                  Rehearing granted, October 24, 2006




                      CORRECTED OPINION
                          PUBLISHED

UNITED STATES COURT OF APPEALS
                FOR THE FOURTH CIRCUIT


DOUGLAS C. SCHULTZ; ANTHONY D.          
PHINIEZY; MELISSA J. LOPES; STEVEN
ROWE; JARED C. BAKER,
               Plaintiffs-Appellants,
                 v.                               No. 05-1192
CAPITAL INTERNATIONAL SECURITY,
INCORPORATED; OUSAMA ALHBRI,
a/k/a Sammy Hebri,
              Defendants-Appellees.
                                        
            Appeal from the United States District Court
         for the Eastern District of Virginia, at Alexandria.
                  Gerald Bruce Lee, District Judge.
                          (CA-04-346-A)

                       Argued: May 24, 2006

                      Decided: October 24, 2006

       Before WILKINS, Chief Judge, and WILLIAMS and
                  MICHAEL, Circuit Judges.



Affirmed in part, vacated in part, and remanded by published opinion.
Judge Michael wrote the opinion, in which Chief Judge Wilkins and
Judge Williams joined.


                             COUNSEL

ARGUED:  Charles    W.    Gilligan,     O’DONOGHUE         &
O’DONOGHUE, Washington, D.C., for Appellants. Haig Vahan Kal-
2            SCHULTZ v. CAPITAL INTERNATIONAL SECURITY
bian, KALBIAN & HAGERTY, L.L.P., Washington, D.C., for
Appellees. ON BRIEF: Francis J. Martorana, Sally M. Tedrow,
O’DONOGHUE & O’DONOGHUE, Washington, D.C., for Appel-
lants. Claire A. DeLelle, KALBIAN & HAGERTY, L.L.P., Washing-
ton, D.C., for Appellees.


                              OPINION

MICHAEL, Circuit Judge:

   Prince Faisal bin Turki bin Nasser Al-Saud (the Prince) is a diplo-
mat and a member of the Saudi royal family. The Prince, who has a
residence in McLean, Virginia, engaged Capital International Secur-
ity, Inc. (CIS) to provide a personal security detail. Five of the agents
who worked on the Prince’s detail sued CIS and its president, Sammy
Hebri, asserting claims for unpaid overtime under the Fair Labor
Standards Act, 29 U.S.C. §§ 201-219 (FLSA or Act). After a bench
trial the district court entered judgment for CIS and Hebri, holding
that the agents were not entitled to overtime pay because they were
independent contractors, not employees. The agents appeal, and we
vacate the judgment in favor of the defendants and remand the case
for further proceedings on the overtime claim. The undisputed facts
compel the legal conclusion that the Prince and CIS were joint
employers and that the agents were their employees for purposes of
the FLSA. CIS will be jointly and severally liable on remand for the
payment of any overtime required by the FLSA during the agents’
employment. Hebri is also alleged to be an employer, and the district
court should make a determination with respect to his status and lia-
bility, if any. We affirm the evidentiary rulings challenged by two of
the agents.

                                   I.

  The facts in this case are essentially undisputed. The following
account is based on the district court’s findings and other uncontro-
verted facts established at trial. The plaintiffs, Douglas Schultz,
Anthony Phiniezy, Melissa Lopes, Steven Rowe, and Jared Baker,
were "personal protection specialists" (PPS agents) licensed by the
              SCHULTZ v. CAPITAL INTERNATIONAL SECURITY                  3
Virginia Department of Criminal Justice Services (VDCJS). Licensed
PPS agents "engage[ ] in the duties of providing close protection from
bodily harm to any person." Va. Code Ann. § 9.1-138. A PPS agent
may operate his own security business in Virginia if he obtains a pri-
vate security business license from the VDCJS. Id. § 9.1-139(A).
Although all five plaintiffs had at some point obtained individual PPS
licenses, none of them had the additional license required to operate
a security business.

