NIST micronutrients measurement quality assurance program: Characterizing the measurement community's performance over time

The Micronutrients Measurement Quality Assurance Program (M(2)QAP) at the N ational institute of Standards and Technology was created in 1984 with the goal of improving among-participant measurement comparability for fat-solub le vitamin-related compounds in human serum. We recently described improved tools for evaluating comparison exercise data; we here extend and apply th ese tools to the evaluation of the measurement community's performance over the entire 15-year history of the M2QAP. We here display measurement perfo rmance characteristics for the 14 measurands most commonly reported by the M(2)QAP community. We column that among-participant comparability for total beta-carotene cannot be much improved without improving average long-term within participant measurement stability. We demonstrate that improved meas urand definition and/or identification of interferences may help participan ts improve comparability for many of the M(2)QAP's other commonly reported measurands. The reported measurement performance characteristics may be of interest to clinical, nutritional, and epidemiological studies involving an y of these measurands. The data analysis techniques utilized may be applica ble to other programs.