Defence Hypothesis (Hd)
Definition
The proposition advanced by the defence, typically that the material came from an unknown unrelated individual or that the defendant was not present. The analyst must choose a realistic Hd; an implausible Hd inflates the LR artificially.
- Symbol
- Hd
- Typical content
- Material came from an unknown unrelated individual
- Position
- Alternative to the prosecution hypothesis in a likelihood ratio
- Selection standard
- Must be realistic, given the case circumstances
- Risk of poor choice
- An implausible Hd artificially inflates the likelihood ratio
Common questions
Who is responsible for formulating the defence hypothesis used in a likelihood ratio calculation?+
The analyst formulates a hypothesis that is realistic given the case circumstances, often in consultation with case information from both sides, though the actual defence legal team may propose an alternative version reflecting their theory of the case.
What makes a defence hypothesis unrealistic, and why does that matter?+
An unrealistic Hd is one with no support in the case facts, such as proposing a relative as the alternative source when there is no such relative in the picture, which understates the true probability of the evidence under Hd and produces a likelihood ratio stronger than the evidence actually justifies.
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...
- 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...
- Prosecution Hypothesis (Hp)
- The proposition advanced by the prosecution, typically that the defendant is the source of the recovered material or was present at the...
- Prosecutor's Fallacy
- The error of treating the RMP (or its reciprocal) as the probability that the defendant is innocent, or as the probability that...