Declines in function1 are common manifestations of aging in many phyla (Arking, 1998). As functional senescence is thought to drive the increasing risk of death with age, understanding functional senescence is important for understanding aging. Experimental investigation of functional senescence requires one to quantitate and compare age-dependent declines in function between cohorts. Such quantitation and comparison is often difficult owing to complexities in functional senescence data sets. Here, we discuss issues related to describing and contrasting age-related declines in function.
We parameterized functional senescence data in simple ways to generate descriptors for (1) the rate of functional decline, (2) the time to onset of functional decline and (3) total function. To illustrate how these descriptors can be used, we analyzed a hypothetical data set and one of our previously published data sets (Goddeeris et al., 2003). We conclude that no one descriptor sufficiently characterizes functional senescence. Useful distinctions between functional senescence in different cohorts can be made, however, when multiple descriptors are used in an integrated fashion.