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Principles of Forensic DNA for Officers of the Court

Likelihood Ratio Estimates

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Likelihood ratio estimates compare the probability of observing a profile if known contributors were the source of the DNA in a mixture (numerator) to the probability of observing the mixed profile if other unknown contributors were the source of the DNA (denominator).

This approach is flexible and can handle differing assumptions as to the possible contributors to a mixed DNA profile. Conclusions are often stated in the following manner: Given the DNA evidence, it is 2 million* times more likely that the DNA profile from the mixed stain originated from the victim and suspect than if it originated from victim and one unknown, unrelated contributor.

* This number used arbitrarily for this example.

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