A Robust Method for Calculating Precision for Interlaboratory Studies with a Staggered-Nested Design

Outlier testing and elimination can be avoided via application of robust estimators. Amongst robust estimators, the Q/Hampel method displays the best performance (in terms of breakdown point and efficiency). While the formulas and correction factors for Q/Hampel in the case of the design with two variance components (e.g. within- and between-laboratory variance) have already been made available, corresponding formulas for other designs have not. A case in point is the staggered-nested design, which is a highly efficient design for e.g. the estimation of intermediate precision in method validation studies. Accordingly, the formulas and correction factors for the use of Q/Hampel in the staggered-nested design are provided here.