Transposition fallacy
Definition
The error of treating the probability of the evidence given a hypothesis as though it were the probability of the hypothesis given the evidence. In the context of LR scales, the transposition fallacy arises when a jury reads 'strong support for the prosecution hypothesis' as meaning the defendant is probably guilty, rather than understanding it as a statement about the relative probability of the evidence.
Related terms
- Likelihood ratio (LR)
- The ratio of two conditional probabilities: the probability of the observed evidence given the prosecution's hypothesis (same source), divided by the probability...
- Bayes' theorem
- The mathematical rule that relates prior odds, the likelihood ratio, and posterior odds. In the odds form: O(Hp|E) = O(Hp) x LR....
- ENFSI guideline
- The European Network of Forensic Science Institutes Guideline for Evaluative Reporting in Forensic Science (2015, updated 2016). It defines the propositions framework,...
- Evaluative reporting
- A framework for expressing forensic conclusions in terms of the probability of the evidence given the prosecution hypothesis versus the defence hypothesis...
- Jeffreys scale
- A logarithmic scale for Bayes factors proposed by Harold Jeffreys in Theory of Probability (1961). Levels run from 'barely worth mentioning' at...
- Log10(LR)
- The base-10 logarithm of the likelihood ratio, sometimes called the weight of evidence (following I.J. Good). A log10(LR) of 1 corresponds to...
- Posterior odds
- The ratio of the probability of the prosecution hypothesis to the probability of the defence hypothesis after the forensic evidence is taken...
- Prior odds
- The ratio of the probability of the prosecution hypothesis to the probability of the defence hypothesis before the forensic evidence in question...
- Verbal equivalence scale
- A table that assigns a verbal phrase to a range of LR values or log10(LR) values. The phrase is used in written...
Explained in these topics
- Prior and Posterior Odds in CourtThe error of treating P(E|Hd) as equal to P(Hd|E). The probability of finding this evidence if the defendant is innocent is not the same as the probability of...
- Strength of Evidence and Likelihood Ratio ScalesThe error of treating the probability of the evidence given a hypothesis as though it were the probability of the hypothesis given the evidence. In the context...