What is the test for admissible evidence of prior criminal activity?

Other jurisdictions have expressed the same rule. "It is well-established in [the federal second] circuit that evidence of subsequent similar acts, including other crimes, is admissible in the discretion of the trial court if 'it is [7 Cal.4th 426] substantially relevant for a purpose other than merely to show defendant's criminal character or disposition', [citation], and its probative worth outweighs its potential prejudicial impact. [Citations.]" (United States v. Cavallaro (2d Cir.1977) 553 F.2d 300, 305, italics added.) " 'Both prior conduct and subsequent conduct may be relevant ..., depending on the circumstances and the probative value of the collateral conduct sought to be proven.' " (People v. Tipton (1980) 78 Ill.2d 477, 36 Ill.Dec. 687, 691, 401 N.E.2d 528, 532, and cases cited, italics in original.)