Once analyzed at all locations, all paternity indexes are multiplied together to create the Combined Parentage Index (CPI). For an alleged father to be considered the child's father (to be 'not excluded' as the biological father) the CPI value must be at least 100. A CPI value of 100 means the probability of paternity is 99.0000%; a CPI value of 10,000 means a probability of 99.9900% and so on.
An alleged father is excluded as the biological father with as little as few as two to three mismatches (though there may be many mismatches). In the following example, the 3 mismatches would exclude the alleged father (he is not the biological father). Even though there are also 3 matches, they do not show a paternity relationship. Almost any two people will have at least some matches, but a father-child relationship will show matches at all locations. In this case, the combined index is 0, and the probability of paternity is 0%.
According to DNA paternity testing accreditation guidelines, a paternity report must show a CPI of greater than 100 (and a probability of paternity greater than 99.0%). Most courts, child support agencies, or other legal entities require an accredited paternity test report (see Legal Paternity Testing for more information). Immigration cases require a CPI value of 200 (99.5%) or better.
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