438 P.2d 33 (Cal. 1968)
Defendant and his wife were charged with and convicted of second degree robbery in violation of Cal. Penal Code §§ 211, 211(a), 1157. During trial, in an apparent attempt to bolster identification, plaintiff government called an instructor of mathematics as an expert witness and sought, through him, to establish that there was an overwhelming probability that the crime was committed by any couple answering the distinctive characteristics of the defendant and his wife. The witness testified, in substance, to the "product rule," stating that the probability of the joint occurrence of a number of mutually independent events was equal to the product of the individual probabilities that each of the events would occur.
Defendant successfully argued that, because trial by mathematics was irrelevant, immaterial, an invasion of the province of the jury, and based on unfounded assumptions so confusing to the jury and defense counsel, its use constituted reversible error.
The court reversed the judgment of conviction and held that defendant's trial by mathematics so distorted the role of the jury and so disadvantaged counsel for the defense as to constitute in itself a miscarriage of justice that mandated reversal.
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