Multiple Time Scale Design

Background and Development of the Method

Longitudinal (panel) designs, whereby the same sets of participants are assessed repeatedly over time, have been instrumental in providing descriptive information on human life-span development. These designs have many advantages over cross-sectional designs, which compare individuals of one age-group to individuals of one or more other age groups at one specific point in time. Cross-sectional studies are limited in their ability to reveal the trajectory and rate of human development. Longitudinal studies remedy some of these problems by tracking the same sets of participants across the course of various developmental periods, thereby allowing for the characterization of changes within the individual. Longitudinal studies can also differentiate patterns of development between individuals. For example, longitudinal methods can reveal not only how intelligence changes across the life span but also which individuals may show the most rapid increases in intelligence (e.g., those exposed to enriched environments).

Although longitudinal studies have several advantages, this research design is not without limitations. One challenge, in particular, is that researchers must determine the optimal temporal intervals between waves to properly observe and describe development. If intervals are too far apart, developmental milestones (e.g., puberty, menopause) may be missed. In contrast, if sampling occurs too frequently, study resources may be expended unnecessarily and participants may be burdened with excessive assessments. Additionally, various domains of functioning (e.g., cognitive, socioemotional, psychological, physical, neurological) may develop at different rates and in varying directions and patterns between persons, as well as within persons, at unique phases of the life span. For example, from infancy to toddlerhood, vocabulary rapidly develops, but moral development shows slower changes. Across adulthood, however, these domains show different patterns: Vocabulary continues to increase but at a slower rate, whereas moral development can change in different directions when life transitions occur. That is, religious beliefs and participation are relatively low during adolescence and young adulthood but may increase with major life transitions (e.g., becoming a parent for the first time).

Researchers have balanced the costs of collecting multiple waves of longitudinal data by assessing participants only every several years or once per decade, to cover larger portions of the (adult) life span with fewer waves of assessments. Such studies, however, may not ideally capture developmental processes that unfold over shorter intervals or that show more rapid and dynamic fluctuations in daily life (e.g., emotional states). Multiple timescale designs have been introduced to address these methodological weaknesses. These designs involve sampling intensive measurements relatively close together in time (i.e., bursts) and repeating the bursts across longer time intervals (e.g., months, years, or decades).

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