Multivariate Modeling of Age and Retest in Longitudinal Studies of Cognitive Abilities.

Abstract

Longitudinal multivariate mixed models were used to examine the correlates of change between memory and processing speed and the contribution of age and retest to such change correlates. Various age-and occasion-mixed models were fitted to 2 longitudinal data sets of adult individuals (N > 1,200). For both data sets, the results indicated that the correlation between the age slopes of memory and processing speed decreased when retest effects were included in the model. If retest effects existed in the data but were not modeled, the correlation between the age slopes was positively biased. The authors suggest that although the changes in memory and processing speed may be correlated over time, age alone does not capture such a covariation.Keywords multivariate models of change; longitudinal methodology; multivariate latent growth curves; practice effects Practice effects are one source of possible confounding effects in longitudinal studies. Individuals who repeat a test may perform better merely as a result of the influence from the previous assessment. In the context of a longitudinal study with repeated observations, the effects attributed to age might be contaminated with retest effects (Donaldson & Horn, 1992;Hertzog & Nesselroade, 2003). Several articles have illustrated this issue and the need to model separate effects for age and retest (Ferrer, Salthouse, Stewart, & Schwartz, 2004; Lövdén, Ghisletta, & Lindenberger, 2004;McArdle & Anderson, 1990; McArdle, FerrerCaja, Hamagami, & Woodcock, 2002;McArdle & Woodcock, 1997; Rabbitt, Diggle, Holland, & McInnes, 2004; Rabbitt, Diggle, Smith, Holland, & McInnes, 2001;Salthouse, Schroeder, & Ferrer, 2004;Wilson et al., 2002 NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript indicate that both age and retest should be modeled simultaneously when examining change of cognitive abilities over time. When practice effects exist as a result of repeated assessments, ignoring the retest component underestimates the negative age effects, with larger bias for stronger retest effects. In this study, we extend this work to multivariate analyses. We argue that similar bias existing in univariate studies may occur in multivariate analyses that focus on correlates of change. Such correlates of change have age and retest components, and both need to be modeled separately to identify their own contribution to the change correlation.One essential question in current research in cognitive aging is the extent to which various cognitive domains change in a parallel way. Researchers are interested in examining whether cognitive abilities covary over age or whether they change independently as a function of different underlying mechanisms (e.g., Deary, 2001). A large number of crosssectional studies have examined this question by comparing age-related variance in various cognitive abilities and then estimating the shared part of the variance (Baltes & Lindenberger, 1997;Lindenberger & Baltes, 1994;Rabbitt, 1993;Salthouse & Ferrer-Caja, 2003). In genera...

Predictors of Retest Effects in a Longitudinal Study of Cognitive Aging in a Diverse Community-Based Sample

“…These effects are well-documented in longitudinal studies of cognitive aging (Abner et al, 2012; Basso et al, 1999; Calamia et al, 2012; Collie et al, 2003; Cooper, Lacritz, Weiner, Rosenberg, & Cullum, 2004; Duff et al, 2011; Ferrer et al, 2004, 2005; Frank et al, 1996; Horton et al, 1992; Howieson et al, 2008; Ivnik et al, 1999; Jacqmin-Gadda et al, 1997; Machulda et al, 2013; Mitrushina et al, 1991; Rabbitt et al, 2001, 2004; Salthouse, 2009; Wilson, Leurgans, Boyle, & Bennett, 2011; Wilson et al, 2006; Zehnder et al, 2007). A consensus conference for clinical neuropsychology has called for research on ramifications of repeated cognitive testing (Heilbronner et al, 2010).…”

Two thirds of the age-based changes in fluid and crystallized intelligence, perceptual speed, and memory in adulthood are shared

“…At occasions 2, 3, and 4 we included a dummy variable for each cognitive task to estimate the change in performance independent of aging effects. This technique is widely applied and has proved useful in a number of independent studies (e.g., Ferrer, Salthouse, McArdle, Stewart, & Schwartz, 2005;Ghisletta & de Ribaupierre, 2005;Lövdén, Ghisletta, & Lindenberger, 2004;McArdle, Prescott, Hamagami, & Horn, 1998;Rabbitt et al, 2004). However, this coding scheme does not allow estimating random effects in retest (else the model is overparameterized).…”

Enrichment Effects on Adult Cognitive Development

“…Assessing practice effects inside a longitudinal design is in and of itself a difficult modeling exercise that requires a number of assumptions, because longitudinal designs explicitly targeting practice effects are rarely employed (see McArdle & Woodcock, 1997). Nonetheless, there is broad agreement that practice effects in longitudinal aging studies have led to underestimation of the average amount of age-related cognitive decline (Ferrer, Salthouse, McArdle, Stewart, & Schwartz, 2005;Ferrer, Salthouse, Stewart, & Schwartz, 2004;Rabbitt, Diggle, Holland, & McInness, 2004;Wilson, Beckett, et al, 2002;Wilson, Li, Bienias, & Bennett, 2006). In cognitiveenrichment research, however, the focus is on the relation of enrichment variables to individual differences in cognitive change rather than on the absolute level of change taking place.…”