Probability calculations When it is found that all the tested polymorphic markers match between an alleged father and a child, we consider paternity to be confirmed. It is then possible to calculate the probability of true paternity. To calculate the probability of paternity (according to Bayes theorem), the frequency of the alleles (variants of the specific polymorphic area) that are shared by a father and a child (type of the allele is found in laboratory tests) are taken into consideration. The frequencies of alleles differ in each ethnicity. The higher the frequency of the shared allele in a ethnic group, the higher the probability is that the sharing of the allele by a father and a child is random. For this reason, many polymorpic markers are studied (we use 16 polymorphisms as a standard) to minimalize the probability that alleles shared by an alleged father and a child are random.
For example, if in a distinct case the probability of paternity is calculated to be 99.995%, it means that a man is a child´s father with 99.995% probability and therefore there is still 0.005% probability (i.e. 100-99.995%) that a man is not a child´s father. In other words, there is 0.005% chance (1 man out of 20 000) that some other man can genetically be considered the child´s father. To ensure very accurate result, it is always necessary to analyze many polymorphic markers.
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