The Likelihood Ratio (LR) in forensic DNA evidence interpretation is defined as the probability of the evidence given the prosecution hypothesis divided by the probability of the evidence given the defence hypothesis. An LR of 1 000 000 means:
- A The suspect is one million times more likely to be the source than a random person from the population ✓
- B There is one million percent certainty of guilt
- C One in a million people in the population share the profile
- D The probability of a coincidental match is exactly 0.000001%
Correct answer: A. The suspect is one million times more likely to be the source than a random person from the population
Explanation
The Likelihood Ratio expresses the evidential weight as how many times more probable the observed DNA evidence is if the suspect is the source compared to if a random unrelated individual from the population is the source. An LR of 1 000 000 means the evidence is one million times more likely under the prosecution hypothesis than the defence hypothesis. It does not directly state probability of guilt (which requires prior probability — the prosecutor's fallacy), nor is it equivalent to population frequency without context.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
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Written and medically reviewed by the StethoPrep medical team.