however, failed to bring defendant’s forfeiture of the
issue to the attention of the appellate court. In effect, the State
forfeited its ability to argue forfeiture by the defendant. People v.
Williams, 193 Ill. 2d 306, 347 (2000) (doctrine of forfeiture applies
to the State as well as to the defendant and State may forfeit claim
that the defendant forfeited an issue by not properly preserving it for
review).
     The appellate court addressed the issue on the merits, finding that

                                  -22-
a sufficient foundation was presented for the admission of the test
result.
    In her petition for leave to appeal, defendant raised only the single
issue of the necessity for a Frye hearing. On this issue, she prevailed
and was granted remand for a Frye hearing.
    At the Frye hearing, defense counsel attempted to question Dr.
Citron as to whether Klatt correctly performed the HGN test
according to NHTSA standards. The State objected. Counsel
explained that his position was that while an HGN test performed
according to these standards might meet the Frye standard for
admissibility, the test as performed by the officer in this case did not
meet the Frye standard. The trial court sustained the objection,
reasoning that if the Frye hearing had been held at trial, the question
of admissibility of HGN testing in general would have been resolved
prior to the receipt of the officer’s testimony. Thus, the question on
remand was to be answered as a general matter. Any question
regarding the admissibility of a specific test in an individual case was
one to be answered at trial. Defense counsel was allowed to make an
offer of proof. Citron testified that he had reviewed the transcript of
Officer Klatt’s testimony and that the examination as described by
Klatt did not follow the NHTSA standardized protocol for HGN
testing. As a result, he opined, the test was invalid.
    Similarly, defense counsel was allowed to make an offer of proof
during cross-examination of Master Sergeant Lebron. Lebron
reviewed the transcript of Officer Klatt’s trial testimony and stated
that Klatt performed the test while defendant was seated; while the
NHTSA manual requires that the subject be standing. Further, Klatt’s
testimony does not indicate that he questioned defendant about any
eye problems, equal tracking, equal pupil size, or resting nystagmus.
Lebron stated that he “would agree” with the statement that Klatt did
not perform the test in accordance with NHTSA standards.
    During its cross-examination of Dr. Citek, the defense again made
an offer of proof regarding the manner in which Klatt conducted the
HGN test in this case. Citek acknowledged that the officer’s testimony
did not state that he observed equal pupil size and equal tracking
before he conducted the HGN test and that if the officer did skip these
steps, the test results would not be reliable.


                                  -23-
     Page acknowledged that the HGN test must be performed
according to NHTSA standards to be considered reliable as a field-
sobriety test and that he has seen trained police officers administer the
test incorrectly. He agreed that Klatt’s trial testimony did not correctly
describe the clues one observes when administering the HGN test.
     Dr. Henson reviewed Klatt’s testimony and stated based on that
testimony, the test Klatt performed was not in compliance with
NHTSA standards.
     Notwithstanding the testimony on remand in which even the
State’s witnesses found Klatt’s testimony insufficient to lay the
foundation for HGN evidence, the State argues that because defendant
failed to raise the issue in her petition for leave to appeal, she again
forfeited any claim that the foundation for the officer’s testimony
regarding her HGN test results was insufficient. People v. Carter, 208
Ill. 2d 309, 318 (2003) (failure to include an issue in a petition for
leave to appeal results in forfeiture of that issue for review).
     The State is correct that an issue may be deemed forfeited if a
petitioner fails to raise it in his petition for leave to appeal. However,
as we explained in In re Rolandis G., 232 Ill. 2d 13, 37 (2008), “the
failure to raise an issue in a petition for leave to appeal is not a
jurisdictional bar to this court’s ability to review a matter.”
     Whether to review a forfeited issue under these circumstances is
within this court’s discretion. Rolandis G., 232 Ill. 2d at 37. We have
established a clear framework for the exercise of such discretion.
When an issue is not specifically mentioned in a party’s petition for
leave to appeal, but it is “ ‘inextricably intertwined’ ” with other
matters properly before the court, review is appropriate. Rolandis G.,
232 Ill. 2d at 37, quoting Hansen v. Baxter Healthcare Corp., 198 Ill.
2d 420, 430 (2002). If, however, the forfeited issue is not inextricably
intertwined with the issues properly before the court, the forfeiture
rule should be given effect.
     The issues properly before this court in the present appeal are
whether, in general, evidence regarding HGN testing of a defendant
in a DUI prosecution is admissible under the Frye test and, if so, what
circumstances must be present before such evidence may be admitted
in a specific case. We conclude that the forfeited question is
inextricably intertwined with the issues that we have addressed herein,


