                    FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

MATTHEW HEAD,                             
               Plaintiff-Appellant,
                                                No. 03-35567
                v.
GLACIER NORTHWEST,                               D.C. No.
                                               CV-02-00373-MA
INCORPORATED, a Washington
                                                    OPINION
corporation,
              Defendant-Appellee.
                                          
         Appeal from the United States District Court
                  for the District of Oregon
         Malcolm F. Marsh, District Judge, Presiding

                   Argued and Submitted
             December 8, 2004—Portland, Oregon

                        Filed July 6, 2005

    Before: Thomas G. Nelson and Johnnie B. Rawlinson,
        Circuit Judges; and William W Schwarzer,*
                   Senior District Judge.

         Opinion by Senior District Judge Schwarzer;
             Concurrence by Judge T.G. Nelson




  *The Honorable William W Schwarzer, Senior United States District
Judge for the Northern District of California, sitting by designation.

                                7865
               HEAD v. GLACIER NORTHWEST, INC.            7869


                         COUNSEL

Scott N. Hunt, Busse & Hunt, Portland, Oregon, for the
plaintiff-appellant.

William T. Grimm, Davis Grimm Payne & Marra, Seattle,
Washington, for the defendant-appellee.


                         OPINION

SCHWARZER, Senior District Judge:

   Matthew Head appeals the district court’s grant of partial
summary judgment in his action against his former employer,
Glacier Northwest (“Glacier”), on his claims for disability
discrimination under the Americans with Disabilities Act
(“ADA”) and Oregon state law on the basis of disability and
record of disability. Head also appeals the district court’s
exclusion of lay opinion testimony during the trial on his per-
ceived disability and retaliation claims. Finally, Head chal-
lenges the district court’s jury instructions requiring him to
demonstrate that Glacier discriminated against him “because
7870           HEAD v. GLACIER NORTHWEST, INC.
of” his perceived disability and retaliated against him “be-
cause” of his request for an accommodation. We have juris-
diction pursuant to 28 U.S.C. § 1291. We reverse the grant of
summary judgment, affirm the exclusion of lay opinion testi-
mony, vacate the jury verdict, and remand for further pro-
ceedings consistent with this opinion.

I.   FACTS AND PROCEDURAL HISTORY

   On June 29, 2001, Glacier, Matthew Head’s employer, ter-
minated him after he got a loader he was operating stuck in
the mud. The loader had to be extracted by another piece of
equipment. In terminating Head, Glacier cited damage to the
loader in violation of an equipment abuse policy issued in
2000. It was undisputed that Head had received this policy.

   In early 2001, prior to his termination, Head was diagnosed
with depression or bipolar disorder. Head informed Glacier of
this diagnosis. At the time of his diagnosis, Head worked
graveyard shift as a barge offloader. Head subsequently
missed almost two months of work because of his disability.
Head requested, and was granted, a Family Medical Leave of
Absence for this time period. Although Head returned to work
in May 2001, his doctors restricted him from working more
than 12 hours per day or 48 hours per week. The doctors also
limited Head to working only the day shift.

   After his termination, Head filed numerous claims in fed-
eral district court. Of relevance to this appeal were Head’s
claims under the ADA and Oregon law for disability discrimi-
nation based on Head’s disability, record of disability, or per-
ceived disability, and for retaliation for requesting an
accommodation. Glacier moved for summary judgment. In
opposition to Glacier’s motion, Head did not submit medical
or comparative evidence in support of his claims, but did sub-
mit numerous affidavits and other evidence. Ultimately, the
district court granted partial summary judgment in favor of
Glacier on Head’s discrimination claims based on disability
                 HEAD v. GLACIER NORTHWEST, INC.              7871
and a record of disability. The court reasoned that Head had
failed to demonstrate a genuine issue of material fact regard-
ing substantial impairment because he did not present any
medical or comparative evidence to support his claims that his
disability substantially impaired any major life activities.

   The remainder of Head’s claims, for (1) discrimination
under the ADA and Oregon law for perceived disability, and
(2) retaliation under the ADA and Oregon law for requesting
an accommodation, went to trial. The rest of the issues on
appeal relate to facts that occurred during the trial.

   During the trial, Head’s counsel asked a lay witness the fol-
lowing question about the incident with the loader that pre-
ceded Head’s termination: “Was there anything about the
position where Mr. Head was stuck or the location of the
loader in the material it was stuck in that caused you to
believe that he had violated the equipment abuse policy?”
Glacier’s counsel objected. The district court sustained the
objection based on its earlier decision that lay opinion testi-
mony regarding whether Head’s getting the loader stuck con-
stituted equipment abuse would not be allowed. The district
court believed that such testimony should not be allowed
under Federal Rule of Evidence 701. Accordingly, the witness
did not answer counsel’s question.

   As the trial neared its conclusion, the court and parties dis-
cussed the jury instructions. Of primary concern was whether
to give a single-motive “because of” instruction or a mixed-
motive “motivating factor” instruction for Head’s state and
ADA-based discrimination and retaliation claims. Relying on
Costa v. Desert Palace, Inc.,1 a Title VII case, the district
court concluded that single-motive “because of” instructions
were appropriate.2 The jury instruction for disability discrimi-
  1
   299 F.3d 838 (9th Cir. 2002), aff’d, 539 U.S. 90 (2003).
  2
   Id. Costa states that:
7872             HEAD v. GLACIER NORTHWEST, INC.
nation therefore required Head to prove that Glacier termi-
nated him “because of” his perceived disability. The jury
instruction for retaliation due to a request for accommodation
therefore required Head to prove that Glacier discharged him
solely “because” he requested a reasonable accommodation.
The jury returned a verdict in favor of Glacier.

