How is the Probability of Paternity determined?

The Probability of Paternity is the overall likelihood of paternity expressed as a percentage. It is computed using a mathematical formula that considers all of the evidence in a case—both genetic evidence (Combined Paternity Index) and the non-genetic evidence (Prior Probability). In this computation, the Combined Paternity Index is “converted” to a percentage based on an unbiased assumption that the Prior Probability is 50% (or 0.5)—a neutral value which means that, prior to DNA testing, the alleged father is considered equally likely to be the biological father as he is not to be the biological father. A DNA test result with a Probability of Paternity of 0% means that the alleged father is excluded, or cannot be the biological father. A DNA test result with a Probability of Paternity of 99% or greater means that the alleged father is most likely the biological father.

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