                                  -24-
particularly given the clear record Klatt’s testimony did not meet the
standards we have now adopted.
    Admission of Klatt’s testimony regarding the HGN test he
performed in the absence of a proper foundation was error. Error will
be deemed harmless and a new trial unnecessary when “the competent
evidence in the record establishes the defendant’s guilt beyond a
reasonable doubt and it can be concluded that retrial without the
erroneous admission of the challenged evidence would produce no
different result.” People v. Arman, 131 Ill. 2d 115, 124 (1989).
    In McKown I, we rejected the State’s argument that if denial of a
Frye hearing was error, it was harmless error. “Given the fact[s] that
defendant’s blood-alcohol content was not verified by any chemical
test, and no other field-sobriety tests were given,” we found it
“reasonable to conclude that the trial court relied heavily on the
improperly admitted HGN test results.” McKown I, 226 Ill. 2d at 276.
In light of our earlier decision, defendant’s conviction must be
reversed.
    We must now consider whether a new trial would subject
defendant to double jeopardy. See People v. Jones, 175 Ill. 2d 126,
134 (1997); People v. McDonald, 125 Ill. 2d 182, 201 (1988). If the
evidence presented at the first trial, including the improperly admitted
evidence, would have been sufficient for any rational trier of fact to
find the essential elements of the crime proven beyond a reasonable
doubt, retrial is the proper remedy. People v. Lopez, 229 Ill. 2d 322,
367 (2008). If no rational trier of fact could so find, defendant may
not be subjected to a second trial.
    In her brief, defendant argues that because the results of her HGN
test should not have been admitted into evidence, Klatt’s opinion,
which was based in part on the test results, should also be excluded
and that remand for a new trial would, therefore, violate double
jeopardy. She offers no authority for the proposition that an opinion
witness who is barred from testifying regarding one fact that entered
into the formation of his opinion is barred from giving an opinion
altogether. Further, she offers no authority for the proposition that a
police officer cannot testify to the facts and circumstances he observed
while investigating an accident.
    We agree with the State that a new trial is proper. There is no bar


                                 -25-
to the officer’s testifying regarding the facts and circumstances he
observed while investigating the accident. In addition, the officer’s
opinion regarding defendant’s state of intoxication was supported by
other facts in the record, aside from her performance on the HGN test.
    Klatt testified that defendant had already been transported from
the scene when he arrived. He found a partially full can of beer in her
car. He spoke to defendant later at the hospital and observed that her
speech was slurred, her eyes were bloodshot, and she had a strong
odor of beer on her breath. Although she initially denied drinking that
day, she later admitted to him that she had consumed two cans of beer
before leaving her house, another can while driving, and had opened
a fourth can just prior to the accident. She also stated that she had
slept only four hours the previous night. At that point, Klatt
performed the HGN test. Because defendant was seated in a hospital
bed, he was unable to perform other field-sobriety tests.
    There was sufficient information in Klatt’s possession prior to his
conducting the HGN test to allow him to form an opinion regarding
defendant’s impairment due to alcohol. At the time he interviewed
defendant, he already suspected her of driving under the influence
based on the statements of the other witnesses and the open can of
beer he found in her car. Her speech, eyes, and breath confirmed his
suspicion. Her admission that she had consumed three cans of beer
and was in the process of consuming a fourth can, after having only
four hours of sleep, provided further confirmation. The result of the
HGN test he performed may have merely provided additional support
for his opinion. We conclude that Klatt may testify regarding these
other facts and to the opinion he formed based on these facts. 4
    In addition, three witnesses other than the officer testified
regarding the accident. Randall Retherford, another motorist, testified
that he drove his truck onto the shoulder of the road to avoid the
defendant’s car, which was approaching him at high speed. He saw


 4
  We note also that while the admission of the HGN test results in this case
was error, it was error because the State did not lay the proper foundation,
not because HGN test results are inadmissible in general. Thus, if the State
can lay the proper foundation for Klatt’s testimony on remand, the test
results will be admissible.

                                   -26-
the defendant’s vehicle “lock up its wheels, veer to the left,” and hit
three on-coming motorcycles.
    His testimony was corroborated by one of the injured riders,
Robert Stanley, who testified that as he lay on the ground after being
thrown from his motorcycle, defendant approached him and offered
to help him remove his helmet. He testified that he smelled the odor
of beer on her breath.
    Another cyclist who was not involved in the accident, Chad
Morris, testified that he heard squealing tires and saw defendant’s car
veering into his lane, sliding sideways into the oncoming motorcycles.
He was able to stop in time to avoid being hit.
    Viewing the testimony of these witnesses, in combination with the
admissible portion of Officer Klatt’s testimony, in the light most
favorable to the prosecution (see People v. Diggins, 235 Ill. 2d 48, 58
(1999)), there was sufficient evidence from which the trial court could
have found defendant guilty of aggravated driving under the influence
of alcohol beyond a reasonable doubt and, thus, double jeopardy does
not preclude a new trial. See People v. Hope, 116 Ill. 2d 265, 279
(1986). However, we note that nothing in this opinion should be
construed as a finding regarding defendant’s guilt that would be
binding upon remand.
    Defendant argued in McKown I that the odor of alcohol on her
breath merely indicated that she had consumed alcohol, not that she
was impaired. She also argued that her bloodshot eyes could be
explained by her recent overnight shift working in a chemical plant.
These are arguments better addressed to the trier of fact. She is free
to make these arguments at her new trial.

                            CONCLUSION
     In sum, we adopt the trial court’s findings on remand that HGN
testing is generally accepted in the relevant scientific fields as evidence
of alcohol consumption and possible impairment. We also adopt the
trial court’s five conclusions of law regarding the admission of HGN
evidence and its use at trial. The admissibility of HGN evidence in an
individual case will depend on the State’s ability to lay a proper
foundation and to demonstrate the qualifications of its witness, subject
to the balancing of probative value with the risk of unfair prejudice.

                                   -27-
    We find that admission of the officer’s testimony regarding HGN
testing in this case was reversible error. Thus, we reverse the
judgments of the appellate and circuit courts and remand the cause to
the circuit court for a new trial.

                                               Judgments reversed;
                                                  cause remanded.




                                -28-