   Head now appeals the district court’s partial grant of sum-
mary judgment, the district court’s exclusion of lay witness
testimony regarding whether he violated the equipment abuse
policy, and the jury instructions. Head argues that the district
court erred by requiring medical and comparative evidence to
substantiate the substantial impairment of major life activities
at the summary judgment stage. We agree and reverse and
remand as to this issue. Head argues that the district court
improperly excluded the lay witness testimony. We disagree
and affirm as to this issue. Finally, Head argues that the dis-
trict court erred by giving “because of” and “because” jury
instructions rather than “motivating factor” instructions. We
agree, vacate the jury verdict, and remand as to this issue.

    If, based on the evidence, the trial court determines that the only
    reasonable conclusion a jury could reach is that discriminatory
    animus is the sole cause for the challenged employment action or
    that discrimination played no role at all in the employer’s deci-
    sionmaking, then the jury should be instructed to determine
    whether the challenged action was taken “because of” the prohib-
    ited reason.
    ...
    In contrast, in cases in which the evidence could support a find-
    ing that discrimination is one of two or more reasons for the chal-
    lenged decision, at least one of which may be legitimate, the jury
    should be instructed to determine . . . whether the discriminatory
    reason was “a motivating factor” in the challenged action.
Costa, 299 F.3d at 856-57 (emphasis in original). The district court was
correct in assuming that Costa applies to ADA actions. See infra Part
III.B.2.
                 HEAD v. GLACIER NORTHWEST, INC.                   7873
II.   SUMMARY JUDGMENT

   We review the district court’s grant of summary judgment
de novo.3 We only review “ ‘evidence available to the [dis-
trict] court at the time the motion was made.’ ”4 The facts
must be viewed in the light most favorable to Head.5

   We hold that Ninth Circuit precedent does not require com-
parative or medical evidence to establish a genuine issue of
material fact regarding the impairment of a major life activity
at the summary judgment stage. Rather, our precedent sup-
ports the principle that a plaintiff’s testimony may suffice to
establish a genuine issue of material fact. McAlindin v.
County of San Diego6 and Fraser v. Goodale are illustrative.

   In McAlindin, we discussed medical evidence, but did not
explicitly or otherwise require it.7 In fact, we held that a state-
ment in a declaration by McAlindin alone sufficed to raise a
genuine issue of material fact regarding the impairment of a
major life activity: his ability to engage in sexual relations.8
Additionally, McAlindin’s declaration played a central role in
our holding that sufficient evidence supported the existence of
a genuine issue of material fact as to his sleeping claim.9
Finally, although we discussed doctors’ evaluations of
McAlindin’s inability to interact with others, we held that
“[h]is alleged ‘fear reaction’ and ‘communicative paralysis’
are sufficiently severe to raise a genuine issue of material fact
  3
    Fraser v. Goodale, 342 F.3d 1032, 1037 (9th Cir. 2003), cert. denied,
541 U.S. 937 (2004).
  4
    Id. at 1036 (quoting Hopkins v. Dow Corning Corp., 33 F.3d 1116,
1121 (9th Cir. 1994)) (parallel citation omitted).
  5
    Id. at 1037.
  6
    192 F.3d 1226 (9th Cir. 1999).
  7
    See McAlindin, 192 F.3d at 1235-36.
  8
    Id. at 1235.
  9
    See id.
7874             HEAD v. GLACIER NORTHWEST, INC.
about his ability to interact with others.”10 Granted, this hold-
ing regarding the inability to interact with others relied more
on medical testimony than did our conclusions regarding the
other two major life activities, but we did not require medical
testimony.

   Fraser also did not require medical or comparative evi-
dence at the summary judgment stage. In Fraser, a diabetic
argued that her diabetes substantially limited the major life
activities of eating, caring for herself, and thinking and commu-
nicating.11 After determining that under certain circumstances
eating is a major life activity, we held that Fraser’s presenta-
tion of evidence about her demanding and highly difficult
treatment regimen precluded a grant of summary judgment.12
The evidence on which we relied consisted primarily of Fra-
ser’s testimony regarding her dietary regime. We also consid-
ered some medical testimony that even if Fraser perfectly
followed her regime she could still have complications; how-
ever, we placed no emphasis on this medical testimony.13
Thus, Fraser indicates that medical testimony may be helpful,
but it is not required.

   [1] Additionally, in rejecting Fraser’s claim that she was
substantially limited in caring for herself and thinking and
communicating, we faulted the quantity of the evidence pres-
ented, not the nature of it.14 We concluded that although Fra-
ser’s statements showed the effects on these life activities,
there was insufficient “evidence that she is so unsuccessful in
monitoring her blood sugar levels that she is substantially
limited in [these major life activities].”15 Accordingly, Fraser
  10
     Id. at 1235-36.
  11
     Fraser, 342 F.3d at 1041.
  12
     See id. at 1042.
  13
     Id. at 1041-42.
  14
     Id. at 1043-44.
  15
     Id. at 1043 (emphasis added).
                 HEAD v. GLACIER NORTHWEST, INC.                    7875
supports the principle that a plaintiff’s testimony may suffice
to establish a genuine issue of material fact. Consequently, it
follows that comparative or medical evidence at the summary
judgment stage is not required. We hasten to add that our
holding in no way impugns our longstanding precedent that
conclusory declarations are insufficient to raise a question of
material fact.16 To survive summary judgment, an affidavit
supporting the existence of a disability must not be merely
self-serving and must contain sufficient detail to convey the
existence of an impairment.17

