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Published on: March 9, 2015
Application of random match probability calculations to mixed STR profiles
Todd Bille1, Jo-Anne Bright, John Buckleton
1U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives Laboratory, National Laboratory Center, 6000 Ammendale Road, Ammendale, MD, 20705.
Journal of Forensic Sciences
|February 22, 2013
Summary
This study compares statistical analysis methods for mixed DNA profiles, finding that random match probability (RMP) and likelihood ratio (LR) are more informative than combined probability of inclusion (CPI). These methods better utilize evidence data for accurate interpretation.
Area of Science:
- Forensic Science
- Genetics
- Statistical Analysis
Background:
- Increasing analysis of touch evidence yields more mixed DNA profiles in forensic laboratories.
- Statistical interpretation is crucial for assigning weight to evidence when an individual may be a contributor to a mixture.
Purpose of the Study:
- To compare the advantages and disadvantages of Random Match Probability (RMP) against commonly used methods: Combined Probability of Inclusion (CPI) and Likelihood Ratio (LR).
- To evaluate the informativeness and data utilization of RMP and LR compared to CPI in mixed DNA profile analysis.
Main Methods:
- Comparative analysis of statistical methodologies for mixed DNA profiles.
- Evaluation of data utilization (peak height, number of contributors, known contributors) across CPI, LR, and RMP methods.
Main Results:
- The Likelihood Ratio (LR) method is considered the most powerful among binary methods.
- Both Random Match Probability (RMP) and Likelihood Ratio (LR) methods effectively utilize observed data.
- The Combined Probability of Inclusion (CPI) method tends to be less informative and wastes data.
Conclusions:
- RMP and LR offer more robust statistical analysis for mixed DNA profiles compared to CPI.
- Forensic laboratories should consider RMP and LR for more accurate and informative interpretation of mixed DNA evidence.
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