A comparison of two methods for estimating measurement repeatability in morphometric studies
SummaryMeasurement repeatability is often reported in morphometric studies as an index of the contribution of measurement error to trait measurements. However, the common method of remeasuring a mounted specimen fails to capture some components of measurement error, and could therefore yield inflated repeatability estimates. Remounting specimens between successive measurements is likely to provide more realistic estimates of repeatability, particularly for small structures that are difficult to measure.Using measurements of 22 somatic and genitalic traits of the neriid fly Telostylinus angusticollis, we compared repeatability estimates obtained via remeasuring (where a mounted specimen is measured twice) versus remounting (where a specimen is remounted between measurements). We also asked whether the difference in repeatability estimates obtained via the two methods depends on trait size.Repeatability estimates obtained via remounting were lower than estimates obtained via remeasuring for each of the 22 traits, and the difference between estimates obtained via the two methods was generally greater for small structures (genitalic traits) than for large structures (legs, wings).Remounting specimens between successive measurements can provide more accurate estimates of measurement repeatability than remeasuring from a single mount, especially for small structures that are difficult to measure.