   The plaintiff-agents provided security services for the Prince and
his family at the Prince’s Virginia residence in twelve-hour shifts.
The agents were paid a daily rate for each shift; they received no extra
pay for overtime. The agents had a command post at the residence,
from which they observed security camera monitors, answered the
telephone, and kept a daily log of all arrivals and departures. They
also made hourly walks of the property, ensured that members of the
Prince’s family were safe when departing and arriving, sorted mail,
and performed various tasks upon request of the Prince’s family. In
addition to their security duties, the agents were responsible for hav-
ing the household’s vehicles washed and fueled, making wake up
calls, moving furniture, and doing research on the Internet. Although
the nature of the work the agents performed for the Prince remained
more or less the same throughout their employment, certain facts
bearing on whether they were employees or independent contractors
changed over time.

   In 1998 a company called Vance International, Inc. (Vance) sup-
plied the Prince’s security detail. Vance submitted bills for its ser-
vices to the Saudi Embassy, which paid for the Prince’s detail because
he was a diplomat representing the Royal Kingdom of Saudi Arabia.
From the beginning, plaintiffs Schultz and Phiniezy worked for Vance
on the Prince’s detail. The other three plaintiffs joined the detail later,
sometime between 1998 and 2002. Vance trained the agents assigned
to the detail and helped them obtain their Virginia PPS licenses. The
detail was led by two men: a Vance employee named Randy Parham
and an employee of the Prince, Sami Abushalback. Abushalback, a
former Vance employee, was the Prince’s head of security and per-
sonal secretary. During the time Vance was involved with the detail,
Parham and Abushalback drafted a document called the Standard
Operating Procedure (SOP), which specified how the detail would
4            SCHULTZ v. CAPITAL INTERNATIONAL SECURITY
operate. Vance representatives visited the detail on site each month
to perform an audit. Vance also randomly removed agents from the
detail and assigned them to serve other Vance clients.

   In 1998 the Prince and Abushalback decided to terminate Vance’s
services. The Prince became unhappy with Vance because it changed
agents frequently, exercised too much control over the agents, and
wanted too many reports. After the decision to terminate Vance, Abu-
shalback approached Parham, Phiniezy, Schultz, and two other Vance
employees and asked them if they would continue working for the
Prince under a new company, FAM International (FAM). The agents
agreed. Because the agents had each signed a non-competition agree-
ment with Vance, the company sued and obtained an injunction. The
Prince contributed between $50,000 and $60,000 to settle the case. He
also paid each agent $1,000 because none of them could work during
the litigation. Once FAM took over the detail, Abushalback exercised
more control over the agents.

   In July 2002 the Prince terminated FAM’s contract because FAM
could not float the funds to meet its biweekly payroll obligations
while awaiting payment from the Saudi Embassy. Around this time,
the Prince’s long-time driver and travel agent, Sammy Hebri, formed
a company called Capital International Security, Inc. (CIS). Hebri
started CIS for the purpose of replacing FAM as the Prince’s security
contractor. Hebri had no prior experience in the private security busi-
ness. Abushalback negotiated an oral contract with Hebri for CIS to
administer the detail. CIS had virtually no involvement in the detail’s
day-to-day operations. In fact, when CIS took over the detail, neither
CIS nor Hebri was given a copy of the detail’s SOP. Parham, who
was the detail leader throughout the transition period, reported to
Abushalback. With Parham’s input, Abushalback decided each
agent’s work assignments. Parham did, however, send CIS approxi-
mately seventeen status reports on detail operations and issues
between July 2002 and the filing of this lawsuit in March 2004.

  CIS was involved to a degree in the detail’s personnel matters. CIS
helped recruit new agents by placing advertisements in newspapers
and screening resumes for applicants with PPS licenses. CIS for-
warded screened resumes to Parham, but it did not interview appli-
cants or otherwise participate in hiring decisions. Parham reviewed
              SCHULTZ v. CAPITAL INTERNATIONAL SECURITY                  5
the selected resumes and conducted interviews. Abushalback had the
final say on hiring, though he usually deferred to Parham. Parham
notified CIS when a new agent was hired, and CIS then added the per-
son to payroll. When Parham, the detail leader, resigned in January
2004, Abushalback chose the new leader, Bob Hillyard, without input
from CIS.

