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Green and Purple Abstract

Accuracy of evidence

  • DNA testing is the most accurate and reliable means of identity verification and parentage testing.  The degree of accuracy of the test will depend on the genetic diversity of the Sri Lankan population as well as the number of genetic locations (STR loci) which are tested. There is no mandatory number of STR loci required for a test, but the testing of nine STR loci or more is generally considered to be sufficiently accurate. We test up to 15 STR loci.

  • Accuracy in a test of familial relationships: A paternity or maternity test can prove with 100% certainty that an individual is not the biological parent of a child. However, no DNA test available can prove with 100% certainty that a man or woman is the biological parent of a child. Generally, a degree of certainty of over 99% is required to accept the paternity or maternity of an individual. DNA testing by Genetech typically proves paternity with at least 99.99% certainty. This is well in excess of the required accuracy.

  • Accuracy in criminal casework: In criminal casework, the demand for accuracy is greater, and the forensic scientist has to prove beyond a doubt that a suspect's DNA profile matches with that of the criminal. This involves expressing the probability of finding a random person in the population who might have this same profile. This probability is known as the Match Probability. This probability must be very low. When the Match Probability is lower, the accuracy of the conclusions of the DNA test is greater. There is no internationally agreed lower limit for this probability, but the result is generally accepted if it is lower than 1 in 1 billion. At Genetech, a sufficient number of loci can be tested to ensure that the Match Probability is lower than 1 in 10 billion.

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