The pace of aging: Intrinsic time scales in demography

Abstract

BACKGROUND The pace of aging is a concept that captures the time-related aspect of aging. It formalizes the idea of a characteristic life span or intrinsic population time scale. In the rapidly developing field of comparative biodemography, measures that account for inter-species differences in life span are needed to compare how species age. OBJECTIVE We aim to provide a mathematical foundation for the concept of pace. We derive desired mathematical properties of pace measures and suggest candidates which satisfy these properties. Subsequently, we introduce the concept of pace-standardization, which reveals differences in demographic quantities that are not due to pace. Examples and consequences are discussed. CONCLUSIONS Mean life span (i.e., life expectancy from birth or from maturity) is intuitively appealing, theoretically justified, and the most appropriate measure of pace. Pace-standardization provides a serviceable method for comparative aging studies to explore differences in demographic patterns of aging across species, and it may considerably alter conclusions about the strength of aging.