Why Do DNA Tests Say 99.9%

Have you ever wondered why DNA test results with a positive match say 99.9%? This seemingly high figure is not merely a random number but deduced after a thorough analysis of matching DNA samples.

If you want to figure out the answer, keep reading this article to figure out why DNA tests say 99.9%, and what it means.

DNA Test Interpretation

Contrary to what most people think, a paternity test result that says 99.9% doesn’t mean the identified individuals share 99.9% DNA. However, it means that there is a 99.9% probability that the identified individual is the father or mother of the child in question than any other random person.

More succinctly, the 99.9% is derived from the Combined Paternity Index (CPI) where the laboratory meticulously compares 21 genetic markers between the potential parent and the child. For a potential parent to be genetically related to the child, they must have at least 20 matching genetic markers to have a 99.9% probability of biological relation. On the other hand, if a significant number of genetic markers do not align, it indicates that the alleged father is not biologically related to the child.

Beyond that, if the minimum number of genetic markers are a match for a 99.9% paternity probability to be confirmed, the DNA test results will read “not excluded.” Conversely, if there is no paternal relationship confirmed, the result will read “excluded.” However, DNA test results won’t expressly say “you’re the father” — unless you’re watching a reality tv show.

Legal Liability Reasons

The 99.9% report on the test results also serves as a disclaimer for the test facility to mitigate potential legal liability. By expressly stating 99.9%, the test facility acknowledges that there is a 0.01% of error to avoid legal liability in a lawsuit.

However, the courts usually consider a DNA test result with 99.9% probability as enough evidence to establish a biological connection beyond a reasonable doubt.

99.9% Is a Standard for DNA Test

The 99.9% accuracy is considered a standard for DNA test results because of several factors:

Statistical significance

The percentage is used as a confidence interval due to the nature of the technology used in the DNA testing process. To put it into context, a report may have a probability of 99.9 % — but in actual sense, it could be 99.8% with an error of +/-0. However, the standard is rounded to 99.9% for practical reasons.

Genetic variation

It’s not possible for a parent and a child to share 100% of their DNA. Even if they share identical genetic markers, there will be specific genetic markers that won’t match. As a result, the genetic markers that are not identical account for 0.01% of genetic variation.

Conclusion

DNA tests are reported to be 99.9% accurate due to the high level of technology and methods used to analyze the samples. However, just like all scientific tests, the 0.1% error margin is left to show that accuracy does not mean 100% certainty due to certain limitations. Besides that, if you say a DNA test result is 100% accurate, you could open yourself to a lawsuit.