 Another challenge to legal probabilism is the reference class problem. The reference class problem, originally formulated by Venn (1866), arises because the same event may belong to multiple reference classes in which the frequencies of the event in question are different. A common approach, given among others by Reichenbach (1935 [1949: 374]), is to rely on “the narrowest class for which reliable statistics can be compiled”. This may work in some cases provided reliable statistics are available. But what if someone belongs to different classes that are equally narrow?