(Slip Opinion)              OCTOBER TERM, 2014                                       1

                                       Syllabus

         NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
       being done in connection with this case, at the time the opinion is issued.
       The syllabus constitutes no part of the opinion of the Court but has been
       prepared by the Reporter of Decisions for the convenience of the reader.
       See United States v. Detroit Timber & Lumber Co., 

, 337.


SUPREME COURT OF THE UNITED STATES

                                       Syllabus

                          WARGER v. SHAUERS

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
                 THE EIGHTH CIRCUIT

   No. 13–517.      Argued October 8, 2014—Decided December 9, 2014
Petitioner Gregory Warger sued respondent Randy Shauers in federal
  court for negligence for injuries suffered in a motor vehicle accident.
  After the jury returned a verdict for Shauers, one of the jurors con-
  tacted Warger’s counsel, claiming that Regina Whipple, the jury fore-
  person, had revealed during deliberations that her daughter had
  been at fault in a fatal motor vehicle accident, and that a lawsuit
  would have ruined her daughter’s life. Armed with an affidavit from
  the juror, Warger moved for a new trial, arguing that Whipple had
  deliberately lied during voir dire about her impartiality and ability to
  award damages. The District Court denied Warger’s motion, holding
  that Federal Rule of Evidence 606(b), which bars evidence “about any
  statement made . . . during the jury’s deliberations,” barred the affi-
  davit, and that none of the Rule’s three exceptions, see Rule
  606(b)(2), were applicable. The Eighth Circuit affirmed.
Held:
    1. Rule 606(b) applies to juror testimony during a proceeding in
 which a party seeks to secure a new trial on the ground that a juror
 lied during voir dire. Pp. 3–10.
       (a) This reading accords with the plain meaning of Rule 606(b),
 which applies to “an inquiry into the validity of [the] verdict.” This
 understanding is also consistent with the underlying common-law
 rule on which Congress based Rule 606(b). The so-called “federal
 rule” made jury deliberations evidence inadmissible even if used to
 demonstrate dishonesty during voir dire. Both the majority of courts
 and this Court’s pre-Rule606(b) cases, see McDonald v. Pless, 

, 268; Clark v. United States, 

, favored this rule
 over the “Iowa rule,” which permitted the use of such jury delibera-
 tions evidence. The federal approach is clearly reflected in the lan-
2                          WARGER v. SHAUERS

                                  Syllabus

    guage Congress chose when it enacted Rule 606(b), and legislative
    history confirms that Congress’ choice was no accident. See Tanner
    v. United States, 

, 125. Pp. 3–8.
          (b) Warger’s arguments against this straightforward understand-
    ing are not persuasive. Pp. 8–10.
            (1) First, Warger insists that proceedings for a new trial based
    on voir dire dishonesty do not involve an “inquiry into the validity of
    the verdict.” His reading would restrict Rule 606(b)’s application to
    claims of error for which a court must examine the manner in which
    the jury reached its verdict, but the Rule does not focus on the means
    by which deliberations evidence might be used to invalidate a verdict.
    It simply applies during a proceeding in which a verdict may be ren-
    dered invalid. Pp. 8–9.
            (2) Warger also contends that excluding jury deliberations evi-
    dence that shows voir dire dishonesty is unnecessary to fulfill Con-
    gress’ objectives, but his arguments would apply to all evidence ren-
    dered inadmissible by Rule 606(b), and he cannot escape the scope of
    the Rule merely by asserting that Congress’ concerns were misplaced.
    P. 9.
            (3) Finally, Warger invokes the canon of constitutional avoid-
    ance, contending that only his interpretation protects the right to an
    impartial jury. But that canon has no application here, where there
    is no ambiguity. See United States v. Oakland Cannabis Buyers’ Co-
    operative, 

, 494. Moreover, this Court’s Tanner decision
    forecloses any claim that Rule 606(b) is unconstitutional. Similar to
    the right at issue in that case, Warger’s right to an impartial jury
    remains protected despite Rule 606(b)’s removal of one means of en-
    suring unbiased jurors. Even if a juror lies to conceal bias, parties
    may bring to the court’s attention evidence of bias before the verdict
    is rendered and use nonjuror evidence after the verdict is rendered.
    Pp. 9–10.
       2. The affidavit at issue was not admissible under Rule
    606(b)(2)(A)’s exception for evidence of “extraneous prejudicial infor-
    mation.” Generally speaking, extraneous information derives from a
    source “external” to the jury. See 

. Here,
    the excluded affidavit falls on the “internal” side. Warger contends
    that any information Whipple shared with the other jurors was ex-
    traneous because she would have been disqualified from the jury had
    she disclosed her daughter’s accident. However, such an exception
    would swallow up much of the rest of the restrictive version of the
    common-law rule that Congress adopted in enacting Rule 606(b).
    Pp. 11–13.