   Abushalback generally handled scheduling, compensation levels,
discipline, and termination of detail members, although CIS also
played a limited role in these matters. For instance, in April 2003 the
agents requested a meeting with Hebri to discuss their pay rate. Hebri
raised the pay issue with Abushalback, who told Hebri that there was
"no need for anybody to have anything." J.A. 439. CIS then sent a let-
ter to the agents explaining that "due to circumstances beyond the
control of [CIS], [the company] will not be able to discuss pay raises
until January 2004." J.A. 81. Also, in March 2004 Hebri sent a memo
to the agents threatening disciplinary action against any agent found
carrying a firearm he was not trained to use. CIS and the Prince both
provided equipment to the detail. Although most detail members car-
ried their own personal handguns, CIS provided handguns for those
agents who did not carry their own. CIS also provided the agents with
radios, holsters, first aid kits, business cards, and lapel pins, while the
Prince provided cars, cameras, cell phones, and office supplies.

   Shortly after CIS replaced FAM, Hebri sent a memo (dated July
24, 2002) to the agents directing them to obtain their own private
security business licenses from the VDCJS and individual liability
insurance so they could be classified as independent contractors. The
memo explained, "If the agent does not have these licenses [he]
would have to be hired as an employee . . . . Employees would come
under the liability coverage and business license of [CIS]." J.A. 79.
In follow-up letters to the agents on July 25, Hebri added that detail
members must secure the licenses and liability insurance (in other
words, "have independent contractor status") by September 1, 2002,
or "be relieved of duty" from the detail. J.A. 80. Schultz, who had
allowed his PPS license to expire, brought these communications to
Abushalback because he was concerned about losing his job. Abu-
shalback told Schultz that he had nothing to worry about because
Hebri was just "trying to cover his butt." J.A. 278. Schultz disre-
garded the warnings. CIS did not enforce the licensing and insurance
6            SCHULTZ v. CAPITAL INTERNATIONAL SECURITY
requirements for the next fourteen months, though Hebri asked
Parham periodically whether the agents were taking steps to comply.

   In January 2004 the VDCJS audited CIS’s operations. In the face
of the audit, Hebri again informed the agents that those without indi-
vidual business licenses and liability insurance would be reclassified
as employees and paid an hourly rate. Hebri also said that those not
meeting the requirements would have to sign employee agreements
setting forth new hourly rates or be removed from the detail. Plaintiffs
Lopes and Rowe had resigned months earlier, but Schultz, Phiniezy,
and Baker were still working on the detail and had not obtained the
business licenses or insurance. Phiniezy and Baker signed employee
agreements that decreased their rate of pay, though their duties did not
change. Schultz, who lacked a current PPS license, was reclassified
as an "alarm responder" and his pay was decreased. J.A. 95. The latter
three agents all resigned within a short time.

   On March 29, 2004, the five plaintiffs sued CIS and Hebri for
unpaid overtime under the FLSA. See 29 U.S.C. § 207(a)(2). After the
lawsuit was filed, plaintiffs Phiniezy and Baker relocated to Iraq to
work for private security contractors. At the time of their departure,
Phiniezy had already given a deposition, but Baker had not. The
defendants moved to compel Baker to appear for a deposition, and a
magistrate judge ordered him to participate in a telephonic deposition
and to appear in person for a deposition at least 48 hours before trial.
Although Baker gave a telephonic deposition (not under oath) from
Iraq, he did not appear in person for a pretrial deposition. Neither
Baker nor Phiniezy appeared at trial. About a week before trial, the
defendants filed a motion to compel Baker’s deposition or, in the
alternative, to dismiss Phiniezy’s and Baker’s claims for failure to
prosecute. The court denied the defendants’ motion to dismiss, but
ruled that Baker and Phiniezy could not offer evidence at trial. It
appears that the court enforced these rulings not only by excluding
Baker’s and Phiniezy’s depositions, but also by considering the evi-
dence admitted as applying to the claims of all plaintiffs.

   The defendants’ sole defense at trial was that the agents were not
covered by the FLSA because they were independent contractors, not
employees as defined by the Act. After a three-day bench trial, the
district court ruled against the plaintiffs, holding that they were inde-
             SCHULTZ v. CAPITAL INTERNATIONAL SECURITY                7
pendent contractors, and entered judgment in favor of CIS and Hebri.
This appeal followed.

                                  II.

