Each match receives a Paternity Index (PI) value. The paternity index is a way of measuring the strength of a particular match based in part on the relative uniqueness of the match. In our example, the child and alleged father each show an allele value of '12' at marker D2S1338, the paternity index value is 1.845. This is a reasonably strong match.
However, if the allele value of '12' at this location were a more common match, the PI would be smaller, say .0782. It's true the two participants match, and that could be because one is the biological father of the child, but it could also be they match simply because most people would match with this allele value at this location.
On the other hand, what if it was known that very few people would have an allele value of '12' at this location? The match would be stronger because it's rarer. In this case the PI value might increase; it might be 3.452, or 12.819 or 34.125, depending on the strength of the match. A PI value is 0.000 when there is no match between the father and child.
