Determining the Base Rate for Guilt

Research output: Contribution to journalArticle


A Bayesian assessment of the probability that the defendant in a criminal trial is guilty depends on the presumed base rate for guilt and the estimated likelihoods of the evidence. This article explores how the base rate shall be determined. Bayesian scholars have recommended a base rate of 1/N, where N is the number of ‘possible perpetrators’, but it is unclear how the reference class of possible perpetrators shall be defined. Several solutions are explored, and it is demonstrated that each solution leads to serious sacrifices in some fundamental principle of criminal justice. Some solutions lead to arbitrary assessments, or assessments that deviate from the facts. Other solutions fail to uphold an acceptable ratio between wrongful acquittals and wrongful convictions.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Law


  • Law, Jurisprudence
Original languageEnglish
Pages (from-to)15–28
JournalLaw, Probability and Risk
Issue number1
Early online date2017 Oct 27
Publication statusPublished - 2018 Mar 1
Publication categoryResearch