   The agents contend that the undisputed facts compel the legal con-
clusion that they were employees, not independent contractors. The
ultimate conclusion as to whether a worker is an employee or inde-
pendent contractor under the FLSA presents a legal question that we
review de novo. Brock v. Mr. W Fireworks, Inc., 814 F.2d 1042,
1044-45 (5th Cir. 1987); cf. Icicle Seafoods, Inc. v. Worthington, 475
U.S. 709, 713-14 (1986) (observing that the determination of whether
an employee falls within the scope of a FLSA exemption is ultimately
a legal question); Walton v. Greenbrier Ford, Inc., 370 F.3d 446, 450
(4th Cir. 2004) (same).

   The FLSA was enacted to protect "the rights of those who toil, of
those who sacrifice a full measure of their freedom and talents to the
use and profit of others." Benshoff v. City of Virginia Beach, 180 F.3d
136, 140 (4th Cir. 1999) (quoting Tenn. Coal, Iron & R.R. Co. v.
Muscoda Local No. 123, 321 U.S. 590, 597 (1944)). "[B]ecause the
Act is remedial and humanitarian in purpose, it should be broadly
interpreted and applied to effectuate its goals." Id. (internal citation
and quotation marks omitted). The FLSA, in addition to mandating a
minimum wage for covered employees, requires the payment of over-
time for each hour worked in excess of forty per work week. 29
U.S.C. §§ 206(a)(1), 207 (a)(1).

   An employee is defined as "any individual employed by an
employer," id. § 203(e)(1), and an "employer" includes "any person
acting directly or indirectly in the interest of an employer in relation
to an employee," id. § 203(d). In addition, the Act "defines the verb
‘employ’ expansively to mean ‘suffer or permit to work.’" Nation-
wide Mut. Ins. Co. v. Darden, 503 U.S. 318, 326 (1992) (quoting 29
U.S.C. § 203(g)). These definitions broaden "the meaning of
‘employee’ to cover some [workers] who might not qualify as such
under a strict application of traditional agency [or contract] law prin-
ciples." Id. In determining whether a worker is an employee covered
by the FLSA, a court considers the "economic realities" of the rela-
tionship between the worker and the putative employer. Henderson v.
8             SCHULTZ v. CAPITAL INTERNATIONAL SECURITY
Inter-Chem Coal Co., 41 F.3d 567, 570 (10th Cir. 1994) (citing Bar-
tels v. Birmingham, 332 U.S. 126, 130 (1947)). The focal point is
whether the worker "is economically dependent on the business to
which he renders service or is, as a matter of economic [reality], in
business for himself." Id. (internal quotation marks and alteration
omitted); see also Martin v. Selker Bros., Inc., 949 F.2d 1286, 1293
(3d Cir. 1991); Brock v. Superior Care, Inc., 840 F.2d 1054, 1059 (2d
Cir. 1988); Usery v. Pilgrim Equip. Co., 527 F.2d 1308, 1311 (5th
Cir. 1976).

   The emphasis on economic reality has led courts to develop and
apply a six-factor test to determine whether a worker is an employee
or an independent contractor. The factors are (1) the degree of control
that the putative employer has over the manner in which the work is
performed; (2) the worker’s opportunities for profit or loss dependent
on his managerial skill; (3) the worker’s investment in equipment or
material, or his employment of other workers; (4) the degree of skill
required for the work; (5) the permanence of the working relationship;
and (6) the degree to which the services rendered are an integral part
of the putative employer’s business. Herman v. Mid-Atlantic Installa-
tion Servs., Inc., 164 F. Supp. 2d 667, 671 (D. Md. 2000); see also
Henderson, 41 F.3d at 570. (These factors are often called the "Silk
factors" in reference to United States v. Silk, 331 U.S. 704 (1947), the
Supreme Court case from which they derive.) No single factor is dis-
positive; again, the test is designed to capture the economic realities
of the relationship between the worker and the putative employer.
Henderson, 41 F.3d at 570.

