What is STRmix?

STRmix is a type of forensic software used to help interpret complex DNA mixtures.

It is known as a probabilistic genotyping system. Rather than simply comparing DNA profiles, STRmix uses statistical modelling to evaluate whether a person’s DNA may have contributed to a mixed sample containing genetic material from multiple individuals.

In Australia and New Zealand, STRmix is widely used in forensic laboratories to assess mixed DNA profiles. Other jurisdictions may use different probabilistic genotyping systems, each applying its own modelling approaches and assumptions.

STRmix does not identify a person in the same way as a clear single-source DNA profile. Instead, it calculates the strength of support for the proposition that a person’s DNA contributed to the mixture compared with the proposition that it did not.

The software relies on complex mathematical models, population data, and assumptions about the number of contributors and the behaviour of DNA during analysis. The results are typically expressed using statistical measures such as likelihood ratios.

While STRmix is a scientifically advanced tool, its outputs depend on the quality of the DNA data and the assumptions applied during analysis. Different modelling decisions or input parameters can influence the outcome.