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STR Data Analysis and Interpretation for Forensic Analysts

Mixtures with Indistinguishable Contributor(s)

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Items falling into this category include non-intimate samples such as swabs from a windshield, sidewalk, wall, floor, weapon, etc. This category applies to mixtures that are not included in the two categories described above.

These mixtures are typically the most difficult category to interpret. In general, the interpretation of two-person mixtures (where each person donates half of the DNA) will not be aided by estimating percent contribution or percent peak height ratios.

Applying statistical interpretation is more simplistic with one contributor (e.g., single source samples or mixtures where a major component can be defined or inferred). Statistical evaluation of complex mixtures involves the use of the likelihood ratio or probability of inclusion/exclusion.

Read more about the likelihood ratio in course: Population Genetics & Statistics.

Read more about the probability of inclusion/exclusion in course: Population Genetics & Statistics.

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