, affirmed.

    SOTOMAYOR, J., delivered the opinion for a unanimous Court.
                       Cite as: 574 U. S. ____ (2014)                              1

                            Opinion of the Court

    NOTICE: This opinion is subject to formal revision before publication in the
    preliminary print of the United States Reports. Readers are requested to
    notify the Reporter of Decisions, Supreme Court of the United States, Wash-
    ington, D. C. 20543, of any typographical or other formal errors, in order
    that corrections may be made before the preliminary print goes to press.


SUPREME COURT OF THE UNITED STATES
                                  _________________

                                  No. 13–517
                                  _________________


  GREGORY P. WARGER, PETITIONER v. RANDY D.

                 SHAUERS

 ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 

           APPEALS FOR THE EIGHTH CIRCUIT

                             [December 9, 2014]


  JUSTICE SOTOMAYOR delivered the opinion of the Court.
  Federal Rule of Evidence 606(b) provides that certain
juror testimony regarding what occurred in a jury room is
inadmissible “[d]uring an inquiry into the validity of a
verdict.” The question presented in this case is whether
Rule 606(b) precludes a party seeking a new trial from
using one juror’s affidavit of what another juror said in
deliberations to demonstrate the other juror’s dishonesty
during voir dire. We hold that it does.
                              I
  Petitioner Gregory Warger was riding his motorcycle on
a highway outside Rapid City, South Dakota, when a
truck driven by respondent Randy Shauers struck him
from behind. Warger claims he was stopped at the time of
the accident, while Shauers claims that Warger suddenly
pulled out in front of him. Regardless of the cause of the
accident, no one disputes its tragic result: Warger sus-
tained serious injuries that ultimately required the ampu-
tation of his left leg.
  Warger sued Shauers for negligence in Federal District
Court. During jury selection, counsel for both parties
2                  WARGER v. SHAUERS

                     Opinion of the Court

conducted lengthy voir dire of the prospective jurors.
Warger’s counsel asked whether any jurors would be
unable to award damages for pain and suffering or for
future medical expenses, or whether there was any juror
who thought, “I don’t think I could be a fair and impartial
juror on this kind of case.” App. 105. Prospective juror
Regina Whipple, who was later selected as the jury fore-
person, answered no to each of these questions. See 

89, 105.
  Trial commenced, and the jury ultimately returned a
verdict in favor of Shauers. Shortly thereafter, one of the
jurors contacted Warger’s counsel to express concern over
juror Whipple’s conduct. The complaining juror subse-
quently signed an affidavit claiming that Whipple had
spoken during deliberations about “a motor vehicle colli-
sion in which her daughter was at fault for the collision
and a man died,” and had “related that if her daughter
had been sued, it would have ruined her life.” App. to Pet.
for Cert. 40a–41a.
  Relying on this affidavit, Warger moved for a new trial.
He contended that Whipple had deliberately lied during
voir dire about her impartiality and ability to award dam-
ages. Thus, he asserted, he had satisfied the requirements
of McDonough Power Equipment, Inc. v. Greenwood, 

(1984), which holds that a party may “obtain a
new trial” if he “demonstrate[s] that a juror failed to an-
swer honestly a material question on voir dire, and . . .
that a correct response would have provided a valid basis
for a challenge for cause.” 

  The District Court refused to grant a new trial, holding
that the only evidence that supported Warger’s motion,
the complaining juror’s affidavit, was barred by Federal
Rule of Evidence 606(b). As relevant here, that Rule
provides that “[d]uring an inquiry into the validity of a
verdict,” evidence “about any statement made or incident
that occurred during the jury’s deliberations” is inadmis-
                 Cite as: 574 U. S. ____ (2014)           3

                     Opinion of the Court

sible. Rule 606(b)(1). The Rule contains three specific
exceptions—allowing testimony “about whether (A) extra-
neous prejudicial information was improperly brought to
the jury’s attention; (B) an outside influence was improp-
erly brought to bear on any juror; or (C) a mistake was
made in entering the verdict on the verdict form,” Rule
606(b)(2)—but the District Court found none of these
exceptions to be applicable.
   The Eighth Circuit affirmed. 

