Background
Plaintiff Gretchen Getter brought this diversity action alleging that she sustained personal injuries due to the negligence of defendant Wal-Mart Stores, Inc. Plaintiff alleges that she was injured when she slipped and fell in the vestibule of defendant’s store in Atchison, Kansas on December 20,1989. After a three-day trial, the jury returned a verdict for defendant. Plaintiff then moved for a new trial, and the district court denied the motion. Plaintiff now appeals to this court. We exercise jurisdiction pursuant to 28 U.S.C. § 1291 and affirm.
Plaintiff contends that she is entitled to a new trial because the district court erred by (1) denying plaintiffs for-cause challenge to prospective juror John Agin, (2) excluding plaintiffs expert witness Keith Vidal, (3) admitting the lay opinion testimony of Emma Jean Bramble and Cynthia Gee, (4) allowing defendant to inquire into whether plaintiff had taken measures to prevent pregnancy, and (5) submitting Jury Instruction No. 11. Plaintiff also alleges that the cumulative effect of these errors unfairly prejudiced her *1122and that the jury’s verdict was against the weight of the evidence.
Denial of For-Cause Challenge to Prospective Juror
“We review the district court’s refusal to strike a juror for cause for an abuse of discretion, keeping in mind that ‘the district court is in the best position to observe the juror and to make a first-hand evaluation of his ability to be fair.’” Vasey v. Martin Marietta Corp., 29 F.3d 1460, 1467 (10th Cir.1994) (citation omitted) (quoting Wilson v. Johns[on]-Manville Sales Corp., 810 F.2d 1358, 1361 (5th Cir.), cert. denied, 484 U.S. 828,108 S.Ct. 97, 98 L.Ed.2d 58 (1987)). The district court must grant a challenge for cause, however, if a prospective juror shows actual prejudice or bias. Id. Actual bias can be shown either by the juror’s own admission of bias or “by proof of specific facts which show the juror has such a close connection to the facts at trial that bias is presumed.” Id.
In our recent Vasey decision, we noted that “courts have presumed bias in extraordinary situations where a prospective juror has had a direct financial interest in the trial’s outcome.” Id. at 1468. As examples of such extraordinary situations, we cited a case in which a prospective juror was a stockholder in or an employee of a corporation that was a party to the suit. Id. (citing Gladhill v. General Motors Corp., 743 F.2d 1049 (4th Cir.1984); Francone v. Southern Pac. Co., 145 F.2d 732 (5th Cir.1944)). “In these situations, the relationship between the prospective juror and a party to the lawsuit ‘point[s] so sharply to bias in [the] particular juror’ that even the juror’s own assertions of impartiality must be discounted in ruling on a challenge for cause.” Id. (quoting United States v. Nell, 526 F.2d 1223, 1229 n. 8 (5th Cir.1976)).
The challenged prospective juror in this case, John Agin, disclosed during voir dire that he owned stock in defendant corporation and that his wife was then employed by defendant. The district court questioned Mr. Agin regarding his ability to be a fair and impartial juror in light of his connections to defendant. Mr. Agin responded that he had no doubt that he could be fair and impartial. When later questioned by plaintiffs counsel, Mr. Agin assured counsel that he could support a verdict against defendant if the evidence presented at trial warranted such a result. Nevertheless, when the district court refused to dismiss Mr. Agin for cause, plaintiff used a peremptory challenge to remove him from the jury.
Despite Mr. Agin’s assurances of his impartiality, the district court abused its discretion by denying plaintiffs challenge for cause. Due to his stock ownership and his wife’s employment, Mr. Agin’s financial well-being was to some extent dependent upon defendant’s. This is precisely the type of relationship that requires the district court to presume bias and dismiss the prospective juror for cause. See Vasey, 29 F.3d at 1460; Gladhill, 743 F.2d at 1050 (“ ‘That a stockholder in a company which is [a] party to a lawsuit is incompetent to sit as a juror is so well settled as to be black letter law.’ ”) (quoting Chestnut v. Ford Motor Co., 445 F.2d 967, 971 (4th Cir.1971)).