   Because we conclude that plaintiffs need not supply com-
parative or medical evidence if they provide other adequate
evidence, we must now determine whether Head provided
adequate evidence in this case. Thus, to determine whether
the grant of summary judgment was appropriate, we review
Head’s alleged impairment of each major life activity.18 We
conclude that Head has alleged sufficient evidence to demon-
strate a substantial impairment in the established major life
activities of sleeping, interacting with others, and thinking.
Moreover, we conclude that reading is a major life activity,
and that Head has alleged sufficient evidence of a substantial
impairment regarding reading.19 Accordingly, we reverse the
grant of summary judgment as to each claimed major life
activity.
  16
    See FTC v. Publ’g Clearing House, Inc., 104 F.3d 1168, 1171 (9th
Cir. 1997).
  17
    Id.
  18
    Fraser, 342 F.3d at 1040-44.
  19
    Head also argues that he is substantially impaired in the major life
activities of caring for himself and concentrating. However, we decline to
consider these additional major life activities because Head did not raise
them before the district court. See Pfingston v. Ronan Eng’g Co., 284 F.3d
999, 1003-04 (9th Cir. 2002).
7876             HEAD v. GLACIER NORTHWEST, INC.
  A.     Sleeping

   [2] Sleeping is a major life activity.20 Head’s declaration
alleging great difficulty sleeping at night, with some improve-
ment when using sleep medication, suffices to raise a genuine
issue of material fact.21 He explained that:

       [even] after getting on medication my sleeping
       improved but I still periodically had serious prob-
       lems. I would pass out for a while immediately after
       getting home from work. But I would not get a full
       night’s sleep, and then after I woke up I had great
       difficulty going to sleep when it was time to go to
       bed for the night. This went on for months. Even
       with the medication I usually was only able to sleep
       five or six hours a night, compared to the seven to
       nine hours a night I slept prior to my diagnosis. I was
       drowsy during the day due to the medications and
       lack of sleep. Some nights even with the help of
       medications I could not get to sleep for hours or even
       at all.



Under McAlindin, this is sufficient evidence to preclude sum-
mary judgment.22 Accordingly, Head has alleged sufficient
evidence to demonstrate a substantial impairment in the major
life activity of sleeping.

  B.     Interacting with Others

   Interacting with others is a major life activity.23 To demon-
strate a substantial impairment in the ability to interact with
  20
     McAlindin, 192 F.3d at 1230.
  21
     See id. at 1235.
  22
     See McAlindin, 192 F.3d at 1235.
  23
     Id. at 1230.
                HEAD v. GLACIER NORTHWEST, INC.                7877
others, Head “must show that his ‘relations with others were
characterized on a regular basis by severe problems, for
example, consistently high levels of hostility, social with-
drawal, or failure to communicate when necessary.’ ”24 At the
summary judgment stage, an “alleged ‘fear reaction’ and
‘communicative paralysis’ are sufficient[ ] to raise a genuine
issue of material fact about [Head’s] ability to interact with oth-
ers.”25

   In McAlindin, the testimony of doctors established that
McAlindin was always anxious. This led McAlindin “to con-
strict outside activities and stay away from crowds, shopping
centers and any disagreement with his wife.”26 He was around
the house at least 20 hours a day and confined his social activ-
ities to his family.27 We emphasized that this occurred “all of
the time.”28

   [3] In this case, Head’s affidavit alleges that he avoids
crowds, stores, large family gatherings, and even doctor’s
appointments. Furthermore, Head would not leave the house
most weekends before he was fired, and after he was fired he
would not leave the house for weeks on end. Head even
avoided telephone interaction unless “there were serious con-
sequences” for not responding to phone calls. Head has not
alleged that this behavior occurs all the time, but rather that
it occurs “many times” or “most” of the time. Thus, Head has
stated facts slightly less severe than those found sufficient in
McAlindin.29 Nonetheless, he has still alleged sufficient facts
to show a “substantial limitation” and to avoid summary judg-
  24
     Id. at 1235 (quoting Equal Employment Opportunity Commission,
EEOC Enforcement Guidance on the Americans with Disabilities Act and
Psychiatric Disabilities 5 (March 25, 1997)).
  25
     Id. at 1235-36.
  26
     Id. at 1235.
  27
     Id.
  28
     Id.
  29
     Id. at 1235-36.
7878              HEAD v. GLACIER NORTHWEST, INC.
ment.30 Accordingly, Head has alleged sufficient evidence to
demonstrate a substantial impairment in the major life activity
of interacting with others.

  C.     Thinking

   [4] Thinking is a major life activity.31 Fraser instructs that
the inability to think three times in five months does not con-
stitute a substantial limitation of the ability to think.32 How-
ever, Head has alleged a much more persistent problem with
his ability to think than that found insufficient in Fraser.33
Head’s affidavit states the following regarding the ability to
think:

          My bipolar disorder and/or depression greatly
       affected my short-term memory and ability to con-
       centrate both before and after I was hospitalized. I
       could not stay focused on something for more than
       brief periods. I did not have much of a short-term
       memory at all. I had to be repeatedly reminded of
       appointments, or tasks I had to do. . . . If I looked at
       written material for too long things just got jumbled
       in my mind and I would have to stop. I could not sit
       and focus on an entire television show. In the fall of
       2001 I quit school because of my inability to focus
       or concentrate adequately.

