A Police Department posed the following question to Analysis & Inference: are similar answers on a promotion exam coincidences, or did they establish cheating by a defendant and another officer?
Analysis & Inference developed a statistical model of question-answering. Then, we used a computer simulation of 100,000 people taking the test to determine the probability of similar answers under two distinct hypotheses: no cheating, and cheating.
The probability of matching answers was several orders of magnitude greater under a hypothesis of cheating.
