Prosecution Proposition (Hp)
Definition
The proposition advanced by the prosecution, typically asserting that the defendant is the source of the questioned material (e.g., 'the crime-scene DNA came from the defendant'). It occupies the numerator of the LR.
- Shorthand
- Hp
- Example content
- Crime-scene DNA came from the defendant
- Position in LR
- Numerator
- Used in
- Worked likelihood-ratio calculations
Common questions
What changes in a worked LR example when Hp is reworded from 'defendant' to 'a close relative of the defendant'?+
Because relatives share more alleles than unrelated individuals, the probability of observing the DNA profile under a relative-based Hp is higher than under an unrelated-stranger Hd, which lowers the resulting likelihood ratio compared to the standard unrelated-source comparison.
Is Hp always the higher-probability side of the ratio?+
No. The LR can favor either side depending on the evidence; a low LR (well below 1) actually supports Hd over Hp, so Hp is simply a label for which proposition sits in the numerator, not a guarantee that the evidence favors it.
Related terms
- Defence Proposition (Hd)
- The alternative proposition, typically asserting that someone else is the source (e.g., 'the crime-scene DNA came from an unknown, unrelated person'). It...
- Kernel Density Estimate (KDE)
- A non-parametric smooth probability density function fitted to a set of measurements by placing a kernel (usually Gaussian) over each data point...
- 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...
- Log-LR (Log Likelihood Ratio)
- The natural or base-10 logarithm of the LR. Log-LRs are additive for independent evidence types, making them convenient for combining across disciplines....
- Random Match Probability (RMP)
- The probability that a randomly chosen unrelated person from the relevant population would match the evidence profile by chance. A very small...