Multiple observers, humidity, and choice of precision statistics: factors influencing craniometric data quality.

This study investigates three topics: (1) interobserver measurement error in craniometry, (2) the effects of humidity on craniometric measurements, and (3) the current status of estimators of measurement precision in craniometry and anthropometry. The results of the three-observer error analysis based on 24 linear measurements taken on 47 crania indicate that minor idiosyncratic variations in measurement technique can lead to high levels of statistical discrimination among the data produced by the different observers. The results of the humidity experiment substantiate the contention that increasing levels of relative humidity are associated with cranial expansion. The results of the comparison of 11 univariate precision estimators suggest that the combination of percentage agreement, the mean absolute difference, and Fisher's nonparametric sign test can give an instructive picture of the frequency, magnitude, and directionality of measurement imprecision. Information on the comparability of technique and measurement precision can then be used in the variable selection process prior to the application of multivariate statistical procedures to strengthen the substantive interpretation of craniometric data.