A sibling study is where you obtain DNA samples from additional brothers or sisters of the same alleged father to determine if the biological father for the tested group is common. The test is enhanced if samples are provided from each child’s mother.

The results of a sibling study report the percentage of probability of their relationship. If it is known that the tested subjects are from the same mother, then a 50% response (half siblings) would indicate that they have different fathers, and 99% would indicate that they have the same father (full siblings). Results can vary from .001 (no relationship) to 99% (full sibling). This is a very difficult test, and most labs require several weeks to complete the test, the hand calculations, and the report.