Generally, witness credibility is personal in nature and indeterminate in quality.  Witness credibility is often determined on the basis of the:

• personal characteristics of a witness; and
• presumptions that are held by a party who calls the witness about such witness.

Practically the factors that affect a witness’s credibility include:

• credibility of other witnesses in a case;
• plausibility of a theory and theme the witness is meant to support;
• order in which witnesses are called; and
• character of a jury.

Normally, the rules adopted for analyzing witness credibility are the same in both civil and criminal cases[i].  In all cases, a trial court has the discretion to give instructions on witness credibility[ii].  However in some appropriate cases, a trial court has additionally the discretion to give instructions regarding the interest of witnesses in the result of a trial.  Therefore, a witness’s interest and his/her relation or feeling toward a party are relevant matters in determining witness credibility.  In several situations, civil courts have observed that approved instructions on credibility that permit a jury to analyze the interest of a witness in the result of a trial and to find out a witness’s relation towards a party to a suit is proper and valid[iii].

Specifically, it is the duty of a party who calls a witness to establish witness credibility through extrinsic evidence introduction and direct or redirect examination.  Therefore for the purpose of impairing or supporting witness credibility, any party including a party calling him/her can examine the witness and introduce extrinsic evidence relevant to the issue of credibility[iv].

The question of witness credibility regarding an expert witness is a question to be determined by a jury.  But this does not mean that a jury is at liberty to disregard the testimony when from no reasonable point it is open to doubt[v].  Factors that help a jury in determining witness credibility include[vi]:

• appearance, manner, and behavior of a witness while giving testimony;
• apparent frankness and intelligence of a witness;
• capability of consecutive narration of acts and events by a witness;
• probability of a story related to a case;
• advantages gained by a witness in obtaining accurate information on a subject;
• accuracy or retentiveness of witness’s memory along with effect of lapse of time on memory;and
• intonation of witness’s voice and positiveness or uncertainty in testifying.

However witness credibility can be put in question, if a witness has made prior statements that are inconsistent with his/her trial testimony.  In such situations, it is the jury who decides upon whether a prior statement is materially inconsistent with witness testimony.

An exception to this general rule is that where testimony of a witness is clear, plain, complete, convincing and not incredible in light of general knowledge and common experience, the question of credibility will be presented to a court and not for a jury[vii].

[i] State v. Malmberg, 14 N.D. 523 (N.D. 1905).

[ii] State v. Pennington, 392 S.W.2d 5 (Mo. Ct. App. 1965).

[iii] Schamroth v. State, 84 Ga. App. 580 (Ga. Ct. App. 1951).

[iv] State v. Kelly, 207 N.J. Super. 114 (App.Div. 1986).

[v] Brown v. Ford Motor Co., 479 F.2d 521 (5th Cir. Ga. 1973).

[vi] People v. Jackson, 63 Cal. App. 2d 586 (Cal. App. 1944).

[vii] State v. Jones, 999 So. 2d 239 (La.App. 3 Cir. 2008).