There are many safeguards in place to be sure you get the correct results. The problem is not everyone orders a paternity test every day, so many customers have not been told about the differences in the levels of testing. There is no government oversight in DNA testing. Accreditation programs such as the AABB, and ISO had to step in and make sure measures are in place to be sure that testing is done accurately.
Because there is no government oversight, it is still not illegal for someone to run paternity tests, and issue reports from those test, when their laboratory has never been inspected by anyone to check whether they are performing the test accurately, or even at all.
Paternity Testing Corporation is accredited by many programs including the AABB family relationship testing accreditation program, and ISO17025 International standard for organization forensic accreditation program.
A paternity index of 100 is 99%, a paternity index of 1000 is 99.9%, and a paternity index of 10,000 is 99.99%.
Although there is a small change in the number, a result of 99.99% is 100 times more accurate than a result of 99%. Here is how it works. For every DNA location tested, on a positive report, there is a number at the end of the column. This number represents how common that particular size of DNA is in the population group. For example, if the father was Thai, there would be a Thai database that shows which DNA is common and which is not. All of these calculate into a paternity index. The paternity index directly translates into a percentage. If you had a index of 99, you would take 99/100=99%, if it was 10,000,000 it would be 10,000,000/10,000,001, which would be 99.99999%.
A test of 99% could give incorrect results about who the real father is. Companies can sell these kinds of tests because it is not yet illegal, and they are cheap to buy. What this number actually represents is 1 in 100 men from the population group tested, such as Thai, will test positive to be the father. When you are trying to figure out who the father is of a child, a one in one hundred chance that you could test positive as being the father anyways, is not the best answer. Customers believe the answer because it is DNA evidence.