'False But Highly Persuasive:' How Wrong Were the Probability Estimates in McDaniel v. Brown?01 Jan 2009
In McDaniel v. Brown, the Supreme Court will review the use of DNA evidence in a 1994 trial for sexual assault and attempted murder. The Court granted certiorari to consider two procedural issues - the standard of federal postconviction review of a state jury verdict for sufficiency of the evidence, and the district court's decision to allow the prisoner to supplement the record of trials, appeals, and state postconviction proceedings with a geneticist's letter twelve years after the trial.
This essay clarifies the nature and extent of the errors in the presentation of the DNA evidence in Brown. It questions (1) whether the transposition of a conditional probability (of the DNA match given the defense hypothesis that a man unrelated to the defendant was the source of the semen on the victim's panties) amounted to a deprivation of due process and (2) whether the position of the Ninth Circuit Court of Appeals, the defendant, and various amici curiae that the probability of a match to any of four brothers should have presented rather than the probability of a match to a single brother.