Log-LR (Log Likelihood Ratio)
Definition
The natural or base-10 logarithm of the LR. Log-LRs are additive for independent evidence types, making them convenient for combining across disciplines. Positive log-LR supports Hp; negative supports Hd. Speaker comparison systems typically output log-LR scores directly.
- Definition
- Natural or base-10 logarithm of the LR
- Property
- Additive across independent evidence types
- Positive value
- Supports Hp
- Negative value
- Supports Hd
- Common output of
- Speaker comparison systems
Common questions
Why is the additive property of log-LR useful in casework?+
It lets an analyst combine the weight of evidence from several independent sources by simple addition, rather than having to multiply raw likelihood ratio values together.
Why do speaker comparison systems typically report log-LR instead of a raw LR?+
Raw LR values can span many orders of magnitude, and expressing the result on a log scale compresses that range into a more manageable, comparable figure.
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...
- Prosecution Proposition (Hp)
- The proposition advanced by the prosecution, typically asserting that the defendant is the source of the questioned material (e.g., 'the crime-scene DNA...
- 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...