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The DNA Testing firm in the below article claims that its tests were "99.99 per cent" accurate.

http://www.telegraph.co.uk/news/uknews/1322077/False-DNA-test-led-father-to-reject-daughter.html

Googling "dna test accuracy" has led to numerous websites many of which claim an accuracy of their DNA testing to be 99.9%, with some even 100%!

How does a firm calculate this percentage accuracy? It seems to me that experimental data would not be useful in determining this percentage accuracy as there is no way to really confirm the fact that Bob is the son of John and vice versa as that is what we're trying to find out. Do they do so by factoring in slight inaccuracies in the laboratory procedure?

Acquiring experimental data would not be useful as I described above for paternity testing, a useful application of DNA testing, but could, to my knowledge, be used to determine the percentage accuracy of DNA testing in the recognition sense. By DNA testing various cells of the same person, and then seeing how many of them result to be from the same individual according to the DNA test (understanding that scientifically every cell should have the same DNA but then experimentally acquiring results that show that 999 in every 1000 cells show to link back to the same person) seems to be a working method...Is this how it works? Is this the notion conveyed with the idea of the percentage accuracy of DNA testing?

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Essentially, yes. These tests are usually based on enzymes that replicate DNA, and they have a certain (small) probability of getting a base wrong now and then. You can estimate the error frequency by doing many repetitions of sequencing of the same DNA sample and counting the number of discrepancies. Of course, this assumes that there are no systematic errors, only random variation, which may not be entirely true.

The Sanger sequencing technique is estimated to have error rates on the order of 0.001% (or, is 99.999% correct). I don't know exactly how these firms calculate their numbers, but I would guess it is similar.

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