Taken in the light most favorable to Head, these statements
indicate that his ability to think was almost constantly
impaired at some level. Accordingly, Head has alleged suffi-
  30
     See Fraser, 342 F.3d at 1043.
  31
     Taylor v. Phoenixville Sch. Dist., 184 F.3d 296, 307 (3d Cir. 1999);
see Fraser, 342 F.3d at 1044 (recognizing that “thinking and communicat-
ing” is a major life activity).
  32
     Fraser, 342 F.3d at 1044.
  33
     See id.
                  HEAD v. GLACIER NORTHWEST, INC.                      7879
cient evidence to demonstrate a substantial impairment in the
major life activity of thinking.

  D.    Reading34

   [5] At least one court of appeals has held that reading is a
major life activity.35 We have not previously addressed
whether reading is a major life activity. We now recognize
that reading is a major life activity.

   [6] “Federal regulations describe major life activities as
including functions ‘such as caring for oneself, walking, see-
ing, hearing, speaking, breathing, learning, and working.’ ”36
We have recognized that the “illustrative list of major life
activities requires the activity only to be of ‘comparative
importance’ and ‘central to the life process itself,’ and it need
not have a public, economic, or daily character.”37 To be a
major life activity, the activity need not be essential to sur-
vival, but rather “of central importance to most people’s daily
lives.”38

    [7] The ability to read is necessary in many instances to
perform major life activities such as caring for oneself, learn-
ing, and working. As such, it is of central importance to most
people’s daily lives. To be sure, a person will not die merely
because he or she cannot read, but that is not the standard.
The fact that reading is of comparative importance, and that
it is central to most people’s daily lives, establishes that read-
  34
      Although this claim is arguably a subset of Head’s thinking claim,
because he alleged it separately in the district court, we discuss it sepa-
rately.
   35
      Bartlett v. N.Y. State Bd. of Law Examiners, 226 F.3d 69, 80 (2d Cir.
2000).
   36
      Fraser, 342 F.3d at 1039 (quoting 45 C.F.R. § 84.3(j)(2)(ii); citing 29
C.F.R. § 1630.2(i)) (emphasis omitted).
   37
      Id. at 1039-40 (quoting Bragdon v. Abbott, 524 U.S. 624, 638 (1998)).
   38
      See id. at 1040.
7880             HEAD v. GLACIER NORTHWEST, INC.
ing is a major life activity.39 Consequently, we hold that read-
ing is a major life activity. Accordingly, to survive summary
judgment on his reading claim, Head had to allege sufficient
facts to establish a substantial impairment of his ability to read.40

   [8] In his affidavit, Head alleged that “[r]eading was espe-
cially difficult. I basically did not read for more than three to
five minutes at a time. If I looked at written material for too
long things just got jumbled in my mind and I would have to
stop.” Taking these allegations in the light most favorable to
Head, it appears that his ability to read was substantially
impaired by an inability to read more than a few minutes at
a time. Accordingly, Head has alleged sufficient evidence to
demonstrate a substantial impairment in the major life activity
of reading.

   [9] We hold that Ninth Circuit precedent does not require
comparative or medical evidence to establish a genuine issue
of material fact regarding the impairment of a major life activ-
ity at the summary judgment stage. Under the facts of this
case, Head has made the minimal showing necessary to sur-
vive summary judgment on his claims for substantial impair-
ment of the major life activities of sleeping, interacting with
others, thinking, and reading. Accordingly, we reverse the dis-
trict court and remand for a determination on the merits of
Head’s claims based on disability and record of disability.

III.   TRIAL ERROR

  A.   Lay Opinion Testimony

   We review evidentiary rulings for abuse of discretion.41 We
cannot reverse the district court’s exclusion of lay witness tes-
timony regarding equipment abuse unless we have a definite
  39
     See id. at 1039-40.
  40
     See id. at 1043-44.
  41
     See Tritchler v. County of Lake, 358 F.3d 1150, 1155 (9th Cir. 2004).
                 HEAD v. GLACIER NORTHWEST, INC.                7881
and firm conviction that the district court committed a clear
error of judgment42 and the error was prejudicial.43

   [10] A lay witness may give opinions that are: “(a) ratio-
nally based on the perception of the witness, [and] (b) helpful
to a clear understanding of the witness’[s] testimony or the
determination of a fact in issue. . . .”44 In this case, Head
argues that the district court abused its discretion by not
allowing one of his witnesses to answer the following ques-
tion: “Was there anything about the position where Mr. Head
was stuck or the location of the loader in the material it was
stuck in that caused you to believe that he had violated the
equipment abuse policy?”

