Str Analysis by Capillary Electrophoresis: Development of Interpretation Guidelines for the Profiler Plustm and Cofilertm Systems for Use in Forensic Science

Thresholds can be divided into two categories: analytical and match. An analytical threshold is the level that collected data is quantitatively evaluated. A match threshold is the level that analyzed data is used for match purposes. The analytical threshold can be chosen as the detected signal above baseline noise. Alternatively, an analytical threshold can be the same value chosen as the match threshold. A match threshold should be chosen based on studies that evaluate stochastic amplification. As such, a match threshold is the signal at or above which stochastic amplification is minimal, and will not result in allelic dropout. Allelic dropout occurs when one allele of a pair exhibits signal, whereas the other peak falls below detection. It can be considered “the line in the sand” for match purposes. Data falling below this threshold may not be suitable for match purposes; however, it can be used to exclude. Data at or above the match threshold, however, is of sufficient quality to determine a match. In choosing a match threshold, it should be remembered that forensic scientists must be both objective and conservative. Matches must be based on high quality data.