(2013). It
first held that Warger’s proffered evidence did not fall
within the “extraneous prejudicial evidence” exception set
forth in Rule 606(b)(2)(A). The court explained that
“[j]urors’ personal experiences do not constitute extrane-
ous information; it is unavoidable they will bring such
innate experiences into the jury room.” 

Next,
the court rejected Warger’s alternative argument that
Rule 606(b) is wholly inapplicable when a litigant offers
evidence to show that a juror was dishonest during voir
dire. Acknowledging that there was a split among the
Federal Courts of Appeals on this question, the Eighth
Circuit joined those Circuits that had held that Rule
606(b) applies to any proceeding in which the jury’s verdict
might be invalidated, including efforts to demonstrate that
a juror lied during voir dire. Compare 

(citing Williams v. Price, 

, 235–237 (CA3
2003), and United States v. Benally, 

, 1235
(CA10 2008)), with Hard v. Burlington N. R. Co., 

, 485 (CA9 1987) (“Statements which tend to show
deceit during voir dire are not barred by [Rule 606(b)]”),
and Maldonado v. Missouri P. R. Co., 

, 770
(CA5 1986) (same).
   We granted certiorari, 571 U. S. ___ (2014), and now
affirm.
                         II
  We hold that Rule 606(b) applies to juror testimony
4                   WARGER v. SHAUERS

                     Opinion of the Court

during a proceeding in which a party seeks to secure a
new trial on the ground that a juror lied during voir dire.
In doing so, we simply accord Rule 606(b)’s terms their
plain meaning. The Rule, after all, applies “[d]uring an
inquiry into the validity of a verdict.” Rule 606(b)(1). A
postverdict motion for a new trial on the ground of
voir dire dishonesty plainly entails “an inquiry into the
validity of [the] verdict”: If a juror was dishonest during
voir dire and an honest response would have provided a
valid basis to challenge that juror for cause, the verdict
must be invalidated. See 

.
    This understanding of the text of Rule 606(b) is con-
sistent with the underlying common-law rule on which it
was based. Although some common-law courts would
have permitted evidence of jury deliberations to be intro-
duced to demonstrate juror dishonesty during voir dire,
the majority would not, and the language of Rule 606(b)
reflects Congress’ enactment of the more restrictive ver-
sion of the common-law rule.
    Rule 606(b) had its genesis in Vaise v. Delaval, 1 T. R.
11, 99 Eng. Rep. 944 (K. B. 1785), in which Lord Mansfield
held inadmissible an affidavit from two jurors claiming
that the jury had decided the case through a game of
chance. See 8 J. Wigmore, Evidence §2352, p. 696 (J.
McNaughton rev. 1961). The rule soon took root in the
United States, 

where it was viewed as
both promoting the finality of verdicts and insulating the
jury from outside influences, see McDonald v. Pless, 

, 267–268 (1915).
    Some versions of the rule were narrower than others.
Under what was sometimes known as the “Iowa” ap-
proach, juror testimony regarding deliberations was ex-
cluded only to the extent that it related to matters that
“ ‘inhere[d] in the verdict,’ ” which generally consisted of
evidence of the jurors’ subjective intentions and thought
processes in reaching a verdict. 3 C. Mueller & L. Kirk-
                     Cite as: 574 U. S. ____ (2014)                     5

                          Opinion of the Court

patrick, Federal Evidence §6:16, p. 70 (4th ed. 2013); 8
Wigmore, Evidence §§2353, 2354, at 699–702.1 A number
of courts adhering to the Iowa rule held that testimony
regarding jury deliberations is admissible when used to
challenge juror conduct during voir dire. See, e.g., Mathi-
sen v. Norton, 

, 244–246, 

, 3–4
(1936); Williams v. Bridges, 

, 538–541,

, 408–409 (1934).
   But other courts applied a broader version of the anti-
impeachment rule. Under this version, sometimes called
the “federal” approach, litigants were prohibited from
using evidence of jury deliberations unless it was offered
to show that an “extraneous matter” had influenced the
jury. See 3 Mueller & Kirkpatrick, Federal Evidence
§6:16, at 71; Rules of Evidence for United States Courts
and Magistrates, 56 F. R. D. 183, 265 (1973). The “great
majority” of appellate courts applying this version of the
rule held jury deliberations evidence inadmissible even if
used to demonstrate dishonesty during voir dire. Wilson
v. Wiggins, 

