Presentation of evidence - Bias and interest

Learning Outcomes

After reading this article, you will be able to identify when bias or interest is relevant to the credibility of a witness, explain how bias and interest may be proved or challenged in court, and apply the rules for impeaching witnesses on these grounds in MBE-style questions. You will also understand the procedural requirements for raising bias and interest and the limits on admissibility.

MBE Syllabus

For MBE, you are required to understand how bias and interest affect the credibility of witnesses and the admissibility of evidence. This article focuses your revision on:

  • Recognizing bias and interest as grounds for impeaching a witness.
  • Methods for proving bias or interest, including cross-examination and extrinsic evidence.
  • Procedural requirements for raising bias or interest.
  • Limits on admissibility and when bias or interest evidence may be excluded.
  • The distinction between bias, interest, and other forms of impeachment.

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 key grounds for challenging the credibility of a witness in evidence law. The Federal Rules of Evidence and common law both recognize that a witness’s partiality or personal stake in the outcome may affect the weight of their testimony. Understanding how to raise, prove, and limit evidence of bias and interest is essential for the MBE.

Bias and Interest: Definitions and Relevance

Bias refers to any relationship, motive, or predisposition that may cause a witness to favor or disfavor a party. Interest means the witness has a direct personal stake in the outcome, such as a financial or legal benefit.

Key Term: Bias A tendency, motive, or relationship that may cause a witness to favor or disfavor a party, affecting the witness’s credibility.

Key Term: Interest A witness’s direct personal stake in the outcome of the case, such as a financial or legal benefit, which may affect their credibility.

Bias and interest are always relevant to credibility. Evidence of bias or interest may be introduced to show that a witness is not impartial and may be lying or shading their testimony.

Methods of Proving Bias and Interest

Bias or interest may be shown by:

  • Cross-examining the witness about facts showing bias or interest (e.g., family relationship, employment, financial stake, pending charges, or hostility).
  • Introducing extrinsic evidence (such as documents or testimony from others) if the witness denies or fails to admit the bias or interest on cross-examination.

Procedural Requirements

Before introducing extrinsic evidence of bias or interest, most courts require that the witness be asked about the facts showing bias or interest on cross-examination. If the witness admits the bias, further extrinsic evidence is generally not permitted unless the court finds good cause. If the witness denies or does not admit the bias, extrinsic evidence is allowed.

Key Term: Extrinsic Evidence Evidence from outside the witness’s own testimony, such as documents or testimony from other witnesses, used to prove bias or interest.

Limits on Admissibility

Evidence of bias or interest is generally admissible, but may be excluded if:

  • The evidence is unfairly prejudicial, confusing, or a waste of time (Rule 403).
  • The evidence relates to collateral matters with little relevance to the case.
  • The evidence is cumulative after the witness has admitted the bias.

Bias or interest evidence is not limited by the rule against hearsay, and is not subject to the same restrictions as impeachment by prior bad acts.

Distinction from Other Impeachment

Bias and interest are distinct from impeachment by character for untruthfulness, prior convictions, or prior inconsistent statements. Bias and interest focus on the witness’s motive or relationship, not their general honesty or past conduct.

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.

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 admits the bias, further extrinsic evidence is not allowed unless the court finds it necessary for clarity or fairness.

Exam Warning

Evidence of bias or interest is always relevant, but courts may limit repetitive or cumulative evidence. If a witness admits bias, do not assume you can always introduce more evidence on the same point.

Revision Tip

Always consider bias or interest as a possible ground for impeachment, especially when a witness has a relationship with a party, a financial stake, or a motive to curry favor.

Key Point Checklist

This article has covered the following key knowledge points:

  • Bias and interest are always relevant to witness credibility and may be used to impeach.
  • Bias is any motive, relationship, or predisposition to favor or disfavor a party.
  • Interest is a direct personal stake in the outcome, such as financial or legal benefit.
  • Bias or interest may be proved by cross-examination and, if denied, by extrinsic evidence.
  • Extrinsic evidence of bias is allowed if the witness denies or fails to admit the bias on cross-examination.
  • Evidence of bias or interest may be excluded if unfairly prejudicial, confusing, or cumulative.
  • Bias and interest are distinct from impeachment by character, prior convictions, or prior inconsistent statements.

Key Terms and Concepts

  • Bias
  • Interest
  • Extrinsic Evidence
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