Presentation of evidence - Bias and interest

Learning Outcomes

This article explains how bias and interest operate as methods of impeaching witnesses on the MBE, including:

• Recognizing fact patterns that raise bias or interest issues and distinguishing them from mere attacks on general credibility.
• Distinguishing bias and interest from other impeachment methods such as character for untruthfulness, prior convictions, prior inconsistent statements, or contradiction.
• Applying the Federal Rules of Evidence that govern cross-examination and extrinsic evidence when proving bias or interest, including when extrinsic proof is mandatory, optional, or barred.
• Evaluating when trial courts may limit, exclude, or permit bias and interest evidence under Rule 403, Rule 610, constitutional confrontation principles, and judge-controlled mode-and-order rules.
• Determining the proper sequence for confronting a witness with alleged bias, laying a preliminary foundation, and then offering extrinsic evidence if the witness denies or minimizes the relationship or motive.
• Analyzing how hearsay, character, and collateral-matter doctrines interact with bias and interest impeachment, particularly when documents or third-party witnesses are used to prove motive.
• Selecting the best MBE answer choice by prioritizing strong bias or interest evidence over weaker impeachment options and spotting when additional proof would be cumulative or improper.

MBE Syllabus

For the MBE, you are required to understand how bias and interest affect the credibility of witnesses and the presentation of evidence, with a focus on the following syllabus points:

• Impeachment of witnesses by showing bias or interest.
• Use of cross-examination and extrinsic evidence to prove bias or interest.
• Procedural requirements for making the necessary preliminary showing and preserving issues for appeal.
• Interaction of bias and interest evidence with other Federal Rules of Evidence (e.g., Rules 403, 404, 608, 609, 610).
• Limits on admissibility and the judge’s discretion to control the mode and order of proof.

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. Which of the following is a proper method for impeaching a witness based on bias?
   1. Asking about prior convictions only
   2. Cross-examining about the witness’s relationship to a party
   3. Introducing evidence of prior inconsistent statements only
   4. Asking about the witness’s religious beliefs
2. When may extrinsic evidence of a witness’s bias be introduced?
   1. Only after the witness denies bias on cross-examination
   2. Only if the witness is a party
   3. Always, subject to relevance and procedural rules
   4. Never
3. Which of the following best describes "interest" as a ground for impeachment?
   1. The witness’s criminal record
   2. The witness’s motive to lie due to a personal stake in the outcome
   3. The witness’s prior inconsistent statements
   4. The witness’s lack of memory
4. If a witness admits bias on cross-examination, may further extrinsic evidence be introduced to prove the same bias?
   1. Yes, always
   2. No, unless the court allows it for good cause
   3. No, unless the witness denies or fails to admit the bias
   4. Yes, but only if the witness is a party

Introduction

Bias and interest are central grounds for attacking a witness’s credibility. The Federal Rules of Evidence and modern common law treat a witness’s partiality or personal stake in the outcome as powerful reasons to doubt that witness’s testimony. Unlike some other forms of impeachment, bias and interest are almost never considered “collateral”; they go directly to whether the fact-finder should trust what the witness says.

Key Term: Impeachment
Challenging a witness’s credibility by showing reasons the fact-finder should not fully believe or rely on the witness’s testimony.

Bias and Interest: Definitions and Relevance

Key Term: Bias
A tendency, motive, or relationship that may cause a witness to favor or disfavor a party, affecting how the witness perceives, remembers, or recounts events.

Key Term: Interest
A witness’s direct personal stake in the outcome of the case—often financial, legal, or otherwise tangible—that may give the witness a motive to lie or shade testimony.

Bias includes many forms of partiality, such as:

• Family or close personal relationship with a party.
• Hostility or prior disputes with a party.
• Employment, business, or financial relationship with a party.
• Sympathy, loyalty, or ideological alignment.

Interest is technically one type of bias, but MBE questions sometimes distinguish them: “interest” is usually a concrete stake in the outcome (e.g., potential civil liability, share of a recovery), whereas “bias” can be broader (e.g., friendship or hatred without direct monetary stake).

Bias and interest are always relevant to credibility. Under Rule 401, any evidence that makes it more or less probable that a witness has a motive to testify in a particular way is relevant. Because bias goes to credibility rather than to propensity, it is not barred by Rule 404’s character limitations and is not restricted by Rule 608(b)’s prohibition on extrinsic evidence of specific acts when offered solely to show character for untruthfulness.

Why Bias Matters More Than General Character

Evidence that a witness is “the sort of person who lies” (character for untruthfulness) is probative, but relatively weak. Evidence that this particular witness has a concrete reason to want the defendant acquitted or the plaintiff to win is usually more compelling.

• A witness with no record but a strong financial stake may be highly suspect.
• A witness with a record but no apparent bias may still be reasonably credible on the specific events.