   Applying the Silk test, the district court concluded that the agents
were independent contractors, not FLSA-covered employees. The dis-
trict court’s analysis focused primarily on the first Silk factor, and the
analysis compared the minimal control CIS had over the agents with
the high degree of control exercised by the Prince. Although control
is an important part of the Silk test, the issue is not the degree of con-
trol that an alleged employer has over the manner in which the work
is performed in comparison to that of another employer. Rather, it is
the degree of control that the alleged employer has in comparison to
the control exerted by the worker. The district court therefore erred
by weighing the degree of control exercised by CIS against that exer-
cised by the Prince. The court should have instead weighed the
             SCHULTZ v. CAPITAL INTERNATIONAL SECURITY                 9
agents’ control against the total control exercised by CIS and the
Prince. In taking this wrong turn, the district court strayed from the
ultimate question posed by the Silk test: whether the agents were, as
a matter of economic reality, dependent on the business they served,
or, conversely, whether they were in business for themselves. See
Bartels, 332 U.S. at 130; Henderson, 41 F.3d at 570. Before the Silk
test can be correctly applied in this case, the established facts must be
reviewed to identify the putative employer or employers. As the dis-
cussion below reveals, CIS and the Prince were joint employers who
must be viewed as providing "one employment" for purposes of the
FLSA. When the Silk test is applied to this joint employment arrange-
ment, the inescapable legal conclusion is that the agents were employ-
ees, not independent contractors.

                                   A.

   Separate persons or entities that share control over an individual
worker may be deemed joint employers under the FLSA. According
to the Department of Labor regulation:

    if the facts establish that the employee is employed jointly
    by two or more employers, i.e., that employment by one
    employer is not completely disassociated from employment
    by the other employer(s), all of the employee’s work for all
    of the joint employers during the workweek is considered as
    one employment for purposes of the [FLSA].

29 C.F.R. § 791.2(a) (emphasis added); see also Falk v. Brennan, 414
U.S. 190, 195 (1973) (observing in a FLSA case that apartment build-
ing maintenance workers were employed by both building manage-
ment company and building owners). "[A]ll joint employers are
responsible, both individually and jointly, for compliance with all of
the applicable provisions of the [FLSA], including the overtime provi-
sions." 29 C.F.R. § 791.2(a). The regulation states that "a joint
employment relationship generally will be considered to exist in situ-
ations such as:"

       (1) Where there is an arrangement between the employ-
    ers to share the employee’s services, as, for example, to
    interchange employees; or
10            SCHULTZ v. CAPITAL INTERNATIONAL SECURITY
         (2) Where one employer is acting directly or indirectly in
      the interest of the other employer (or employers) in relation
      to the employee; or

         (3) Where the employers are not completely disassoci-
      ated with respect to the employment of a particular
      employee and may be deemed to share control of the
      employee, directly or indirectly, by reason of the fact that
      one employer controls, is controlled by, or is under common
      control with the other employer.

29 C.F.R. § 791.2(b) (footnotes omitted). The joint employment
inquiry must "take[ ] into account the real economic relationship
between the employer who uses and benefits from the services of
workers and the party that hires or assigns the workers to that
employer." Ansoumana v. Gristede’s Operating Corp., 255 F. Supp.
2d 184, 193 (S.D.N.Y. 2003); see also Baystate Alternative Staffing,
Inc. v. Herman, 163 F.3d 668, 674-76 (1st Cir. 1998); Bonnette v.
Calif. Health & Welfare Agency, 704 F.2d 1465, 1469-70 (9th Cir.
1983). The ultimate determination of joint employment must be based
upon the "circumstances of the whole activity." Bonnette, 704 F.2d at
1470.

   The undisputed facts in this case show that CIS and the Prince were
joint employers of the agents.1 The agents performed work "which
simultaneously benefit[ted]" both CIS and the Prince. 29 C.F.R.
§ 791.2(b). Moreover, the entire employment arrangement fits
squarely within the third example of joint employment in the regula-
tion: the Prince and CIS were "not completely disassociated with
respect to the employment of [the agents]," and the Prince "share[d]
control of the [agents]" with CIS. Id. § 791.2(b)(3). Both the Prince
and CIS were involved in the hiring of agents, although the Prince
(through Abushalback) exercised a greater degree of authority. CIS
advertised for agents and screened responses, which were forwarded
to the detail leader. The detail leader, who was on the CIS payroll and
reported to Abushalback, interviewed selected applicants; Abushal-
  1
  We recognize that in certain cases it may be necessary to first deter-
mine whether a party is an "employer" for FLSA purposes before deter-
mining whether a joint employment arrangement exists.
              SCHULTZ v. CAPITAL INTERNATIONAL SECURITY                11
back had the final word on hiring. Abushalback generally handled
agent work schedules, compensation, discipline, and terminations, but
CIS played some role in these matters. CIS maintained the authority
to discipline agents and change the terms of their employment. For
example, CIS warned the agents in writing that "disciplinary action
[would] be instituted" by the company against any agent who carried
a firearm he was "not trained on." J.A. 115. In one instance an agent
discussed his concerns about CIS’s new licensing and insurance
requirements with Abushalback, who told the agent he had nothing to
worry about. However, when this agent failed to comply with the
requirements, CIS eventually demoted him and cut his pay. In addi-
tion, the Prince and CIS shared responsibility for supplying the agents
with equipment.2

