Intraindividual Variability Across the Life Span

Intraindividual variability (IIV) is the fluctuation of repeated measurements taken within an individual at closely spaced intervals over time. It is a reflection of short-term changes that may be more rapid, and usually more reversible, than developmental change that unfolds over a larger timescale of years or decades. As a feature of longitudinal data collected on micro timescales (e.g., seconds, minutes, days, or weeks), IIV can describe people, contexts, or general processes characterizing human development. In contrast to approaches that pool information across individuals and assess interindividual variability in a population (i.e., between-person variability), IIV is the focus of person-centered studies addressing how and when individuals change over time (i.e., within-person variability). Such quantitative person-centered approaches were pioneered in the middle of the 20th century ...