Interobserver variation affects accuracy of inference in life history studies using cementochronology.

Objective: Cementochronology is a method for assessing chronological age and identifying other life-history parameters (LHPs) from incremental lines of acellular extrinsic fibre cementum (AEFC) in most mammalian teeth. The aim of this study is to question the accuracy of this technique when used as a stand-alone age estimation method, and to examine how the number of observers may alter accuracy.

Design: This research is based on an extant clinical study conducted on 10 human teeth with the patients' anamnestic data. Nine observers used cementochronology to count AEFC incremental lines from 82 digital images. The counting was performed at three non-standardised areas on each image, totalling 246 counts per observer. Resultant observer counts were compared using the coefficient of variation method.

Results: The mean deviation of cementum estimated age from known chronological age of the participants in the study is 5.2 years.

Conclusion: Our study shows that further critical examination of the current cementochronology technique is essential, due to the subjectivity of line counting. The number of skilled observers in the study may improve the overall accuracy of the technique. These issues have wider implications, as many researchers rely on accurate scientific inferences being made by cementum-based studies to support or refute overarching demographic models and grand evolutionary narratives grounded by life history theory. Until this issue is resolved cementochronology should only be used alongside other age estimation methods.