Paternity Test Accuracy
100% seems like the benchmark for accuracy in our modern world. After all, a pregnancy test can detect pregnancy with 99% accuracy rate. Through in some cases DNA can be determine near 100%, there is no way to prove paternity with 100% accuracy and in some cases even 99%.
The best way to understand why DNA cannot be measured more accurately is to compare it to the lottery. The chance that one person would choose all six winning numbers is slim, so more often more than one winner is picked. A person has unique genetic make-up, so the odds of that person sharing that DNA profile are slim to none. That said, the genetic markers used to test DNA are limited, so it is possible ,though it would be extremely rare, for two random people to have enough similar markers for a false report to happen. To account for this rare occurrence labs test more genetic markers so they can say that the possibility of a second party being the paternal father would be extremely small.
It is important to understand that even when a lab finds and exact genetic match between a child and father, there is always a theoretical possibility that another possible father mat exist. However, that theoretical father would have to be someone with similar genetic markers, which in itself is rare. When the lab has determined the probability of paternity to an extremely high degree most courts disregard the possibility of another father unless proof is brought fourth that would suggest otherwise.
For this reason, when you read a DNA report and it says that “John Doe” can’t be excluded as a child’s father of the child in question, but paternity has been established with 99.99% probability, these results should be considered 100% accurate.