The problem of age estimation: A study using rhesus monkeys ( Macaca mulatta )

Accurate estimation of chronological age for animals of unknown birth date is important in a variety of circumstances. This is particularly true for non‐human primates and especially true for rhesus monkeys. Data, useful for this purpose, have been organized in a variety of ways. The purpose of this paper is to duplicate some of these methods and to check their accuracy. In general, three methods of organizing data were used. The parameters for each method were estimated from one group of rhesus monkeys. Accuracy of age estimation was determined from a closely related, second group which had been raised under approximately the same conditions and from a third group of unrelated monkeys raised under different conditions. Some methods provided better estimations than others, but none was absolutely accurate. The analyses indicate that the degree of inaccuracy of a method should be determined on a sample which is independent of the one from which the parameters were estimated.