The ‘Horwitz ratio’—a study of the ratio between reproducibility and repeatability precisions in the analysis of foodstuffs

Abstract

This paper examines precision statistics from collaborative trials (interlaboratory method performance studies) reported between 1990 and 2000. The principal focus is on the ‘Horwitz ratio’ (s_R/s_r), the ratio of the estimated standard deviations of reproducibility (s_R) and repeatability (s_r) found for individual analytical procedures. A predictable ratio would be a valuable tool in assessing uncertainty and detection limit. While the median ratio observed was close to 2.0, a significant variation with a strong positive skew was observed, much of which could be attributed to particular types of analyte, test material, and analytical procedure.