Ivey v. Commonwealth

Alfred Ivey, Jr. (defendant) was charged with rape of a minor. The rape resulted in a child, and the Commonwealth of Kentucky (plaintiff) introduced a DNA paternity test into evidence. The paternity test involved three steps. First, the examiner compared 15 locations on the child’s and Ivey’s DNA to see whether Ivey could be excluded as a potential parent. The examiner found matches between the DNA at all 15 locations, so Ivey was not excluded. The examiner next calculated a paternity index, which measured the likelihood that a union between Ivey and the child’s biological mother would produce a child with the child’s DNA markers. Ivey’s paternity index indicated that Ivey was 11,900,000 times more likely to be the father than a randomly selected male of the same race. The third step in the test calculated Ivey’s probability of paternity, based on his prior probability of paternity combined with the paternity index. The prior probability of paternity indicates the probability, prior to DNA testing, of the potential father being the child’s biological father. In general, this prior probability can vary based on factors including the potential father’s access to the child’s biological mother, the parties’ fertility, and the date of conception. However, in criminal cases, a standard prior probability of 50 percent is used to calculate a defendant’s probability of paternity. Using that 50 percent prior-probability figure, Ivey’s probability of paternity was 99.9999 percent. Even using much lower prior probabilities in the calculation, Ivey’s probability of paternity always exceeded 99.99 percent. Ivey was convicted, and he appealed to the Kentucky Supreme Court.