Three factors relevant to determining the admissibility of expert opinion evidence ... which are also part of the common law in England and Wales are: (1) “whether the subject matter of the opinion is such that a person without instruction or experience in the area of knowledge or human experience would be able to form a sound judgment on the matter without the assistance of a witness possessing special knowledge or experience in the area” (2) “whether the subject matter of the opinion forms part of a body of knowledge or experience which is sufficiently organized or recognized to be accepted as a reliable body of knowledge or experience, a special acquaintance with which by the witness would render his opinion of assistance to the court” and (3) “whether the witness has acquired by study or experience sufficient knowledge of the subject to render his opinion of value in resolving the issues before the court”

A Flowchart showing criteria of admissibility in Australian law

admissible evidence isevidence which the trial judge finds is useful in helping the trier of fact (a jury if there is a jury, otherwise the judge), and which cannot be objected to on the basis that it is irrelevant, immaterial, or violates the rules against hearsay and other objections. Sometimes the evidence which a person tries to introduce has little relevant value (usually called probative value) in determining some fact, or prejudice from the jury's shock at gory details may outweigh that probative value. In criminal cases the courts tend to be more restrictive on letting the jury hear such details for fear they will result in "undue prejudice." Thus, the jury may only hear a sanitized version of the facts in prosecutions involving violence.

The Civil Evidence Act 1968 and the Police and Criminal Evidence Act 1984 set out requirements for the admissibility of certain types of computer-produced evidence. As part of the conditions of admissibility these statutes lay down minimum authentication requirements. However, the Acts arguably only apply to evidence that would otherwise be excluded as hearsay and not to direct or real evidence; in such a case the law contains no clear statements as to how that evidence should be authenticated. The paper argues that admissibility and authentication are separate issues, and that the failure to treat them independently gives rise to needless confusion. This failure also directs attention away fmm the urgent need for clear rules governing the authentication of computer evidence. The lack of such provisions is a substantial obstacle to all types of digital communication and data storage.