, 246, 

, 872 (1939); see,
e.g., Willis v. Davis, 

, 314 (Okla. 1958);
Turner v. Hall’s Adm’x, 

, 34 (Ky. 1952);
Hinkel v. Oregon Chair Co., 80 Ore. 404, 406, 

,
439 (1916); State v. Cloud, 

, 958–960, 

, 828–829 (1912); Payne v. Burke, 

,
528–530, 260 N. Y. S. 259, 260–262 (1932).
   This Court occasionally employed language that might
——————
  1 The Iowa rule derived from Wright v. Illinois & Miss. Tel. Co., 

(1866), in which the Iowa Supreme Court held that a trial
court considering a motion for a new trial should have accepted the
affidavits of four jurors who claimed that their damages verdict had
been determined by taking the average of the sums each juror thought
proper (a “quotient” verdict). 

The Wright court rea-
soned that, unlike evidence of a juror’s subjective intentions in reaching
a verdict, whether the verdict had been obtained in this fashion was an
“independent fact” and thus could and should be proved by any avail-
able evidence. 

6                   WARGER v. SHAUERS

                     Opinion of the Court

have suggested a preference for the Iowa rule. See Hyde
v. United States, 

, 383–384 (1912) (“[W]e
think the rule expressed in Wright v. Illinois & Miss. Tel.
Co., 

[1866], . . . should apply, that the testi-
mony of jurors should not be received to show matters
which essentially inhere in the verdict itself and neces-
sarily depend upon the testimony of the jurors and can
receive no corroboration”); Mattox v. United States, 

, 148–149 (1892) (quoting at length a Kansas
Supreme Court decision setting out the Iowa test). But to
the extent that these decisions created any question as to
which approach this Court followed, McDonald v. Pless
largely settled matters. There, we held that juror affida-
vits were not admissible to show that jurors had entered a
“quotient” verdict, precisely the opposite of the result
reached by the Iowa Supreme Court in its decision estab-
lishing the Iowa approach. 

,
268, with Wright v. Illinois & Miss. Tel. Co., 

,
211–212 (1866). In doing so, we observed that although
decisions in a few States made admissible a “juror’s affi-
davit as to an overt act of misconduct, which was capable
of being controverted by other jurors,” the argument in
favor of that approach (i.e., the Iowa rule) had not been
generally accepted, because permitting such evidence
“would open the door to the most pernicious arts and
tampering with 

(internal quota-
tion marks omitted).
   Our subsequent decision in Clark v. United States, 

(1933), was consistent with our apparent rejection
of the Iowa approach. In Clark, the Government had
prosecuted for contempt a juror who, during voir dire in a
prior case, had falsely denied knowing the defendant. 

We held that the prosecution could introduce
evidence of what had occurred during deliberations in the
prior case, rejecting the juror’s argument that these com-
munications were privileged. We were careful to explain,
                    Cite as: 574 U. S. ____ (2014)                  7

                        Opinion of the Court

however, that nothing in our decision was “at variance
with the rule . . . that the testimony of a juror is not ad-
missible for the impeachment of his verdict.” 

This was because the verdict in the original case was not
at issue, and therefore “the rule against impeachment
[was] wholly unrelated to the problem . . . before us.”
Ibid.; accord, 

. Clark thus
clarified that the rule against jurors’ impeaching their
verdicts applies only in a proceeding actually impeaching
that verdict—precisely the line Rule 606(b) draws when it
refers to an “inquiry into the validity of a verdict.”
   In any event, these decisions predated Congress’ enact-
ment of Rule 606(b), and Congress was undoubtedly free
to prescribe a broader version of the anti-impeachment
rule than we had previously applied. The language of the
Rule it adopted clearly reflects the federal approach: As
enacted, Rule 606(b) prohibited the use of any evidence of
juror deliberations, subject only to the express exceptions
for extraneous information and outside influences.2
   For those who consider legislative history relevant, here
it confirms that this choice of language was no accident.
Congress rejected a prior version of the Rule that, in ac-
cordance with the Iowa approach, would have prohibited
juror testimony only as to the “effect of anything upon . . .
[any] juror’s mind or emotions . . . or concerning his men-
tal processes.” Committee on Rules of Practice and Proce-
dure of the Judicial Conference of the United States,
Revised Draft of Proposed Rules of Evidence for the United
States Courts and Magistrates, 51 F. R. D. 315, 387
(1971); see Tanner v. United States, 

, 123–
125 (1987) (detailing the legislative history of the Rule).
Thus Congress “specifically understood, considered, and
rejected a version of Rule 606(b)” that would have likely
——————
  2 The additional exception for mistakes made in entering the verdict

on the verdict form was adopted in 2006. See 

, 1286.
8                    WARGER v. SHAUERS

                      Opinion of the Court

permitted the introduction of evidence of deliberations to
show dishonesty during voir dire. 