   [11] Assuming arguendo that the witness had personal
knowledge about whether getting the loader stuck was likely
to have resulted from equipment abuse, it is unclear how the
witness’s opinion about that would have been helpful to the
jury in this case. The jury was fully capable of comparing the
incident involving the loader with the standards in the equip-
ment abuse policy and drawing its own conclusion. Accord-
ingly, we conclude that the district judge properly sustained
the objection to the question because an answer would not
have been helpful to “the determination of a fact in issue.”45

  B.   Jury Instructions

   Head alleges that the district court erred in giving a “be-
cause of” or “because” instruction as to four of his claims: (1)
the state discrimination claim; (2) the ADA discrimination
claim; (3) the state retaliation claim; and (4) the ADA retalia-
tion claim. To decide these claims, we must determine the
causal standard for each claim and whether the jury instruc-
  42
     See SEC v. Coldicutt, 258 F.3d 939, 941 (9th Cir. 2001).
  43
     See Tritchler, 358 F.3d at 1155.
  44
     FED. R. EVID. 701.
  45
     Id.
7882              HEAD v. GLACIER NORTHWEST, INC.
tions appropriately reflected that standard. At its core, the
causation standard is a legal question; thus, we review it de
novo.46 We review the district court’s formulation of jury
instructions for abuse of discretion,47 but error in jury instruc-
tions does not require reversal if the error was “more probably
than not harmless.”48

   As to the state retaliation claim, the causal standard for
retaliation claims under Oregon Revised Statute § 659A.109
is whether “the unlawful motive was a substantial and imper-
missible factor in the discharge decision.”49 As to the remain-
ing jury instruction claims, we must determine what standard
for causation the ADA requires and how to explain that stan-
dard to a jury.50 We hold that the ADA causation standard is
a motivating factor standard.51 Furthermore, we hold that the
use of the “because of” instruction was prejudicial in this
case. The analysis below first explains how we determined
  46
      Costa, 299 F.3d at 858.
  47
      Tritchler, 358 F.3d at 1154.
   48
      Mockler v. Multnomah County, 140 F.3d 808, 812 (9th Cir. 1998) (cit-
ing Coursen v. A.H. Robins Co., 764 F.2d 1329, 1337 (9th Cir. 1985)).
   49
      McPhail v. Milwaukie Lumber Co., 999 P.2d 1144, 1149 (Or. Ct. App.
2000). Unlike the Oregon state disability claim, retaliation claims under
Oregon Revised Statute § 659A.109 are not within the sections to be con-
strued in accordance with the ADA. See OR. REV. STAT. § 659A.139 (stat-
ing “ORS 659A.112 to 659A.139” are construed in accordance with the
ADA).
   50
      The causal standard under Oregon Revised Statute § 659A.112
(Employment discrimination against disabled persons), “shall be construed
to the extent possible in a manner that is consistent with any similar provi-
sions of the [ADA].” OR. REV. STAT. § 659A.139. Consequently, our deci-
sion regarding causation under the ADA resolves the determination of
causation for a discrimination claim under Oregon law.
   51
      We hold that the ADA “motivating factor” standard for retaliation
claims is a similar standard to Oregon’s “substantial and impermissible
factor” causation standard. See McPhail, 999 P.2d at 1149. Accordingly,
the discussion below regarding the required jury instruction and prejudice
in sections III.B.2 and 3 applies to the Oregon state law retaliation claim
as well as the ADA-based claims.
                   HEAD v. GLACIER NORTHWEST, INC.                       7883
this causation standard, then explains why the jury instruction
in this case should have used the “motivating factor” lan-
guage, and then why the instruction given was prejudicial.

       1.   ADA’s standard of causation

   [12] Causation analysis under the ADA is really a question
of whether the ADA’s use of the causal language “because of,”52
“by reason of,”53 and “because”54 means that discriminatory
and retaliatory conduct is proscribed only if it was solely
because of, solely by reason of, or solely because an employee
was disabled or requested an accommodation. Although the
Ninth Circuit has not answered this question, seven of our sis-
ter circuits have held that the ADA causation standard does
not require a showing of sole cause.55 The Eleventh Circuit in
  52
      42 U.S.C. § 12112(a). Title I applies to the private sector and states
that: “No covered entity shall discriminate against a qualified individual
with a disability because of the disability of such individual in regard to
job application procedures, the hiring, advancement, or discharge of
employees, employee compensation, job training, and other terms, condi-
tions, and privileges of employment.” Id. (emphasis added).
   53
      42 U.S.C. § 12132. Title II applies to the public sector and states that:
“Subject to the provisions of this subchapter, no qualified individual with
a disability shall, by reason of such disability, be excluded from participa-
tion in or be denied the benefits of the services, programs, or activities of
a public entity, or be subjected to discrimination by any such entity.” Id.
(emphasis added).
   54
      42 U.S.C. § 12203(a). Title IV of the ADA precludes retaliation
against employees who seek to enforce their statutory rights under the
ADA. McNely v. Ocala Star-Banner Corp., 99 F.3d 1068, 1073 (11th Cir.
1996). Title IV states that: “No person shall discriminate against any indi-
vidual because such individual has opposed any act or practice made
unlawful by this chapter or because such individual made a charge, testi-
fied, assisted, or participated in any manner in an investigation, proceed-
ing, or hearing under this chapter.” 42 U.S.C. § 12203(a) (emphasis
added).
   55
      Parker v. Columbia Pictures Indus., 204 F.3d 326, 337 (2d Cir. 2000);
Baird ex rel. Baird v. Rose, 192 F.3d 462, 470 (4th Cir. 1999); Foster v.
Arthur Andersen, LLP, 168 F.3d 1029, 1033-34 (7th Cir. 1999); McNely,
7884             HEAD v. GLACIER NORTHWEST, INC.
McNely v. Ocala Star-Banner Corp., an ADA case, thor-
oughly analyzed this question.

