# Underestimating the probability of coincidence

CITATION: Muller, M. A. 2014. Underestimating the probability of coincidence, Obiter. 35(2):173-187.

The original publication is available at http://reference.sabinet.co.za/document/EJC165863

Article

Coincidences are more common than most people might expect. It is quite possible that different pieces of evidence that seem to point in the same direction do so coincidentally. We come to the best possible conclusion about (say) the probability of guilt only after careful analysis of the combination of probabilities of the respective pieces of evidence has been performed in conformance with the principles of probability theory. Several methods are available for the evaluation and handling of such contingencies. Depending on the way a particular situation presents itself, Bayes’s theorem in one of its equivalent guises is often used. The danger in avoiding this type of reasoning is that incorrect conclusions may be drawn, believing that events are somehow beyond coincidence. When it happens in a court of law it may be extremely prejudicial to the defendant. Coincidences are best understood within the context of probability theory.