Which statement about interpreting DNA evidence with a likelihood ratio is accurate?

Which statement about interpreting DNA evidence with a likelihood ratio is accurate?

• A. A high LR means stronger support for the non-contributor hypothesis.
• B. LR is a simple count of matching alleles.
• C. LR is the probability that the data were observed given a random match.
• D. A high LR means the data are more supportive of the contributor hypothesis than the non-contributor hypothesis.

Answer: (D)

In interpreting DNA evidence with a likelihood ratio, you’re comparing how probable the observed DNA data are under two competing explanations: that the person of interest contributed the DNA versus that someone else did (the non-contributor hypothesis). The likelihood ratio is the probability of the data given the contributor hypothesis divided by the probability of the data given the non-contributor hypothesis. A high LR means the observed data are much more likely if the contributor hypothesis is true than if the non-contributor hypothesis is true, so the data support the contributor hypothesis over the non-contributor one. That’s exactly what the statement expresses.

LR is not simply a count of matching alleles; it’s a ratio of probabilities conditioned on two hypotheses. Nor is it the probability of the data under a single “random match” scenario. The LR encapsulates how much more (or less) the data favor one hypothesis over the other.