MBE questions often give you multiple possible impeachment methods. When bias or interest is clearly present, that is usually the most powerful (and thus best) answer choice.

Methods of Proving Bias and Interest

Bias or interest may be shown by two main methods:

• Cross-examining the witness about facts showing bias or interest.
• Introducing extrinsic evidence (documents, other witnesses) to prove those facts if the witness denies, minimizes, or fails to admit them.

Key Term: Extrinsic Evidence
Evidence from outside the witness’s own in-court testimony—such as documents, recordings, or testimony from other witnesses—offered to prove bias, interest, or other facts.

Cross-Examination to Show Bias or Interest

Rule 611(b) provides that cross-examination may cover matters addressed on direct and matters affecting the witness’s credibility. Because bias and interest directly affect credibility, a cross-examiner may always inquire into bias, even if it was not touched on during direct examination.

Typical cross-examination questions to show bias or interest include:

• “You are the plaintiff’s sister, correct?”
• “You are employed by the defendant’s company?”
• “You are currently on probation, and the prosecutor has some control over whether you are violated?”
• “You have a pending civil suit against the defendant arising out of this same incident?”

Counsel must have a good-faith basis for the question. If the witness denies the suggested bias, counsel should be prepared to prove it with extrinsic evidence.

Extrinsic Evidence of Bias or Interest

Unlike some other impeachment methods, extrinsic evidence to prove bias or interest is generally allowed, subject to ordinary relevance and Rule 403 balancing. Courts treat bias as noncollateral.

Key Term: Collateral Matter
A fact relevant only to impeaching a witness on a tangential point, not to any substantive issue or to major credibility concerns; extrinsic evidence is usually barred to prove such matters.

Bias and interest are not “collateral” in this sense, so documents and other witnesses may be used to prove them. Examples of admissible extrinsic evidence include:

• A copy of a will showing the witness as a beneficiary.
• A written plea agreement giving a witness favorable treatment for cooperating.
• Employment records showing the witness works for a party.
• A copy of a civil complaint the witness has filed against a party.

Importantly, Rule 608(b) bars extrinsic evidence of specific instances of conduct when offered solely to show a witness’s character for untruthfulness. But if the same conduct is offered to prove bias or interest, the bar does not apply. For example, extrinsic proof that a witness was fired by the defendant is permissible to show hostility, even though that firing might also suggest the witness bears a grudge.

Key Term: Preliminary Showing
The preliminary questioning or evidence needed to justify admission of further evidence, such as confronting a witness with alleged facts showing bias before introducing extrinsic proof.

Procedural Requirements

Most courts follow this sequence for bias or interest impeachment:

• First, confront the witness on cross-examination with the facts suggesting bias or interest.
• If the witness clearly admits the bias, the judge has discretion to limit additional extrinsic proof as cumulative.
• If the witness denies, minimizes, or equivocates, extrinsic evidence may be introduced.

If the court excludes extrinsic evidence, counsel must have made a proper offer of proof to preserve the issue for appeal.

The timing and manner are within the trial judge’s broad discretion under Rules 611(a) and 403. Judges may exclude bias evidence if:

• It risks unfair prejudice that substantially outweighs its probative value.
• It would confuse the issues or mislead the jury.
• It would cause undue delay or waste of time (e.g., mini-trial on a remote dispute).

However, especially in criminal cases, the defendant’s constitutional right to confront adverse witnesses limits how far a judge may go in excluding significant bias evidence. A court that completely prevents the defense from exposing an important government witness’s motive to testify favorably for the state risks reversible error.

Limits on Admissibility

Even though bias and interest are always relevant, they remain subject to exclusion under Rule 403 and some specific rules.

• Rule 403 balancing: Evidence may be excluded if its probative value is substantially outweighed by dangers such as unfair prejudice, confusion, or cumulative presentation. For example:

  • Showing that a witness once had a minor disagreement with a party decades ago may be so remote that its probative value is slight.
  • Proving bias through highly inflammatory extrinsic acts unrelated to the case might be excluded as unfairly prejudicial.

• Rule 610 (religious beliefs): Evidence of a witness’s religious beliefs or opinions is not admissible to attack or support credibility. However, courts may admit religious affiliation if it is specifically relevant to bias (e.g., both the witness and party belong to a small religious group whose members routinely favor each other). MBE questions often test this distinction by treating unexplained inquiries into “religious beliefs” as improper impeachment.

• Hearsay: Bias or interest evidence is often based on out-of-court statements (e.g., a plea agreement, a demand letter). When such statements are offered not for their truth but to show the existence of a relationship, promise, or motive, they are nonhearsay. The hearsay rule does not bar them.

Distinction from Other Impeachment Methods

Bias and interest differ from other impeachment categories:

• Character for untruthfulness (Rule 608(a), 609):
  Focuses on the witness’s general propensity to lie, proved by reputation/opinion or certain criminal convictions. Bias and interest focus instead on a particular motive to lie in this case.

