What are the chances that the DNA on the knife came from someone - ProProfs
     

What are the chances that the DNA on the knife came from someone other than the suspect?
A man has been stabbed to death at his home in a city, and a suspect is on trial for the crime. The murder weapon has been recovered, and a sample of DNA has been obtained from the handle. The suspects DNA profile matches that on the handle. An expert witness says that the probability of anyone else being a DNA match is 1 in 3 million.



A. 1 in 3 million
B. More than 1 in 3 million
C. Less than 1 in 3 million
D. We don't have enough information to say

This question is part of How well would you do on a jury?

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1 Answer

John Smith

John Smith

Answered on Apr 29, 2017

More than 1 in 3 million

1 in 3 million is the likelihood that any innocent person in the population has a DNA profile matching that found on the knife. If the population is greater than 3 million (as an example, the UKs population is around 60 million), more than 1 person will have that profile. Hence, the odds that the DNA on the knife did not come from the suspect must be higher than 1 in 3 million. If you thought the odds were 1 in 3 million, you fell for the Prosecutors Fallacy.

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