                                   B.

   Because CIS and the Prince were joint employers of the agents, the
employment arrangement must be viewed as "one employment" for
purposes of determining whether the agents were employees or inde-
pendent contractors under the FLSA. See 29 C.F.R. § 791.2(a). The
district court therefore should have focused its Silk inquiry on the one
employment provided jointly by the Prince and CIS. The one-
employment focus leads to a proper determination of whether, as a
matter of economic reality, the agents were dependent on the joint
employers or whether they were in business for themselves. See Bar-
tels, 332 U.S. at 130; Henderson, 41 F.3d at 570. When the undis-
puted facts are examined using this correct legal framework, it
becomes evident that the agents were FLSA-covered employees, not
independent contractors.

  2
    Again, the undisputed facts here fit readily within the third example
of joint employment listed in the regulation. See 29 C.F.R. § 791.2(b)(3).
In some cases it may be useful for a court to consider factors such as
those listed in Bonnette, 704 F.2d at 1469-70, and Zheng v. Liberty
Apparel Co., Inc., 355 F.3d 61, 71-72 (2d Cir. 2003), in determining
whether there are joint employers within the meaning of the Act and the
regulation.
12           SCHULTZ v. CAPITAL INTERNATIONAL SECURITY
                                   1.

   The first Silk factor is the degree of control that the putative
employer has over the manner in which the work is performed. When
the employment arrangement here is considered as one employment
by the Prince (acting through Abushalback) and CIS, the joint
employers exercised nearly complete control over how the agents did
their jobs. The eight-page SOP — written and issued by Abushalback
and the detail leader — strictly dictated the manner in which the
agents were to carry out their duties of providing security for the
Prince and his family. For instance, the SOP directed agents to
"[m]ake hourly walks" of the property, J.A. 72, to "make regular
checks at all locations where contractors are working," J.A. 74, and
to escort contractors in and out of the residence through a specific set
of doors. The SOP even dictated the exact manner in which the agents
were to open the front door of the residence when the Prince arrives:
"[The agent] will open the door for Prince Faisal (if he is alone) or
for Princess Reema if they are together and have no security with
them. If security is with them then the outside agent will open the
door for Prince Faisal and leave the door for Princess Reema to be
opened by the security agent that is with them." J.A. 73. While there
were no doubt occasions when the agents were required to exercise
independent judgment (such as determining whether a particular visi-
tor appeared suspicious), as a general rule they did not control the
manner in which they provided security.

                                   2.

   The second Silk factor is whether the worker has opportunities for
profit or loss dependent on his managerial skill. In determining that
this factor weighed against finding employee status, the district court
offered reasoning that does not support its ultimate conclusion:

     The number of hours that these individuals worked on the
     detail depended upon the shift. The shift schedule was
     developed by Mr. Parham [the detail leader] after consulting
     with the agents. Mr. Parham and Mr. Abushalback made
     judgments about who would travel overseas. But again
     whether or not a person participated in the schedule,
             SCHULTZ v. CAPITAL INTERNATIONAL SECURITY              13
    whether it was one day or every day depended in part upon
    their desire, availability and the need.

J.A. 522. Agents who were assigned to travel duty were often given
cash bonuses, gifts, or days off with pay. The receipt of these perqui-
sites did not depend on managerial skill, however. There is no evi-
dence the agents could exercise or hone their managerial skill to
increase their pay. CIS paid the agents a set rate for each shift
worked. The Prince’s schedule and security needs dictated the number
of shifts available and the hours worked. There was no way an agent
could finish a shift more efficiently or quickly in order to perform
additional paid work. Cf. Herman, 164 F. Supp. 2d at 674 (noting that
cable installers can control their own profits and losses "by improving
their technique so that they can service more customers faster"). The
agents’ security work was, by its very nature, time oriented, not proj-
ect oriented. The second Silk factor weighs in favor of employee sta-
tus for the agents.