                              III

                               A

   Seeking to rebut this straightforward understanding of
Rule 606(b), Warger first insists that the proceedings that
follow a motion for new trial based on dishonesty during
voir dire do not involve an “inquiry into the validity of the
verdict.” His argument is as follows: Under McDonough, a
party moving for a new trial on the basis of voir dire dis-
honesty need not show that this dishonesty had an effect
on the verdict. 

. Although a success-
ful claim will result in vacatur of the judgment, vacatur is
simply the remedy for the McDonough error, just as it may
be the remedy for a variety of errors that have nothing to
do with the manner in which the jury reached its verdict.
See, e.g., United States v. Davila, 569 U. S. ___, ___ (2013)
(slip op., at 12) (listing certain “ ‘structural’ ” errors war-
ranting “automatic reversal” of a criminal conviction).
Therefore, Warger asserts, the “inquiry begins and ends
with what happened during voir dire.” Brief for Petitioner
19–20.
   We are not persuaded. Warger, it seems, would restrict
Rule 606(b)’s application to those claims of error for which
a court must examine the manner in which the jury
reached its verdict—claims, one might say, involving an
inquiry into the jury’s verdict. But the “inquiry” to which
the Rule refers is one into the “validity of the verdict,” not
into the verdict itself. The Rule does not focus on the
means by which deliberations evidence might be used to
invalidate a verdict. It does not say “during an inquiry
into jury deliberations,” or prohibit the introduction of
evidence of deliberations “for use in determining whether
an asserted error affected the jury’s verdict.” It simply
applies “[d]uring an inquiry into the validity of the ver-
                  Cite as: 574 U. S. ____ (2014)            9

                      Opinion of the Court

dict”—that is, during a proceeding in which the verdict
may be rendered invalid. Whether or not a juror’s alleged
misconduct during voir dire had a direct effect on the
jury’s verdict, the motion for a new trial requires a court to
determine whether the verdict can stand.
                             B
   Next, Warger contends that excluding jury deliberations
evidence tending to show that a juror lied during voir dire
is unnecessary to fulfill Congress’ apparent objectives of
encouraging full and open debate in the jury room and
preventing the harassment of former jurors. He observes
that jurors remain free to, and may sometimes be forced
to, disclose what happened in the jury room, and that
ethical rules limit the ability of parties to harass jurors
following trial. But these are arguments against Rule
606(b) generally, not arguments for the particular excep-
tion to the Rule that Warger seeks. Congress’ enactment
of Rule 606(b) was premised on the concerns that the use
of deliberations evidence to challenge verdicts would
represent a threat to both jurors and finality in those
circumstances not covered by the Rule’s express excep-
tions. Warger cannot escape the scope of the Rule Con-
gress adopted simply by asserting that its concerns were
misplaced.
                             C
  Nor do we accept Warger’s contention that we must
adopt his interpretation of Rule 606(b) so as to avoid
constitutional concerns. The Constitution guarantees both
criminal and civil litigants a right to an impartial jury.
See, e.g., Sheppard v. Maxwell, 

, 362 (1966);
Thiel v. Southern Pacific Co., 

, 220 (1946).
And we have made clear that voir dire can be an essential
means of protecting this right. See, e.g., Turner v. Mur-
ray, 

, 36 (1986) (plurality opinion); Ham v.
10                      WARGER v. SHAUERS

                          Opinion of the Court

South Carolina, 

, 527 (1973). These princi-
ples, Warger asserts, require that parties be allowed to
use evidence of deliberations to demonstrate that a juror
lied during voir dire.
   Given the clarity of both the text and history of Rule
606(b), however, the canon of constitutional avoidance has
no role to play here. The canon “is a tool for choosing
between competing plausible interpretations” of a provi-
sion. Clark v. Suarez-Martinez, 

, 381 (2005).
It “has no application in the absence of . . . ambiguity.”
United States v. Oakland Cannabis Buyers’ Cooperative,

, 494 (2001). We see none here.
   Moreover, any claim that Rule 606(b) is unconstitutional
in circumstances such as these is foreclosed by our deci-
sion in Tanner. In Tanner, we concluded that Rule 606(b)
precluded a criminal defendant from introducing evidence
that multiple jurors had been intoxicated during trial,
rejecting the contention that this exclusion violated the
defendant’s Sixth Amendment right to “ ‘a tribunal both
impartial and mentally competent to afford a hearing.’ 

