The word of the day is probative:
Etymology: < Middle French probatif convincing, founded on proof (late 14th cent.; French †probatif that can prove (1803)) and its etymon classical Latin probātīvus of or relating to proof < probāt- , past participial stem of probāre prove v. + -īvus -ive suffix.
1. Having the quality or function of testing; serving or designed for trial or probation; probationary. Obs.
2.a. Chiefly Law. Orig. Sc. Having the quality or function of proving or demonstrating; affording proof or evidence; demonstrative, evidential.
b. Sc. Law. Designating a document that contains its own authentication or evidence of validity without requiring additional verification. (OED)
"Judges routinely exclude evidence when its prejudicial effect outweighs its probative value—an odd phrase that can be explained with an example from Hitt’s article. Robert Leonard’s testimony that the language of graffiti and threatening e-mails was “consistent with” the language of the defendant’s writings in other contexts is the equivalent of a witness pointing to someone in the courtroom and saying, “That man could have been the assailant.” “Could have been” is hardly sufficient when the standard of proof is “beyond a reasonable doubt.” But when an “expert” like Leonard tells a jury with little knowledge of science or linguistics that the language in one sample is consistent with the language in another, the prejudicial effect far outweighs any probative value that the observation might have in identifying the murderer."
- James C. Raymond, President, International Institute for Legal Writing and Reasoning, New York City, letter to The New Yorker, 13 August 2012