Estimating the age at death in the adult skeleton is problematic owing to the biological variability in morphological age indicators and the differential response to environmental factors over an individual's life. It is becoming increasingly important for anthropologists to improve age estimates through the use of multiple age indicators and various modalities of assessment (e.g., macroscopic, microscopic, and radiological). Lack of instructional texts describing how to prepare histological samples and evaluate bone under the microscope has been a restricting factor in the widespread use of current histological methods within the field of forensic anthropology. The limited use of histological methods for age estimation often lies in the misunderstanding that the preparation and evaluation of cortical bone thin sections is a highly technical and an expensive endeavor. Like any method of age estimation, the researcher/practitioner must be guided through the analytical process to ensure reliable and repeatable results. This chapter provides a step-by-step instructional guide in the preparation and evaluation of histological samples removed from the sixth rib for histological age estimation.

Histological analysis of bone tissue has been used to explore a variety of questions relating to age-at-death, habitual behaviors, health, and nutritional stress. Identification of intact and fragmentary osteons is of key interest to many researchers in these studies, yet the definitions of these features vary between researchers making crossstudy comparisons problematic. Furthermore, histological variable definitions are often ambiguous or require subjective classifications by the observer. As a result, and as indicated by previous studies, observer error and misclassification of certain variables, namely intact and fragmentary osteons, can be significant. This study proposes new definitions for intact and fragmentary osteons that are designed to limit observer subjectivity and also explore efficacy of combining osteon types into one variable. A sample of 30 6th rib cross-sections from a modern forensic population was used to test the validity of the proposed definitions. Observations of intact osteon population density (OPD(I)) and fragmentary osteon population density (OPD(F)) were made by three observers for each cross-section. These observations were used to explore the interobserver error associated with the proposed definitions and determine if combining variables into one variable (OPD) mitigates persisting classification difficulties.Results indicate that the proposed definitions significantly reduce interobserver error and misclassification of intact and fragmentary osteons. However, the interobserver error associated with fragmentary osteons is still high. Evaluation of the variables independently indicates that combining variables has potential to reduce the predictive strength of an age estimation model and the ability to interpret age-related bone remodeling.

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