Can the Validation Process in Forensic DNA Typing Be Standardized? Butler, Tomsey, and Kline Can the Validation Process in Forensic DNA Typing Be Standardized?

Validation of procedures used in forensic DNA typing is essential to ensure that reliable results can be obtained with a particular method and associated materials. Laboratories spend a significant amount of time performing validation of new DNA typing kits, software, and analytical instrumentation. As technologies are constantly evolving and new kits becoming available, the need to validate and implement new procedures is on-going. The wide variety of approaches and opinions that exist on the topic of validation make it challenging for a laboratory to deduce a minimum set of criteria for evaluation to ensure that a method can be relied upon to produce quality information. Through conducting a questionnaire of DNA caseworking and databasing laboratories, carefully surveying the literature, and interviewing representatives from a small lab, a large lab, and a contract forensic lab, we are attempting to establish a standardized model for validation that meets the needs of the forensic DNA typing community. The survey summaries found that a wide range of responses exist throughout the community making it difficult to define specific recommendations for minimum sample numbers given particular scenarios that would likely be adopted. A new website has been established as part of STRBase to collate the community’s past, present, and future validation studies in order to provide a dynamic resource with helpful information (se

FORENSIC SCIENCES Case Work Guidelines and Interpretation of Short Tandem Repeat Complex Mixture Analysis

Interpretation guidelines for short tandem repeat casework analysis are difficult to construct. As soon as a set of guidelines are developed, a new case evolves that does not fit the painstakingly written document. The casework analysts gather and amend the guidelines again, and again. This article seeks to demonstrate that general guidelines can be set and written such that it can be used for any detection format. Guidelines published by the Scientific Working Group for DNA Analysis Methods, a working group of DNA forensic experts in the United States, are used to set the format for the written protocol on interpretations. The rule "the interpretation of results in casework is a matter of professional judgment and expertise. Not every situation can or should be covered by a preset rule" is stressed. Development of minimum and maximum threshold values, heterozygote ratios, stochastic limits, and determination of major and minor components based on validation studies is discussed. The paper travels through setting criteria to evaluate internal lane standards and amplification controls. It continues with establishing ranges for interpretation and defining true alleles versus anomalies. Examples of a variety of profiles are given and the potential interpretation, using signal intensities and genetics. In addition, report writing strategies and wording routinely used by the Pennsylvania State Police DNA Laboratory System are given