title: Intraindividual variability, change, and aging: conceptual and analytical issues.
abstract: BACKGROUND
  Developmental researchers use a variety of research designs to examine aging-related changes. Most longitudinal studies of aging are based on research designs that feature successive, widely spaced, assessments to estimate changes in cognitive performance. Such designs assume that short-term variations in cognitive performance are small relative to long-term changes or have modeled such phenomena as nuisance parameters.
  
  
  OBJECTIVE
  There is now sufficient empirical evidence to establish intraindividual cognitive variability as a systematic source of individual differences and of important predictive value for aging-relevant outcomes.
  
  
  METHODS
  After an overview of types of change, potential underlying processes, and adequate analytic designs, we discuss consequences for lifespan aging research.
  
  
  RESULTS
  We emphasize that interpretations of both cross-sectional and longitudinal results need to consider and specify theoretical assumptions about short-term and long-term changes.
  
  
  CONCLUSIONS
  Above and beyond the analysis of long-term mean changes, short- term changes are an important aspect of aging-related change, and their analysis may help to explain psychological processes of adaptation.
authors.affiliation: Department of Gerontopsychology, Institute of Psychology, Zurich, Switzerland. m.martin@psychologie.unizh.ch
authors.forename: Mike
authors.initials: M
authors.lastname: Martin
authors.forename: Scott M
authors.initials: SM
authors.lastname: Hofer
mesh_terms: D000375:Aging / Q000502:physiology*; D003071:Cognition / Q000502:physiology*; D015988:Cohort Effect; D006801:Humans; D007206:Individuality; D008960:Models, Psychological; D012107:Research Design; D015983:Selection Bias