Having concluded that the district court erred by refusing to grant plaintiffs for-eause challenge to prospective juror Agin, we next must determine whether this error warrants reversal. Plaintiff argues that an erroneous denial of a challenge for cause is reversible error because it forces the litigant to exercise a peremptory challenge. We note that some circuits consider the loss of a peremptory challenge per se reversible error. See, e.g., United States v. Cambara, 902 F.2d 144, 147 (1st Cir.1990) (stating that “restricting a defendant’s use of the lawful number of peremptory challenges is reversible error if a challenge for cause is erroneously denied”); United States v. Ruuska, 883 F.2d 262, 268 (3d Cir.1989) (“[T]he denial or impairment of the right to peremptory challenges is reversible error per se.... [It] cannot be dismissed as harmless.”) (citations omitted). In our view, however, recent Supreme Court decisions compel the application of harmless error analysis. See Ross v. Oklahoma, 487 U.S. 81, 88, 108 S.Ct. 2273, 2278, 101 L.Ed.2d 80 (1988); McDonough Power Equip., Inc. v. Greenwood, 464 U.S. 548, 553, 104 S.Ct. 845, 848, 78 L.Ed.2d 663 (1984). (“[C]ourts should ... ignore errors *1123that do not affect the essential fairness of the trial.”).
In Boss, a state court capital punishment case, the trial court erroneously refused to dismiss a juror for cause. As a result, the defendant was forced to use a peremptory challenge to remove the juror. Stating that it had “long recognized that peremptory challenges are not of constitutional dimension,” the Court rejected “the notion that the loss of a peremptory challenge constitutes a violation of the constitutional right to an impartial jury.” Ross, 487 U.S. at 88, 108 S.Ct. at 2278. Thus, “[s]o long as the jury that sits is impartial, the fact that the defendant had to use a peremptory challenge to achieve that result does not mean the Sixth Amendment was violated.” Id.1
The Ross Court next examined whether the defendant’s right to due process was violated by the juror selection process. Under state law, the defendant was required to use a peremptory challenge to cure the trial court’s erroneous refusal to excuse a juror for cause in order to preserve the issue for appeal. Id. at 89, 108 S.Ct. at 2278-79. Noting that “peremptory challenges are a creature of statute and are not required by the Constitution,” id., the Court held that because the defendant “received all that [state] law allowed him, ... his due process challenge fail[ed],” id. at 91, 108 S.Ct. at 2279-80.
In the instant case, plaintiff received all the peremptory challenges allowed by statute. See 28 U.S.C. § 1870. Thus, applying Ross, plaintiffs right to due process was not violated. Because the district court’s erroneous denial of plaintiffs for-cause challenge did not violate the Fifth Amendment or the Seventh Amendment, we must examine whether the district court’s erroneous denial of plaintiffs for-cause juror challenge—regardless of its effect on plaintiffs peremptory challenges—was harmless error.
Because the error here is nonconstitutional, we determine whether it was harmless using the standard established in Kotteakos v. United States, 328 U.S. 750, 66 S.Ct. 1239, 90 L.Ed. 1557 (1946). United States v. Rivera, 900 F.2d 1462, 1469 (10th Cir.1990).2 “A non-constitutional error is harmless unless it had a ‘substantial influence’ on the outcome [of the trial] or leaves one in ‘grave doubt’ as to whether it had such effect.” Id. at 1469 (quoting Kotteakos, 328 U.S. at 765, 66 S.Ct. at 1248.
In this case, the challenged juror did not serve on the jury because plaintiff used a peremptory challenge to remove him. Plaintiff does not allege that the jury as seated was biased. Thus, the district court’s refusal to remove Mr. Agin for cause did not have a “substantial influence on the outcome” of the trial, nor does it leave us “in grave doubt as to whether it had such effect.” Because plaintiffs right to an impartial jury was not infringed by the district court’s erroneous denial of the for-cause challenge, we hold that the error was harmless.3 See McIntyre, 997 F.2d at 698 n. 7.
