@Neigh-Sayer @mmmfeet i wanna say that these probably have a decent rate of false positives if 1 in every 5 children is illegitimate.
@Neigh-Sayer @mmmfeet typically they do blood tests for paternity, no? Idk how accurate a mouth swab is, considering stuff like diy covid tests had a pretty big false positive rate to the point where many employers just wouldn't accept them. Drug tests done this way aren't always super accurate either AFAIK.
DIY tests seem like more of a thing where, if you get a positive result, it means you should go to the doctor and get a real test done. They're not meant to be definitive proof.
It shouldn't matter because you're looking for DNA which is present in all the cells. The reason why it's different compared to the Coof or drug tests is because in those cases you're looking for some signature in the test and that signature decays with time and is further dependent on where you actually collect the sample from. For example, the gold standard for a lot of drug tests is using hair follicles which can detect whether you've done drugs up to 3 months, compared to a urine test which can only detect for a few days. This is why you see a lot of criminals on probation with shaved heads.
For the DNA test, they take samples from two people, say, the father and the child, do PCR so they can rapidly multiply the genetic material, and then typically run those samples through gel electrophoresis to see whether their resulting dash patterns match, see below.
If they do match, that's strong evidence that whatever DNA you have in one person is also present in the other person. It holds up in court, being used to establish paternity for child support payments, as well as being used to place people at crime scenes by matching a suspect's sample from a skin/hair/blood/saliva/semen sample collected at the scene. The only way you could get out of that is by proving that the lab which ran the tests fucked up, which would be difficult to prove.