                                  3.

   The third factor is the worker’s investment in equipment or materi-
als required for the task, or his employment of other workers. This
factor weighs heavily against a conclusion that the agents were inde-
pendent contractors. CIS and the Prince supplied almost every piece
of equipment the agents used: radios, holsters, cell phones, cars, cam-
eras, first aid kits, business cards, and lapel pins. Although some
agents chose to use their own firearms, CIS supplied firearms to those
who wanted them. The agents were thus not required to invest in any
equipment or materials. In addition, the agents could not hire other
workers to help them do their work.

   Although the agents arguably had an investment in their individual
PPS licenses, this investment is immaterial for our purposes. Licens-
ing is required of all persons working as personal protection special-
ists in Virginia regardless of whether they are employees or
independent contractors. More telling is the licensing and insurance
that the five plaintiff-agents did not obtain, despite CIS’s flaccid
requests: the individual business licenses and individual liability
insurance. Because the agents were never compelled to obtain these
credentials while they worked on the Prince’s security detail, they
14            SCHULTZ v. CAPITAL INTERNATIONAL SECURITY
continued to operate under the authority of CIS’s license and the pro-
tection of the company’s liability insurance.

                                    4.

   The fourth Silk factor is the degree of skill required for the work.
In concluding that this factor weighed against employee status, the
district court said, "I think that personal security requires special
skills." J.A. 523. This observation cannot end the inquiry, however,
because it applies to many workers, regardless of whether they are
independent contractors or employees. Of course, a licensed PPS
agent can be expected to offer more specialized services than the
average private security guard, and providing security for a diplomat
and members of a royal family surely presents special challenges.
Although these points could weigh in favor of concluding that the
agents were independent contractors, there are important countervail-
ing factors. The agents’ tasks were, for the most part, carefully
scripted by the SOP. Moreover, many of their tasks required little
skill, for example, sorting the mail, making wake up calls, moving
furniture, providing newspapers for the Prince, and checking the Dal-
las Morning News website for updates about the Dallas Cowboys.
Although we are mindful of the district court’s observation about the
need for special skills, we do not see the skill factor as tipping signifi-
cantly one way or the other.

                                    5.

   The fifth factor is the degree of permanency of the working rela-
tionship. The more permanent the relationship, the more likely the
worker is to be an employee. As to this factor the district court noted
only that the real working relationship here was with the Prince, not
CIS. Indeed, when the Prince is viewed as one of the joint employers,
this factor weighs heavily in favor of a conclusion that the agents
were employees. Two of the five plaintiffs began working on the
Prince’s detail in 1998, when Vance had the contract. These agents
chose to stay after the Prince terminated his contract with Vance, even
though their decision exposed them to liability under the non-compete
agreements they had signed with Vance. The Prince contributed
money to settle Vance’s lawsuit against the agents, and he compen-
sated the agents for their lost earnings. More important, the Prince ter-
             SCHULTZ v. CAPITAL INTERNATIONAL SECURITY                15
minated Vance in part because it changed agents too often. When CIS
took over the detail, it hired the agents who were already working on
the Prince’s detail. The Prince clearly wanted security agents who
would be with him over the long term, and CIS worked to oblige the
Prince in this regard.

                                   6.

   The sixth (and last) Silk factor is the extent to which the service
rendered by the worker is an integral part of the putative employer’s
business. CIS was formed specifically for the purpose of supplying
the Prince’s security detail, which appears to have been CIS’s only
business function during the period relevant to this case. The agents
were thus an integral part of CIS’s business. Insofar as the "business"
of the Prince’s residence can be characterized as general housekeep-
ing, the agents’ service was likewise integral. The agents ensured the
safety of the Prince and his family and guests and performed adminis-
trative and personal tasks that no doubt helped the household run
smoothly.

    In sum, the district court committed legal error by applying the Silk
test without first determining whether a joint employment relationship
existed. The undisputed facts establish that CIS and the Prince were
joint employers: the agents performed work that simultaneously bene-
fitted CIS and the Prince, who shared control over the agents’ work.
When the Silk factors are applied to the joint employment circum-
stance, it becomes apparent that the agents were not in business for
themselves. The agents were thus employees, not independent con-
tractors.