*1124 District Court’s Evidentiary Decisions
Plaintiffs second, third, and fourth allegations of error question the trial court’s rulings on the admissibility of certain evidence. In general, a district court’s rulings on the admissibility of evidence will not be disturbed on appeal absent an abuse of discretion. Ragland v. Shattuck Nat’l Bank, 36 F.3d 983, 990 (10th Cir.1994).
Plaintiff first challenges the district court’s refusal to allow plaintiffs safety expert to testify. A district court may allow expert testimony “[i]f [the expert’s] scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue.” Fed.R.Evid. 702. “[A] trial judge’s ruling on the admission or exclusion of expert testimony will not be overturned unless it is manifestly erroneous or an abuse of discretion.” Werth v. Makita Elec. Works, Ltd., 950 F.2d 643, 647 (10th Cir.1991). Here, the district court excluded plaintiffs proffered expert testimony because “the normal life experiences and qualifications of the jury would permit it to draw its own conclusions concerning the safety of the floor, based upon the lay testimony of eyewitnesses.” This ruling was neither manifestly erroneous nor an abuse of discretion.
Plaintiff also argues that defense witnesses Bramble and Gee should not have been permitted to offer their opinions that the vestibule was safe at the time of plaintiffs fall. Each of these witnesses related her eyewitness observations concerning the vestibule’s condition. Each witness also opined that the vestibule was safe at the time that plaintiff slipped and fell. The Federal Rules of Evidence provide that a lay witness may testify in the form of an opinion if the opinion is “(a) rationally based on the perception of the witness and (b) helpful to a clear understanding of the witness’ testimony or the determination of a fact in issue.” Fed. R.Evid. 701. The determination of a lay witness’s qualification to testify to a matter of opinion is within the sound discretion of the trial court. Randolph v. Collectramatic, Inc., 590 F.2d 844, 847 (10th Cir.1979). In this case, the testimony of each challenged witness meets the requirements of Rule 701. Accordingly, the district court did not abuse its discretion in allowing Bramble and Gee to offer their opinions.
Plaintiffs remaining evidentiary claim is that the district court erred in permitting defendant to inquire, on cross examination, whether plaintiff had undergone a sterilization procedure to prevent pregnancy. Plaintiff argues that the inquiry was improper because its probative value was substantially outweighed by the danger of unfair prejudice to plaintiff. See Fed.R.Evid. 403. “The decision to exclude (or admit) evidence under [Rule 403] is within the sound discretion of the trial court, and will not be reversed by this court absent a clear abuse of discretion.” K-B Trucking Co. v. Riss Int’l Corp., 763 F.2d 1148, 1155 (10th Cir.1985). When plaintiff objected to this line of questioning at trial, the district court asked both counsel to approach the bench. Defendant argued that the question was relevant because plaintiffs complaint included a claim for lost consortium. While the district court allowed plaintiff to answer the question, the court also admonished defendant not to dwell on the subject. We cannot say that the district court clearly abused its discretion by allowing this evidence.
Jury Instructions
Plaintiff asserts that Jury Instruction No. 11 was improper because it was duplicative, vague, and confusing to the jury.4 *1125When reviewing a challenge to jury instructions, we must look at the instructions as a whole to determine whether they properly state the law. Lutz v. Weld County Sch. Dist. No. 6, 784 F.2d 340, 341 (10th Cir.1986) (per curiam). An instruction need not be faultless in every respect. Id. The judgment should be disturbed only if we have “a substantial doubt whether the jury was fairly guided in its deliberations.” Id. (internal quotations omitted). Upon review of the jury instructions as a whole, we conclude that they properly stated the law and fairly guided the jury in its deliberations.
Cumulative Error and Sufficiency of Evidence
Because we find that only one of the district court’s rulings challenged by plaintiff was error, and that the sole error was harmless, plaintiffs allegation of cumulative error fails. “[C]umuIative-error analysis should evaluate only the effect of matters determined to be error, not the cumulative effect of non-errors.” Rivera, 900 F.2d at 1471.
