John Venn stated in 1876 that "every single thing or event has an indefinite number of properties or attributes observable in it, and might therefore be considered as belonging to an indefinite number of different classes of things", leading to problems with how to assign probabilities to a single case.
He used as an example the probability that John Smith, a consumptive Englishman aged fifty, will live to sixty-one.
An individual thing or event may be incorporated in many reference classes, from which different probabilities will result.
"[2] There has also been discussion of the reference class problem in philosophy[3] and in the life sciences, e.g., clinical trial prediction.
Suppose we wish to assess the probability of guilt of a defendant in a court case in which DNA (or other probabilistic) evidence is available.
We could say that the crime occurred in a city of 1,000,000 people, of whom 15% meet the requirements of being the same sex, age group and approximate description as the perpetrator.
We could cast the net wider and say that there is, say, a 25% chance that the perpetrator is from out of town, but still from this country, and construct a different prior estimate.
Charles Shonubi, a Nigerian drug smuggler, was arrested at JFK Airport on Dec 10, 1991, and convicted of heroin importation.