                                  III.

   Plaintiffs Baker and Phiniezy, who did not appear for trial, argue
that the district court erred in ruling that they could not offer evi-
dence. When the district court made this ruling at the beginning of
trial, it was faced with conflicting motions from the parties. The
defendants had moved to compel Baker’s deposition or, in the alterna-
tive, to dismiss Baker’s and Phiniezy’s claims for failure to prosecute.
Plaintiffs’ counsel, in turn, had moved to admit excerpts of Baker’s
and Phiniezy’s depositions. Although the court’s ruling that Baker
16            SCHULTZ v. CAPITAL INTERNATIONAL SECURITY
and Phiniezy could not present evidence was stated in broad terms,
the court pointedly denied the motion to dismiss the claims of these
two plaintiffs.

   The court specifically refused to allow plaintiffs’ counsel to intro-
duce excerpts of Baker’s telephonic, unsworn deposition on the
ground that he had violated the magistrate judge’s order by failing to
appear for a live deposition immediately before trial. The court also
precluded plaintiffs’ counsel from offering excerpts of Phiniezy’s
deposition on the ground that Phiniezy made a "deliberate judgment"
not to return to court for trial. J.A. 206; see Fed. R. Civ. P.
32(a)(3)(B) ("The deposition of a witness, whether or not a party, may
be used by any party for any purpose if the court finds . . . that the
witness . . . is out of the United States, unless it appears that the
absence of the witness was procured by the party offering the deposi-
tion."). We review a district court’s evidentiary rulings for abuse of
discretion. United States v. Hodge, 354 F.3d 305, 312 (4th Cir. 2004).
An evidentiary ruling that is an abuse of discretion is reversible only
if it affects a party’s substantial rights. See Fed. R. Evid. 103(a).

   These evidentiary rulings were not an abuse of discretion. As the
district court observed, Baker and Phiniezy were aware of the trial
date but made a conscious decision not to appear. But even if the rul-
ings had been an abuse of discretion, we would not reverse because
the nonattending plaintiffs fail to show that any error affected their
substantial rights. The district court noted at the outset of its findings
and conclusions that "the question presented is whether or not" the
five plaintiffs, including Baker and Phiniezy, were employees under
the FLSA and therefore entitled to overtime. J.A. 486. The district
court decided only the liability issue, but on that issue all five plain-
tiffs received the same consideration with respect to the admitted evi-
dence. This treatment is consistent with the district court’s refusal to
dismiss Baker’s and Phiniezy’s claims on account of their nonatten-
dance. It also appears that the district court admitted some evidence
relevant to the overtime or damages claimed by Baker and Phiniezy.
Courts have, of course, "frequently granted back wages under the
FLSA to non-testifying employees based upon the representative tes-
timony of a small percentage of the employees." Donovan v. Bel-Loc
Diner, Inc., 780 F.2d 1113, 1116 (4th Cir. 1985). We do not interpret
the district court’s evidentiary rulings to preclude an award of over-
              SCHULTZ v. CAPITAL INTERNATIONAL SECURITY                17
time (or damages) to Baker and Phiniezy, if the amounts can be reli-
ably calculated based on evidence admitted without qualification at
trial. In any event, the district court’s evidentiary rulings with respect
to Baker and Phiniezy are affirmed to the extent they were enforced
during trial.

                                   IV.

   The five plaintiff-agents were employees under the FLSA. Because
defendant CIS was one of their joint employers along with the Prince,
CIS is jointly and severally liable for the payment of any overtime
required by the FLSA during the agents’ employment. Accordingly,
we vacate the judgment entered in favor of defendants CIS and
Sammy Hebri and remand the case for further proceedings consistent
with this opinion. We offer no opinion as to the liability of Hebri,
who is also alleged to be an employer. A determination with respect
to Hebri’s status and liability, if any, should be made by the district
court in the first instance. We affirm the district court’s evidentiary
rulings challenged by plaintiffs Baker and Phiniezy.

                                                 AFFIRMED IN PART,
                                                  VACATED IN PART,
                                                    AND REMANDED
