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Intraindividual Variability in Lifespan Developmental Methodology  

Eric S. Cerino and Karen Hooker

Intraindividual variability (IIV) refers to short-term fluctuations that may be more rapid, and are often conceptualized as more reversible, than developmental change that unfolds over a longer period of time, such as years. As a feature of longitudinal data collected on micro timescales (i.e., 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). Developmental psychologists interested in change and how and when it occurs, have devised research methods designed to examine intraindividual change (IIC) and interindividual differences in IIC. Dispersion, variability, inconsistency, time-structured IIV, and net IIV are distinct operationalizations of IIV that, depending on the number of measures, occasions, and time of measurement, reflect unique information about IIV in lifespan developmental domains of interest. Microlongitudinal and measurement-burst designs are two methodological approaches with intensive repeated measurement that provide a means by which various operationalizations of IIV can be accurately observed over an appropriate temporal frame to garner clearer understanding of the dynamic phenomenon under investigation. When methodological approaches are theoretically informed and the temporal frame and number of assessments align with the dynamic lifespan developmental phenomenon of interest, researchers gain greater precision in their observations of within-person variability and the extent to which these meaningful short-term fluctuations influence important domains of health and well-being. With technological advancements fueling enhanced methodologies and analytic approaches, IIV research will continue to be at the vanguard of pioneering designs for elucidating developmental change at the individual level and scaling it up to generalize to populations of interest.


William Stern (1871–1938), Eclipsed Star of Early 20th-Century Psychology  

James Lamiell

In the literature of mainstream scientific psychology, German scholar William Stern has been known primarily (if at all) as the inventor of the intelligence quotient (IQ). In fact, however, Stern’s contributions to psychology were much greater and more consequential than this. In this all-inclusive article, I have sought to provide readers with a fuller appreciation for the breadth and depth of Stern’s work, and, in particular, for that comprehensive system of thought that he elaborated under the name “critical personalism.” Drawing frequently on translated quotations from Stern’s published works, and on his personal correspondence with the Freiburg philosopher Jonas Cohn, I have endeavored to show how Stern was much more than “the IQ guy.” During the first 20 years of his academic career, spent at the University of Breslau in what is now the Polish city of Wroclaw, Stern founded that sub-discipline of psychology that would be concentrated on the study of individual differences in various aspects of human psychological functioning. He also made major contributions to that sub-discipline referred to at the time as “child” psychology, and laid the foundations for a comprehensive system of thought that he would name “critical personalism.” After relocating to Hamburg in 1916, Stern continued his scholarly efforts in these domains, taught courses both in psychology and in philosophy at the university that opened its doors there in 1919, and played major administrative roles there in the institutional homes of both disciplines until forced to flee Nazi Germany in 1934. The present chapter highlights ways in which, over the course of his scholarly career, Stern boldly opposed certain trends within mainstream thinking that were ascendant during his time.