This ratio of probabilities is then used by juries or judges to draw inferences or conclusions and decide legal matters.
[1] Jurors and judges rely on the strength of a DNA match, given by statistics, to make conclusions and determine guilt or innocence in legal matters.
In a single-source DNA profile, the statistic used is termed a random match probability (RMP).
[3] Other statistical tools to describe DNA mixture profiles include likelihood ratios (LR) and combined probability of inclusion (CPI), also known as random man not excluded (RMNE).
[4] Computer programs have been implemented with forensic DNA statistics for assessing the biological relationships between two or more people.
[4] RMP can only be used as a statistic to describe the DNA profile if it is from a single source or if the analyst is able to differentiate between the peaks on the electropherogram from the major and minor contributors of a mixture.
If the DNA mixture contains a ratio of 4:1 of major to minor contributors, a modified random match probability (mRMP) may be able to be used as a statistical tool.
For calculation of mRMP, the analyst must first deduce a major and minor contributor and their genotypes based on the peak heights given in the electropherogram.
LRs consider probabilities of events happening and rely on alternative pairs of hypotheses against which the evidence is assessed.
For example, if the CPI calculated is 0.5, this means that the probability of someone chosen at random in the population not being excluded as a contributor to the DNA mixture is 0.5.
Therefore, CPI is a statistical tool that can be used to provide weight or strength to evidence when no other information about the crime is known.