Graphical tools for RFLP measurement quality assurance: laboratory performance charts

Forensic restriction fragment length polymorphism analyses typically provide two band size results at each genetic locus for each sample. In collaboration with the member laboratories of the Technical Working Group for DNA Analysis Methods, we have developed graphical techniques that compactly summarize even large numbers of such paired measurements. This paper provides a detailed description of the basic tool, a modified bivariate control chart for data from multiple samples and/or multiple loci. We demonstrate how various modifications and combinations of these "laboratory performance charts" can be used for quality control, quality assurance, and quality demonstration.