Analysis of Positive Control STR Experiments Reveals that Results Obtained for FGA,D3S1358, and D13S317 Condition the Success Rate of the Analysis of Routine Reference Samples

About 120,000 reference samples are analyzed each year in the Forensic Laboratory of Lyon. A total of 1640 positive control experiments used to validate and optimize the analytical method in the routine process were submitted to a multivariate exploratory data analysis approach with the aim of better understanding the underlying sources of variability. The peak heights of the 16 genetic markers targeted by the AmpF?STR^® Identifiler^® STR kit were used as variables of interest. Six different 3130xl genetic analyzers located in the same controlled environment were involved. Two major sources of variability were found: (i) the DNA load of the sample modulates all peak heights in a similar way so that the 16 markers are highly correlated, (ii) the genetic analyzer used with a locus‐specific response for peak height and a better sensitivity for the most recently acquired. Three markers (FGA, D3S1358, and D13S317) were found to be of special interest to predict the success rate observed in the routine process.