Family oral history may be useful in a scientific investigation as a pointer to suggest lines of inquiry, or to support other, more substantial evidence. From a legal standpoint admissibility is the test which determines whether the evidence may be considered, e.g. it is information from a source which the law permits in a legal proceeding and is material and relevant to the issues presented, and because of the nature of the evidence, whether greater or lesser weight should be accorded to it. Hearsay is testimony offered by someone who does not have personal knowledge that the testimony is true. A witness cannot be cross-examined on hearsay because the witness only knows what he has been told. For that reason, hearsay is inadmissible unless it falls within certain limited exceptions.
Oral history is inherently hearsay and therefore inadmissible.