Identification: meaning of the paternity index: practice question

A Forensic Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Forensic Medicine · Identification: meaning of the paternity index

Sample item

A DNA report on an alleged father gives a combined paternity index of 5000. How should this be interpreted?

AThere is a 1 in 5000 chance that he is the fatherBHe shares 5000 alleles with the childCThere are 5000 other men who could be the fatherDThe result is 5000 times likelier if he is the father than if an unrelated man is

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. The result is 5000 times likelier if he is the father than if an unrelated man is

The paternity index is a likelihood ratio comparing the probability of the observed genotypes if the alleged man is the father with that if a random unrelated man is. A value of 5000 gives strong support to paternity, and, combined with a prior probability, can be converted to a probability of paternity.

Option by option

A. There is a 1 in 5000 chance that he is the father
A high index supports paternity; it is not a 1 in 5000 probability of being the father.
B. He shares 5000 alleles with the child
The index is not a count of shared alleles.
C. There are 5000 other men who could be the father
The index does not count other possible fathers.
D. The result is 5000 times likelier if he is the father than if an unrelated man is (correct)
Correct. The index is a likelihood ratio and not a chance of paternity.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is D, The result is 5000 times likelier if he is the father than if an unrelated man is. The paternity index is a likelihood ratio comparing the probability of the observed genotypes if the alleged man is the father with that if a random unrelated man is.

Why is "There is a 1 in 5000 chance that he is the father" not the answer?

A high index supports paternity; it is not a 1 in 5000 probability of being the father.

Why is "He shares 5000 alleles with the child" not the answer?

The index is not a count of shared alleles.

Why is "There are 5000 other men who could be the father" not the answer?

The index does not count other possible fathers.

What concept does this question test?

It tests Identification: meaning of the paternity index in Forensic Medicine. A value of 5000 gives strong support to paternity, and, combined with a prior probability, can be converted to a probability of paternity.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Identification: meaning of the paternity index?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.