Abstract
A new approach to assessing percent measurement error (%ME), using an old sta- tistical technique (Model II Analyses of Variance and Covariance: ANOVA/ANCOVA), was developed using both weight and linear measurements made three times each on 87 freshwater snails (Cipangopaludina chinensis; Vivipariidae). Variability of each measurement, as well as co- variability between pairs of measurements, was partitioned into among- and within-snail (i.e., measurement error) components. The %ME varied by two orders of magnitude across the ten measurement variables considered. Shell weight had the lowest %ME (0.059%), while body whorl height had the highest (3.88%). There was a low correlation between %ME and the among-snail coefficient of variation for each variable (r = -0.28; P > 0.20). Within-snail correlations between pairs of measurement variables were uniformly low (r,ilhin ' 0.20), while among-snail correlations were generally very high (r = 0.74 to 0.99) due to the large size range of snails in the sample. In any morphometric study, if %ME is found to be high for a particular variable, it should either be deleted from the study or remeasured a number of times on every individual to be included in the dataset. (Measurement error; morphhometrics; model II ANOVA/ANCOVA.)
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