• Specific acts of dishonesty (Rule 608(b)):
  Allow cross-examination about specific dishonest acts (e.g., lying on a job application) but bar extrinsic proof. By contrast, similar acts can be proved extrinsically when relevant to bias (e.g., the fact that the witness was fired by this defendant, showing hostility).

• Prior inconsistent statements (Rule 613):
  Attack the reliability of testimony by showing the witness said something different before. That is about inconsistency, not motive.

• Contradiction:
  Uses other evidence to contradict a witness’s testimony about specific facts. Contradiction focuses on accuracy; bias focuses on motive.

Because bias and interest speak directly to why a witness might slant testimony, they are often considered one of the strongest forms of impeachment. On the MBE, when multiple impeachment routes are available, evidence of bias or interest is frequently the best answer.

Worked Example 1.1

A witness testifies for the plaintiff in a personal injury case. On cross-examination, the defense asks if the witness is the plaintiff’s cousin and stands to inherit money if the plaintiff wins. The witness denies any financial interest. May the defense introduce a copy of the plaintiff’s will showing the witness as a beneficiary?

Answer:
Yes. Since the witness denied having a financial interest, the defense may introduce extrinsic evidence (the will) to prove the witness’s interest in the outcome. Bias and interest are not collateral, so extrinsic evidence is allowed, subject to Rule 403.

Worked Example 1.2

A police officer testifies for the prosecution. The defense asks if the officer is facing disciplinary charges that the prosecutor has promised to help resolve in exchange for testimony. The officer admits this on cross-examination. May the defense call another witness to testify about the deal?

Answer:
Generally, no. Once the officer has clearly admitted the existence and terms of the deal, further extrinsic evidence would be cumulative. The court may exclude additional proof as a waste of time under Rule 403.

Worked Example 1.3

In a robbery trial, the prosecution’s main witness is a co-defendant who entered into a plea agreement. On cross-examination, the defense asks, “You’re hoping for a lighter sentence because of your testimony today, correct?” The witness denies any such hope. The defense seeks to introduce the written plea agreement, which states that the prosecution will recommend a reduced sentence if the witness testifies truthfully at trial. Is the agreement admissible?

Answer:
Yes. The witness has denied the very bias the defense seeks to show. The plea agreement is extrinsic evidence directly proving the witness’s interest in testifying favorably for the prosecution. It is admissible to show bias, subject to Rule 403 balancing.

Worked Example 1.4

In a civil fraud case, the defendant calls a neighbor as a character witness to testify that the defendant has a reputation for honesty. On cross-examination, the plaintiff wants to show that the neighbor is a long-time business partner of the defendant and shares in the profits of the defendant’s business. The neighbor admits that they are friends but denies any financial relationship. May the plaintiff call an accountant to testify that the neighbor owns a 30% interest in the defendant’s business?

Answer:
Yes. The accountant’s testimony is extrinsic evidence of the neighbor’s financial interest in the defendant’s business, and thus in the outcome of the case. This is classic bias evidence, not barred as collateral, and can be proved extrinsically.

Exam Warning

Evidence of bias or interest is always relevant, but courts may limit repetitive or cumulative evidence. Once a witness clearly admits key facts showing bias, additional documents or witnesses on the same point are likely to be excluded. In an MBE question, if you see a clear admission, do not assume further extrinsic evidence is automatically admissible.

Revision Tip

When analyzing an MBE fact pattern involving impeachment, ask: “Does this witness have a reason to favor or disfavor a party or to gain personally from the outcome?” If yes, think bias or interest first, then decide whether cross-examination alone is enough or whether extrinsic evidence is permitted and useful.

Key Point Checklist

This article has covered the following key knowledge points:

• Bias is any relationship, motive, or predisposition to favor or disfavor a party; interest is a direct personal stake in the outcome.
• Bias and interest are always relevant to credibility and are among the most powerful forms of impeachment.
• Bias or interest may be proved through cross-examination and, if denied or minimized, by extrinsic evidence.
• Bias and interest are not collateral matters; extrinsic evidence is generally admissible, subject to Rule 403.
• Rule 608(b)’s limit on extrinsic evidence of specific acts does not apply when conduct is offered to prove bias or interest.
• Courts may restrict cumulative or marginal bias evidence, especially where the witness has already admitted the key facts.
• Bias and interest are distinct from impeachment by character for untruthfulness, prior convictions, prior inconsistent statements, and mere contradiction.
• Hearsay and Rule 404 character restrictions typically do not bar bias or interest evidence because it is used to show motive, not truth of statements or propensity.

Key Terms and Concepts

• Impeachment
• Bias
• Interest
• Extrinsic Evidence
• Collateral Matter
• Preliminary Showing