   The McNely court analyzed the statutory language,56 legis-
lative history,57 and Supreme Court precedent interpreting
“because of” in Title VII cases.58 It explained that “the
‘because of’ component of the ADA liability standard
imposes no more restrictive standard than the ordinary, every-
day meaning of the words would be understood to imply. In
everyday usage, ‘because of’ conveys the idea of a factor that
made a difference in the outcome.”59

   [13] The McNely court noted that the ADA liability provi-
sions do not contain the word “solely” or any similar terms.
It explained that, given the absence of that term from the stat-
ute, “unless we can discern a very good reason to read the
restrictive term ‘solely’ into two statutory provisions where it
is not found, this is a simple case.”60 The court declined to
import the “solely” restriction from the Rehabilitation Act,
explaining that “[a] liability standard that tolerates decisions
that would not have been made in the absence of discrimina-
tion, but were nonetheless influenced by at least one other
factor, does little to ‘eliminate’ discrimination; instead, it
indulges it.”61 Thus, the court concluded that importing the

99 F.3d at 1076; Katz v. City Metal Co., 87 F.3d 26, 33 (1st Cir. 1996);
Buchanan v. City of San Antonio, 85 F.3d 196, 200 (5th Cir. 1996); Pedigo
v. P.A.M. Transp., Inc., 60 F.3d 1300, 1301 (8th Cir. 1995). But see Hed-
rick v. W. Reserve Care Syst., 355 F.3d 444, 454 (6th Cir. 2004) (holding
that ADA plaintiff must show that disability was sole reason for adverse
employment action).
   56
      McNely, 99 F.3d at 1073-74.
   57
      Id. at 1074-75.
   58
      Id. at 1075-76.
   59
      Id. at 1077.
   60
      Id. at 1073.
   61
      Id. at 1074.
                  HEAD v. GLACIER NORTHWEST, INC.                      7885
term “solely” would undermine the very purpose of the ADA:
“ ‘the elimination of discrimination against individuals with dis-
abilities.’ ”62

   [14] Thus, on the basis of the plain language of the ADA,
and with the support of seven other circuits, we conclude that
“solely” is not the appropriate causal standard under any of
the ADA’s liability provisions. The next question is what that
proper standard is. We conclude that a motivating factor stan-
dard is the appropriate standard for causation in the ADA con-
text for the reasons discussed below.

   [15] We agree with our sister circuits that a “motivating
factor” standard is most consistent with the plain language of
the statute and the purposes of the ADA.63 Moreover, the
“motivating factor” standard comports with our existing prece-
dent.64 For example, in Hernandez we characterized the bur-
den as proving that “disability actually played a role in the
employer’s decisionmaking process and had a determinative
influence on the outcome.”65 Similarly, in Snead we stated the
causal requirement as demonstrating to the trier of fact that “a
  62
      Id. (quoting 42 U.S.C. § 12101(b)(1)).
  63
      Parker, 204 F.3d at 337 (explaining that removal of the word “solely”
from the causation standard of the ADA, the broad purpose of the ADA,
and the causation standards applicable to Title VII, “suggest[ ] forcefully
that Congress intended the [ADA] to reach beyond the Rehabilitation Act
to cover situations in which discrimination on the basis of disability is one
factor, but not the only factor, motivating an adverse employment
action”); Baird, 192 F.3d at 470; Foster, 168 F.3d at 1033; Katz, 87 F.3d
at 33; Buchanan, 85 F.3d at 200; Pedigo, 60 F.3d at 1301. In McNely, the
Eleventh Circuit described the “because of” standard as conveying in ordi-
nary usage “the idea of a factor that made a difference in the outcome . . .
[—] a ‘but-for’ liability standard.” McNely, 99 F.3d at 1077.
   64
      See, e.g., Hernandez v. Hughes Missile Sys. Co., 362 F.3d 564, 568
(9th Cir. 2004); Snead v. Metro. Prop. & Cas. Ins. Co., 237 F.3d 1080,
1094 (9th Cir. 2001).
   65
      Hernandez, 362 F.3d at 568 (quoting Reeves v. Sanderson Plumbing
Prods., Inc., 530 U.S. 133, 141 (2000)) (internal alterations and quotation
marks omitted) (emphasis added).
7886              HEAD v. GLACIER NORTHWEST, INC.
discriminatory reason more likely motivated the employer.”66
Therefore, we hold that the ADA outlaws adverse employ-
ment decisions motivated, even in part, by animus based on
a plaintiff’s disability or request for an accommodation — a
motivating factor standard. Our next inquiry is how jury
instructions must reflect this causation standard.

       2.   Jury instructions required under the ADA

   Costa explicates the proper approach to formulating jury
instructions in an ADA case:

       Once at the trial stage, the plaintiff is required to put
       forward evidence of discrimination “because of” a
       protected characteristic. After hearing both parties’
       evidence, the district court must decide what legal
       conclusions the evidence could reasonably support
       and instruct the jury accordingly.67

   The Costa court laid out two alternatives for the trial judge.
This approach reflects the fact that although the statute uses
“because of” language, the ADA plaintiff need not show more
than that impermissible motives were a “motivating factor” in
any adverse action. The approach also reflects the fact that the
evidence in a particular case may not suggest more than one
possible reason for the challenged action.
  66
     Snead, 237 F.3d at 1094 (citing Texas Dep’t of Cmty. Affairs v. Bur-
dine, 450 U.S. 248, 256 (1981)).
  67
     299 F.3d at 856. Costa, though a Title VII case, applies equally in the
ADA context. Cf. Hernandez v. Hughes Missile Systs. Co., 362 F.3d 564,
568 (9th Cir. 2004) (drawing on Title VII precedent to set out plaintiff’s
burden in ADA case); Snead v. Metro. Property & Cas. Ins. Co., 237 F.3d
1080, 1093 (9th Cir. 2001) (holding that Title VII analysis applies in ADA
case). See also Baird, 192 F.3d at 470 (holding Title VII causation stan-
dard applicable under the ADA); Foster v. Arthur Andersen, LLP, 168
F.3d 1029, 1033 (7th Cir. 1999) (same).
                    HEAD v. GLACIER NORTHWEST, INC.          7887
   [16] Under the first alternative in Costa, if the judge deter-
mines that the only reasonable conclusion the jury could reach
is that discriminatory animus is the sole reason for the chal-
lenged action or that discrimination played no role in the deci-
sion, the jury should be instructed to determine whether the
challenged action was taken “because of” the prohibited rea-
son.68

