NIST Micronutrients Measurement Quality Assurance Program: Characterizing individual participant measurement performance over time

The mission of the Micronutrients Measurement Quality Assurance Program (M(2)QAP) at the National institute of Standards and Technology is enhanced interlaboratory measurement comparability for fat-soluble vitamin-related measurands in human serum. We recently described improved tools for evaluating individual participant measurement performance in single interlaboratory comparison exercises; we here apply and extend these tools to the evaluation of participant performance over the entire 15-year history of the M(2)QAP. We describe and illustrate a set of interconnected graphical reporting tools for identifying long-term trends and single-exercise events. We document and discuss recurrent patterns we observe in the measurement performance characteristics for M(2)QAP participants. The graphical analysis techniques utilized may he applicable to other interlaboratory comparison programs.