DNA testing is the most accurate method available to establish paternity. Its power is found in its ability to trace the pattern of inheritance for separate regions of the genetic material (chromosomes). From this information, it is possible to calculate a probability of paternity.

This number can reach 99.99999% in some cases. The percentage of random men of the same race that can be excluded as the biological father is also computed for every case.

Some companies test fewer chromosomal locations for the same price (or more) that GTL charge for 21 (20 identity markers plus one to confirm the sex of the person being tested). However, the statistics generated with fewer locations are not nearly as conclusive and in some cases can result in wrong conclusions, such as the father being excluded when, in fact, he is the true biological father.