Rules and principles governing the admissibility of scientific and expert evidence

United States v. Thomas, 134 F.3d 975, 978 (9th Cir. 1998) (reversing conviction and ordering new trial because even though the government's evidence of predisposition to engage in large-scale drug trafficking was weak, the trial court erred in failing to admit accused's evidence concerning his record of...Propensity, or character, is admissible if character is an essential element of a claim, charge, or defense.

Fed. R. Evid. 406 advisory committee's note ("When disagreement has appeared, its focus has been upon the question what constitutes habit" rather than on the admissibility of habit "and the reason for this is readily apparent. The extent to which instances must be multiplied and consistency of behavior maintained in order to rise to the...A course of conduct can constitute habit for purposes of Federal Rule of Evidence 406 and state counterparts to Rule 406 only if the conduct is highly regular or practically invariable.

Trammel v. United States, 445 U.S. 40, pin? (1980).The testifying spouse, not the accused spouse, is the holder of the marital testimony privilege, the adverse spousal testimony privilege.