Measuring the intercondylar shelf angle using radiographs: intra- and inter-observer error tests of reliability.

This study presents a test of intra- and inter-observer measurement error rates of the intercondylar shelf angle of the distal femur, as measured on lateral radiographs. This measurement is the central element of a method to determine racial affiliation from the distal femur. Four observers independently radiographed a set of 33 complete and partial femora from collections housed at the Joint POW/MIA Accounting Command, Central Identification Laboratory. Each observer then measured the intercondylar shelf angles in each radiograph, following the original method's guidelines. A supplementary inter-observer error test was conducted by four additional observers on one set of radiographs. Statistically significant differences were found for both intra- and inter-observer error based on the results of Student's t-tests, paired samples t-tests, and ANOVA analyses. The results of this study indicate that further experimentation should be undertaken in order to develop refined measurement techniques that may help improve standardization and reduce the observer error rates.

Evaluation of real-time PCR amplification efficiencies to detect PCR inhibitors.

Real-time PCR analysis is a sensitive template DNA quantitation strategy that has recently gained considerable attention in the forensic community. However, the utility of real-time PCR methods extends beyond quantitation and allows for simultaneous evaluation of template DNA extraction quality. This study presents a computational method that allows analysts to identify problematic samples with statistical reliability by comparing the amplification efficiencies of unknown template DNA samples with clean standards. In this study, assays with varying concentrations of tannic acid are used to evaluate and adjust sample-specific amplification efficiency calculation methods in order to optimize their inhibitor detection capabilities. Kinetic outlier detection and prediction boundaries are calculated to identify amplification efficiency outliers. Sample-specific amplification efficiencies calculated over a four-cycle interval starting at the threshold cycle can be used to detect reliably the presence of 0.4 ng of tannic acid in a 25 microL PCR reaction. This approach provides analysts with a precise measure of inhibition severity when template samples are compromised. Early detection of problematic samples allows analysts the opportunity to consider inhibitor mitigation strategies prior to genotype or DNA sequence analysis, thereby facilitating sample processing in high-throughput forensic operations.

Brief communication: ancient DNA prospects from Sri Lankan highland dry caves support an emerging global pattern.

Recovery of ancient DNA has become an increasingly important tool in elucidating the origins of past populations and their relationships. Unfortunately, many human skeletal remains do not contain original DNA amplifiable by polymerase chain reaction (PCR). Amino-acid racemization has proven to be a useful predictor of ancient DNA results. We analyzed the relative levels of amino-acid preservation and racemization of human samples from two highland dry-cave sites in Sri Lanka, and found that amino-acid enantiomer ratios were inconsistent with successful authentic DNA recovery. A review of the literature reveals that these results are consistent with a global pattern of poor DNA preservation in the tropics.