NIST mixed stain studies #1 and #2: Interlaboratory comparison of DNA quantification practice and short tandem repeat multiplex performance with multiple-source samples

The Mixed Stain Study 1 (MSS1, Apr.-Nov. 1997) and Mixed Stain Study 2 (MSS 2, Jan.-May 1999) evaluated multiplexed short-tandem repeat (STR) DNA typin g systems with samples containing DNA from more than one source. These inte rlaboratory challenge studies evaluated forensic STR measurement, interpret ation, and reporting practice using well-characterized samples of very diff erent analytical difficulty. None of the relatively few errors reported in either exercise resulted in a false identification of a reference sources s everal errors in evaluating the unknown source in three-source samples woul d hinder matching the profile in any archival database. None of the measure ment anomalies reported is associated with any particular STR multiplex; al l DNA amplification anomalies are associated with inefficient DNA extractio n, inaccurate DNA quantitation, and/or analytical threshold policies.