Plaintiffs final argument is that the jury verdict is against the weight of the evidence. “A motion for a new trial made on the ground that the verdict of the jury is against the weight of the evidence normally presents a question of fact and not of law and is addressed to the discretion of the trial court.” Richardson v. City of Albuquerque, 857 F.2d 727, 730 (10th Cir.1988). Thus, we review the district court’s denial of a motion for new trial on this ground for “a manifest abuse of discretion.” Id. Our “inquiry focuses on whether the verdict is clearly, decidedly or overwhelmingly against the weight of the evidence. Black v. Hieb's Enters., Inc., 805 F.2d 360, 363 (10th Cir.1986). In the case at bar, our review of the trial record reveals substantial evidence to support the jury’s verdict. Thus, the verdict is not clearly, decidedly, or overwhelmingly against the evidence. We therefore find no abuse of discretion in the district court’s denial of plaintiffs motion for a new trial.
Conclusion
For the reasons stated herein, the judgment of the district court is AFFIRMED.
. We recognize that Ross was concerned with the Sixth Amendment, not the Seventh Amendment, right to trial by jury. In our view, however, the rationale of Ross applies by analogy to the instant case. Moreover, there is no reason to believe that the Seventh Amendment would provide a broader right than the Sixth Amendment in this context. Cf. Colgrove v. Battin, 413 U.S. 149, 158-60, 93 S.Ct. 2448, 2453-54, 37 L.Ed.2d 522 (1973) (relying on a Sixth Amendment case to sustain the constitutionality of six-member juries in civil trials).
. This court recently reiterated the appropriateness of the Kotteakos standard in United States v. McIntyre, 997 F.2d 687, 698 n. 7 (10th Cir.1993) ("Because the erroneous denial of a for-cause challenge does not rise to the level of a constitutional violation, we apply the harmless error analysis set forth in Kotteakos."), cert. denied,U.S.-, 114 S.Ct. 736, 126 L.Ed.2d 699 (1994).
. We are troubled that one result of our holding may be the creation of a formidable barrier to appellate review of denials of for-cause challenges. Unless a litigant's right to an impartial jury is infringed, erroneous denials of for-cause challenges are probably harmless errors. A litigant who challenges a prospective juror for cause is unlikely to allow such a juror to remain on the jury and will exercise a peremptory challenge. Thus, the litigant will not be able to argue that the jury which decided the case was partial. Of course, there may be instances in which a party can show that the erroneous denial of a for-cause challenge substantially affected the outcome of a trial. Such an instance, however, is not before us in this case.
. The challenged jury instruction is set forth here in full:
This instruction sets forth the claims of the respective parties, as stated in the case. These claims are not to be considered by you as evidence in the case. The allegations of the respective parties must be established and proved by the evidence.
In this case plaintiff, Gretchen Getter, claims that she was injured and sustained damages as a result of the fault of defendant Wal-Mart Stores, Inc., in one or more of the following respects:
(1) Defendant failed to have mats covering a wet floor in the vestibule of the store;
(2) Defendant failed to replace wet mats in the vestibule in a timely manner;
(3) Defendant failed to eliminate the dangerous condition of wet floors in a timely manner.
*1125The plaintiff bears the burden of proving that her claims are more probably true than not true.
The defendant admits that it operated the Wal-Mart Store in Atchison County, Kansas, and that the store had a vestibule on December 20, 1988, for customers to enter and exit. Wal-Mart also admits that Gretchen Getter was a business visitor in its store at the time of the occurrence in question.
The defendant denies all other claims of plaintiff.
Further, defendant claims that if the plaintiff sustained injury or damages, it was the fault of plaintiff in one or more of the following respects:
(1) In failing to keep a proper lookout for her own safety;
(2) In failing to look and see what was in plain sight, there being nothing to prevent plaintiff from seeing the floor;
(3) In the manner in which she walked through the vestibule area in view of the inclement weather conditions.
The defendant has the burden of proving that its claims of fault on the part of plaintiff are more probably true than not true.
Plaintiff challenges only the emphasized portion of the instruction.