(quoting Jordan v. Massachusetts, 

, 176 (1912)). We reasoned that the defendant’s
right to an unimpaired jury was sufficiently protected by
voir dire, the observations of court and counsel during
trial, and the potential use of “nonjuror evidence” of mis-

. Similarly here, a party’s right
to an impartial jury remains protected despite Rule
606(b)’s removal of one means of ensuring that jurors are
unbiased. Even if jurors lie in voir dire in a way that
conceals bias, juror impartiality is adequately assured
by the parties’ ability to bring to the court’s attention
any evidence of bias before the verdict is rendered, and
to employ nonjuror evidence even after the verdict is
rendered.3
——————
 3 There   may be cases of juror bias so extreme that, almost by defini-
                    Cite as: 574 U. S. ____ (2014) 
                11

                         Opinion of the Court 


                             IV 

   We further hold, consonant with the Eighth Circuit,
that the affidavit Warger sought to introduce was not
admissible under Rule 606(b)(2)(A)’s exception for evi-
dence as to whether “extraneous prejudicial information
was improperly brought to the jury’s attention.”
   Generally speaking, information is deemed “extraneous”
if it derives from a source “external” to the jury. See

. “External” matters include
publicity and information related specifically to the case
the jurors are meant to decide, while “internal” matters
include the general body of experiences that jurors are
understood to bring with them to the jury room. See 

27 C. Wright & V. Gold, Federal Practice and
Procedure: Evidence §6075, pp. 520–521 (2d ed. 2007).
Here, the excluded affidavit falls on the “internal” side of
the line: Whipple’s daughter’s accident may well have
informed her general views about negligence liability for
car crashes, but it did not provide either her or the rest of
the jury with any specific knowledge regarding Shauers’
collision with Warger.
   Indeed, Warger does not argue that Whipple’s state-
ments related to “extraneous” information in this sense.
Instead, he contends that because Whipple would have
been disqualified from the jury had she disclosed her
daughter’s accident, any information she shared with the
other jurors was extraneous.
   We cannot agree that whenever a juror should have
been excluded from the jury, anything that juror says is
necessarily “extraneous” within the meaning of Rule
606(b)(2)(A). Were that correct, parties would find it quite
——————
tion, the jury trial right has been abridged. If and when such a case
arises, the Court can consider whether the usual safeguards are or are
not sufficient to protect the integrity of the process. We need not
consider the question, however, for those facts are not presented here.
12                  WARGER v. SHAUERS

                      Opinion of the Court

easy to avoid Rule 606(b)’s limitations. As discussed
above, Congress adopted the restrictive version of the anti-
impeachment rule, one that common-law courts had con-
cluded precludes parties from using deliberations evidence
to prove juror dishonesty during voir dire. But if Warger’s
understanding of the “extraneous” information exception
were accepted, then any time a party could use such evi-
dence to show that a juror’s “correct response [during
voir dire] would have provided a valid basis for a chal-
lenge”—a prerequisite for relief under 

—all evidence of what that juror said during
deliberations would be admissible. The “extraneous”
information exception would swallow much of the rest of
Rule 606(b).
   Even if such a result were not precluded by Congress’
apparent intent to adopt the restrictive federal approach,
it is foreclosed by Tanner, which relied upon the doctrine
that “treat[s] allegations of the physical or mental incom-
petence of a juror as ‘internal’ rather than ‘external’ mat-

. Tanner cited, in particular, cases
holding that evidence of jurors’ insanity, inability to un-
derstand English, and hearing impairments are all “inter-
nal” matters subject to exclusion under Rule 606(b). 

Were we to follow Warger’s understanding of the
“extraneous information” exception, all these cases, includ-
ing Tanner, would have been wrongly decided: If the ju-
rors were not able to serve on the jury in the first place, or
should have been dismissed for their misconduct during
the trial, then what they said or did during deliberations
would necessarily be “extraneous” and admissible. Tan-
ner’s implicit rejection of this view easily extends from the
sort of juror incompetence considered in that case to the
alleged bias considered here. Whether a juror would have
been struck from the jury because of incompetence or bias,
the mere fact that a juror would have been struck does not
make admissible evidence regarding that juror’s conduct
                 Cite as: 574 U. S. ____ (2014)                 13

                     Opinion of the Court

and statements during deliberations.

  For the foregoing reasons, the judgment of the United
States Court of Appeals for the Eighth Circuit is affirmed.

                                                  It is so ordered.