   [17] The second alternative applies in a case in which the
evidence could support a finding that discrimination is one of
two or more reasons for the challenged decision, at least one
of which may be legitimate. In that case the jury should be
instructed to determine whether the discriminatory reason was
“a motivating factor” in the challenged action.69

   At issue in this case regarding Head’s discrimination claims
was why Glacier fired him — whether it did so because he
violated the equipment policy, because Glacier perceived him
as being disabled, or because of some combination of the two.
At issue regarding Head’s retaliation claims was whether Gla-
cier fired him because he violated the equipment policy,
because he requested a reasonable accommodation, or
because of some combination of the two. There was evidence
to support a conclusion that each of these reasons had a role
in Head’s discharge.

   [18] Thus, a jury could have found that Head was fired for
violating the equipment abuse policy, because of his per-
ceived disability, or for both reasons. It was error therefore for
the court to refuse to give the requested mixed-motive instruc-
tion.
  68
    299 F.3d at 856.
  69
       Id. at 856-57.
7888               HEAD v. GLACIER NORTHWEST, INC.
       3.   Prejudice

   The district court’s use of “because of” and “because” jury
instructions in this case “does not require reversal if the error
was ‘more probably than not harmless.’ ”70 The harmless error
standard requires error to be proven harmless more probably
than not,71 which in practical effect means that an error is prej-
udicial unless evidence more probably than not proves other-
wise.

   [19] As noted, a jury could have found that Head was fired
for violating the equipment abuse policy, because of his per-
ceived disability, or both. Under the correct causation stan-
dard, the second or third of these findings should have meant
liability for Glacier. But the “because of” instruction given
could have allowed a jury to conclude that Head needed to
show sole causation and thus to deny liability for Glacier even
though the jury had found that both reasons played a role in
motivating Glacier’s discharge of Head. Thus, the instructions
given improperly favored Glacier.

   [20] The record contains no indication that the jury’s ver-
dict was more likely based on the finding that Glacier’s action
was based solely on Head’s performance. Thus, it is not possi-
ble to conclude that the error in instructions was more likely
than not harmless to Head. Because the instructional error
cannot be shown to be harmless, we vacate the jury verdict.

IV.     CONCLUSION

   We conclude that Head has alleged sufficient evidence to
demonstrate a substantial impairment in the established major
life activities of sleeping, interacting with others, and think-
ing. Moreover, Head has alleged sufficient evidence of a sub-
stantial impairment regarding reading and we conclude that
  70
      Mockler, 140 F.3d at 812.
  71
      Id.
                HEAD v. GLACIER NORTHWEST, INC.             7889
reading is a major life activity. Therefore, we reverse the dis-
trict court and remand for a determination on the merits of
Head’s claims based on disability and record of disability.
The district court properly excluded lay witness testimony
because it would not have been helpful to the jury. Finally, we
adopt a “motivating factor” standard for causation in the ADA
context and conclude that the use of “because of” and “be-
cause” instructions in this case was prejudicial. Therefore, we
vacate the jury verdict and remand for further proceedings.

  REVERSED and REMANDED in part, AFFIRMED in
part. Each party shall bear its own costs on appeal.



T.G. NELSON, Circuit Judge, Specially Concurring:

   I concur in the judgment and in all of the court’s opinion
except Note 2 and Part III.B.2. I disagree with the court’s con-
clusion that the district court should choose between a “be-
cause of” instruction or a motivating factor instruction in
ADA cases. That conclusion contradicts our holdings in Part
III.B.1 and Part III.B.3. In addition, it inappropriately imports
a Title VII standard that does not apply in the ADA context.

   In Part III.B.1 we hold that “the ADA outlaws adverse
employment decisions motivated, even in part, by animus
based on a plaintiff’s disability or request for an accommoda-
tion — a motivating factor standard.”1 We also clearly state
that “ ‘solely’ is not the appropriate causal standard under any
of the ADA’s liability provisions.”2 Thus, a plaintiff in an
ADA case is never required to show that impermissible ani-
mus was the sole cause of an adverse employment decision.
The plaintiff need only show that such animus at least par-
tially motivated the employer to make its adverse employment
  1
   Majority Opinion at 7886.
  2
   Id. at 7885.
7890              HEAD v. GLACIER NORTHWEST, INC.
decision. Consequently, any jury instruction that requires a
plaintiff to show that an impermissible animus solely caused
an adverse employment action misstates the law.

   In Part III.B.3 we hold that the district court’s use of “be-
cause of” and “because” jury instructions in this case was
prejudicial because a jury may impermissibly infer a “sole”
causation requirement from a “because of” instruction.3 We
recognize that “the ‘because of’ instruction given [by the dis-
trict court] could have allowed a jury to conclude that Head
needed to show sole causation and thus to deny liability for
Glacier even though the jury had found that both reasons
played a role in motivating Glacier’s discharge of Head.”4
Because the “because of” jury instruction may have caused
Head to have to prove sole causation, it misstated the law.

