One question on many people's minds when they look into paternity testing is how accurate the paternity test results really are. No test can ever be 100% accurate but how accurate can you expect your paternity test results to be and what should you expect to see back from a DNA testing lab?
There are two types of results that you could potentially receive back from a paternity test, the first is called "exclusion". Exclusive paternity test results exclude a man from being a father of the child who was tested. This means that in the paternity test the DNA of the alleged father did not sufficiently correspond to the DNA of the child to consider him as a prospective father. In this case the result should be 100% accurate, if a man is excluded from being a child's father that means that there should be no way he could possibly be his or her father.
Inclusive paternity test results however are different, they refer to the likelihood that someone is the father of the child. If you are told by the DNA testing lab that the alleged father is "included" as the potential father of the child, it means that he was not excluded, and therefore could be the child's father. Although no test can ever be 100% certain, most paternity test results should yield at least 99% accurate results, preferably closer to 99.99%, that the alleged father is in fact the actual father.
The accuracy of paternity test results depends on how many loci (or points) are tested on the DNA segments of the alleged father and child; the higher the number of loci, the greater the accuracy that can be obtained.
To get the best results from your paternity test you should choose a laboratory that tests at least 13-16 loci and that excludes fathers who show a difference in two or more DNA patterns on the loci (this is known as the AABB standard that is used in accredited DNA testing labs).
In conclusion, although paternity test results can never be 100% accurate you should look for at least 99% accuracy and preferably closer to 99.99%.