Applying Internal Validation Guidelines for Expanded STR Loci Kits

• NCJ Number: 250586
• Date Published: January 2017
• Length: 4 pages
• Grant Number(s): 2011-DN-BX-K564
• Agencies: NIJ-Sponsored
• Publication Type: Report (Technical Assistance); Report (Grant Sponsored); Instructional Material

Annotation

This report discusses the application of internal validation guidelines for expanded STR loci kits.

Abstract

The familiar 13 Combined DNA Index System (CODIS) core loci expanded to 20 CODIS core loci as mandated by the FBI on January 1, 2017. These additional loci were selected based on feedback obtained from the CODIS Core Loci Working Group and consortium testing of new Short Tandem Repeat (STR) kits at 11 laboratories across the United States. Due to conformance with previous DNA profiles already stored in the CODIS database, the original 13 loci will be maintained as required. The new expansion includes loci aimed to become more compatible with international databases, increase the power of discrimination, and reduce the opportunity for accidental matches as the CODIS database expands in size. Because of this FBI mandate, the participating CODIS laboratories must internally validate an expanded STR loci kit for implementation in 2017. Information can be extrapolated from the Scientific Working Group on DNA Analysis Methods (SWGDAM) basic recommended internal validation studies. An overview of SWGDAM recommended studies (2012) focuses on known and non-probative evidence samples or mock evidence samples, sensitivity and stochastic studies, precision and accuracy, mixture studies, and contamination assessment. After validation design, running samples, and collecting data, laboratories must analyze the data in order to extract trends, noise levels, appropriate threshold settings, and other valuable conclusions. This process is also discussed in this report. 13 references