   The majority’s approach in Part III.B.2 directly contradicts
the holdings described above. It would require the trial court
to give a “because of” instruction if it “determines that the
only reasonable conclusion the jury could reach is that dis-
criminatory animus is the sole reason for the challenged
action or that discrimination played no role in the decision.”5
As we hold in Part III.B.3, such an instruction would imper-
missibly allow jurors to infer a “sole” causation requirement.6
As we hold in part III.B.1, a plaintiff is never required to
establish that discriminatory animus solely caused an adverse
employment decision. Thus, the majority’s approach contra-
dicts the rest of its opinion and mandates the use of a jury
instruction the majority has itself found to be improper.7
  3
     Id. at 7888.
  4
     Id. at 7888.
   5
     Id. at 7887.
   6
     See id. at 7888 (acknowledging that a jury may infer a “sole” causation
requirement from a “because of” instruction).
   7
     See White v. Ford Motor Co., 312 F.3d 998, 1012 (9th Cir. 2002)
(“Jury instructions must fairly and adequately cover the issues presented,
must correctly state the law, and must not be misleading.”). Majority
Opinion at 7888.
                  HEAD v. GLACIER NORTHWEST, INC.                    7891
   The majority arrives at its internally contradictory opinion
because it imports a standard borrowed from Costa v. Desert
Palace, Inc.,8 a Title VII case, that does not apply in the ADA
context. In Costa, we explained that after hearing all the evi-
dence, the district court must choose between a “because of”
and “motivating factor” jury instruction.9 It would choose the
former if “the only reasonable conclusion a jury could reach
is that discriminatory animus is the sole cause for the chal-
lenged employment action or that discrimination played no
role at all in the employer’s decisionmaking.”10 It would
choose the latter if “the evidence could support a finding that
discrimination is one of two or more reasons for the chal-
lenged decision, at least one of which may be legitimate.”11

   The choice of jury instructions makes sense in the Title VII
context. However, it does not make sense to transfer Title
VII’s approach to the choice of jury instructions in an ADA
case.12 Differences in the language and interpretation of the
two statutes requires a choice of jury instructions in the Title
VII context and only one jury instruction in the ADA context:
a motivating factor instruction. Although Title VII and the
ADA both contain “because of” type language for liability,13
Title VII contains additional statutory language about
defenses. Most significantly, Title VII allows for a “same
decision” defense in cases in which the plaintiff argues that
discrimination was not the sole motivation of the employer’s
  8
    299 F.3d 838 (9th Cir. 2002), aff’d 539 U.S. 90 (2003).
  9
    Costa, 299 F.3d at 856.
   10
      Id. (emphasis in original).
   11
      Id. at 857. Despite these differing jury instructions, we emphasized
that regardless of the instruction given, plaintiff’s ultimate burden under
Title VII is to show an adverse employment decision “because of” dis-
crimination. Id.
   12
      Many aspects of the Title VII context do transfer to the ADA context.
See, e.g., Snead v. Metro. Prop. & Cas. Ins. Co., 237 F.3d 1080, 1093 (9th
Cir. 2001).
   13
      See 42 U.S.C. §§ 2000e-2, 12112(a), 12132, 12203(a).
7892                HEAD v. GLACIER NORTHWEST, INC.
adverse action, but only a motivating factor.14 In such cases,
if the jury concludes that the employer would have taken the
same adverse action even without the discriminatory reason,
the employer’s liability is severely curtailed.15 Thus, a plain-
tiff’s decision to establish discrimination as a sole cause or
merely a motivating factor is a significant one in Title VII
cases. Moreover, the language in Title VII drives Costa’s
holding that the court must choose between two alternative
jury instructions depending on the evidence the plaintiff pre-
sented.16 There is no similar language in the ADA. The ADA
does not provide for a “same decision” defense. Neither does
it provide any mechanism for the reduction of damages
depending on whether discriminatory animus motivated the
employer’s action in whole or in part. Finally, we hold today
that plaintiff’s need only ever show that discrimination is a
motivating factor in an ADA case. Accordingly, the rationale
for selecting between jury instructions in a Title VII case is
absent in the ADA context.17
  14
      42 U.S.C. § 2000e-5(g)(2)(B). This section provides:
       On a claim in which an individual proves a violation under sec-
       tion 2000e-2(m) of this title and a respondent demonstrates that
       the respondent would have taken the same action in the absence
       of the impermissible motivating factor, the court —
           (i) may grant declaratory relief, injunctive relief (except as
           provided in clause (ii)), and attorney’s fees and costs demon-
           strated to be directly attributable only to the pursuit of a
           claim under section 2000e-2(m) of this title; and
           (ii) shall not award damages or issue an order requiring any
           admission, reinstatement, hiring, promotion, or payment,
           described in subparagraph (A).
Id.
  15
      Id.
  16
      Id.
   17
      Furthermore, in light of the fact that a plaintiff need only show that
discriminatory animus partially motivated the challenged action, regard-
less of the evidence actually presented, it is a waste of scarce judicial
resources to require district courts to make this unnecessary determination
in an ADA case.
               HEAD v. GLACIER NORTHWEST, INC.           7893
  For these reasons, I cannot join in Note 2 and Part III.B.2
of the majority’s opinion. Under our decision, only a “moti-
vating factor” jury instruction is appropriate in an ADA case.
