Error rates and observer bias in dental microwear analysis using light microscopy

Abstract

Despite the increased use of light microscopy in microwear analysis, studies that recognize observer error are scarce. Nonetheless, microwear analysis based on light microscopy may be more prone to observer bias than SEM or confocal microscopy. We measured observer error among five observers, who independently analyzed identical sets of dental wear surfaces on digital micrographs taken through a light microscope. For experienced microscopists, error in light-microscope-based microwear was of a similar magnitude to error rates for SEM-based microwear methods. Significant intraobserver error was rare among the most experienced observers and higher among inexperienced observers. However, because observers develop familiarity when repeatedly analyzing the same image, intraobserver error measured here and in other similar SEM studies may be artificially low. Interobserver error was highly significant and did not appear to diminish with experience. Nonetheless, the data collected by all observers was highly correlated. Essentially all observers found similar microwear differences between the species analyzed, even though the absolute values in the data were observer dependent. Going forward, microwear results will be more robust if observers adopt methods that ensure observer blindness, and avoid the common practice of combining data from different observers, and even from one observer when the observarions are separated by time and experience. Rather than using pre-published microwear databases of extant species as a basis for interpreting paleodiet, researchers may be better served by building shared microwear image libraries, with which observers could generate their own data for the basis of making paleodietary inferences. © Paleontological Society March 2012.