Which factor is measured by the Ashley rule in forensic medicine?

The Ashley rule is specifically concerned with estimating the age of skeletal remains, particularly through the measurement of certain skeletal features. Among the options provided, the correct choice relates to "sternum length." This measurement has been utilized in forensic anthropology to assist in determining the age of an individual based on the development and ossification of the sternum, as well as its overall morphological changes over time.

The rule highlights the relationship between skeletal dimensions and the age at death, providing a valuable method in forensic medicine for age estimation when only skeletal remains are available. The reason the other options aren't correct is that, while stature, bone density, and age estimation are important aspects measured in forensic medicine, the Ashley rule specifically focuses on the lengths and characteristics of the sternum to infer age. Thus, the correct answer emphasizes the relevance of sternum length in forensic age estimation applications.