Section 20.17 Lay Witnesses and Expert Witnesses

• Library: Family Law Deskbook and 2014 Supp

G. (§20.17) Lay Witnesses and Expert Witnesses

The use of experts is sometimes unavoidable. Testimony regarding medical causation or complex business valuations almost invariably requires an expert. Often, however, a lay witness may be used to offer opinion testimony.

An expert may be allowed to testify “if scientific, technical or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue.” Section 490.065.1, RSMo 2000; see also Rule 56.01(b)(5). Most often, the expert opinions required in family law cases include valuation experts testifying as to the value of property or the income of the parties.

To offer an expert opinion, the witness must be qualified by “knowledge, skill, experience, training, or education.” Section 490.065.1. Expert witnesses can testify as to ultimate facts. Section 490.065.2. The expert must base the testimony on the facts of the case, and the facts must be of a type reasonably relied on and “otherwise reasonably reliable.” Section 490.065.3. Hypothetical questions are not required if a proper foundation is laid for the expert’s testimony. Section 490.065.4. But it is error to utilize a hypothetical question that does not fairly hypothesize the material facts reasonably relevant to the opinion. See:

Hobbs v. Harken, 969 S.W.2d 318 (Mo. App. W.D. 1998)

Rust v. Hammons, 929 S.W.2d 834 (Mo. App. W.D. 1996)

Wiley v. Pittsburg & Midway Coal Mining Co., 729 S.W.2d 228, 233 (Mo. App. W.D. 1987)

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