Development and usage of a NIST standard reference material for real time PCR quantitation of human DNA

National Institute of Standards and Technology SRM 2372 human DNA quantitation standard has been produced to support the need for a human-specific DNA quantitation standard in forensic casework and calibration of new quantitative polymerase chain reaction (qPCR) assays. The conventional DNA concentration has been assigned with one of the U.S. National Reference UV/Visible Spectrophotometers, assuming an absorbance of 1.0 at 260 nm equals 50 ng/μL of double stranded DNA. In addition, an interlaboratory study has been conducted, to verify that the SRM 2372 materials perform well in currently used DNA quantitation assays by the forensic DNA community. Each unit of SRM 2372 consists of three well-characterized DNA extracts. Component A is a single-source human male material derived from blood. Component B is a multiple-source human female material derived from blood. Component C was purchased as a purified unsheared genomic human DNA (Sigma-Aldrich Co., St. Louis, MO) obtained as a lyophilized human genomic extract and has both male and female donors. SRM 2372 is intended to enable the comparison of DNA concentration measurements across time and place. Manufacturers can use SRM 2372 to validate the values assigned to their own reference materials. Individual forensic laboratories can use SRM 2372 to validate DNA quantitation methods and to verify the assigned concentration of in-house or commercial DNA calibration standards.     

Is there a magical time boundary for diagnosing eyewitness identification accuracy in sequential line‐ups?

We examined whether eyewitness identification latencies for sequential line‐up decisions indicate an optimum time boundary that reliably discriminates accurate from inaccurate decisions. Participants (N = 381) observed a crime simulation and attempted two separate identifications from target‐present or target‐absent sequential line‐ups. As has previously been found with simultaneous line‐ups, the optimum time boundary identified did not reliably discriminate accurate from inaccurate identifications for both line‐up targets. Diagnosticity for choosers was, however, much higher at very high confidence levels than at lower levels. Possible reasons for why one index of signal strength (confidence), but not another (latency), might postdict accuracy within the sequential framework were presented.