Cognitive Longitudinal Predictors of Older Adults’ Self-Reported IADL Function:

A key concept in the gerontological literature is the instrumental activities of daily living (IADL). IADL, as originally delineated by Lawton & Brody (1969) include everyday tasks such as food preparation, medication use, transportation, and financial management (Depp & Jeste, 2009; Willis, 1996) and are most commonly assessed with self- and/or proxy-report measures. Older adults’ IADL function is of substantial interest given the prominent role of functional IADL independence in “successful” aging (Depp & Jeste, 2009). Furthermore, impairment in IADL has been associated with adverse outcomes such as dementia (Barberger-Gateau, Fabrigoule, Helmer, Rouch, Dartigues, 1999; Barberger-Gateau, Fabrigoule, Rouch, Letenneur, & Dartigues 1999; Peres et al., 2008), reduced psychological well-being (Lawton, 1987; Willis, 1991), greater health care utilization, increased rates of institutionalization (Miller & Weissert, 2000; Wolinsky, et al., 1983, 2007; Wolinsky, Callahan, Fitzgerald, & Johnson, 1993) and higher mortality (Ferrucci, et al., 1991; Miller & Weissert, 2000; Naeim, Keeler, & Reuben, 2007; Wolinsky et al., 1993, 2007). IADL functioning in daily life has many components, including physical, emotional, and cognitive (Willis, 1996) that interact to affect the individual over time (Verbrugge & Jette, 1994). Thus, any explanatory model with IADL as an outcome would ideally take into account these many factors. The present study focused particularly on cognitive predictors of self-reported IADL function in late life. Among studies examining cognitive predictors of IADL function, most have focused on the role of “basic” cognitive abilities (i.e., psychometrically assessed neuropsychological and experimental measures). Areas of basic cognition assessed have included aspects of memory, executive function, reasoning, and processing speed, all of which are known to decline with increasing age (Grady & Craik, 2000; Lindenberger & Ghisletta, 2009; MacDonald, Hultsch, & Dixon, 2011; Royall, Palmer, Chiodo, & Polk, 2005b; Schaie, 1994). Across studies, measures, and populations of older adults assessed, cross-sectional studies have most frequently reported a significant moderate (.48 to .61) relationship between basic cognitive abilities and IADL function (e.g., Bennett et al., 2006; Farmer & Eakman, 1995; Jefferson, Paul, Ozonoff, & Cohen, 2006; Tan, Hultsch, & Strauss, 2009). Longitudinal studies have reported moderate to large relationships (r = −.57 to −.72), with changes in IADL function related to changes in memory and executive function (e.g., Tomaszewski Farias et al., 2009; however see Tucker-Drob, 2011). This is consistent with the idea that IADL, such as meal preparation and financial management, might rely on traditionally assessed cognitive skills, such as memory. Psychometric measures of cognitive and intellectual ability are generally designed to be context-free measures of performance under optimal conditions. Responding to critiques regarding the ecological validity of such measures (e.g., Wagner & Sternberg, 1986; Chaytor & Schmitter-Edgecombe, 2003), investigators have developed measures of “everyday cognition” (Poon, Rubin, & Wilson, 1989). These measures are administered in similar fashion to those of basic cognition (i.e., paper and pencil), are novel in content, and have only one correct response per item (Allaire & Marsiske, 2002). As such, these measures are sensitive to a wide range of individual differences in performance. Everyday cognitive measures utilize stimuli from everyday life, such as nutrition labels, resemble familiar and relevant everyday IADL challenges, and encourage examinees to incorporate past experience and accumulated knowledge (Salthouse, 1990). Furthermore, everyday cognitive measures are distinct from performance-based assessments of IADL, which are commonly administered in the elder’s home by occupational therapists, have a significant physical functioning focus, and are typically assessed on a pass-fail level (e.g., Occupational Therapy Assessment of Performance and Support, see Cahn-Weiner et al., 2000). Everyday cognitive abilities are conceptualized as “hierarchical” in that they rely on basic cognitive abilities, in addition to domain specific knowledge (Marsiske & Margrett, 2006). For example, an everyday cognitive assessment might require examinees to look up a phone number in the phone book, for which they employ memory and processing speed skills, coupled with domain specific knowledge gained from prior experience using a phone book. Given their presumed closer proximity to “real world” cognition, everyday cognitive measures ought to be better predictors of functioning than basic, context-free measures of intelligence and problem solving. In support of the idea that everyday and basic cognition are related, there is evidence that everyday cognitive tasks share 50–80% of their variance with basic cognitive tasks (e.g., Allaire & Marsiske, 1999; Burton, Strauss, Hultsch, Hunter, 2006; Diehl, Willis, & Schaie, 1995; Marsiske & Margrett, 2006; Thornton, Deria, Gelb, Shapiro, Hill, 2007; Weatherbee & Allaire, 2008; Wood et al., 2005). Longitudinally, Willis, Jay, Diehl, & Marsiske (1992) found that fluid reasoning was a significant predictor of everyday cognitive skills 7 years post-baseline assessment, accounting for 52% of the variance. Two previous papers from the ACTIVE study (Gross, Rebok, Unverzagt, Willis, & Brandt, 2011; Tucker-Drob, 2011) have reported that baseline basic abilities predict level (Covariate adjusted R2 = .009 to .139) and trajectory (Covariate adjusted R2 = .013 to .051) of everyday cognition (Gross et al., 2011) as well as significant associations between trajectories of change in basic and everyday cognitive skills (rs .31 to .94; Tucker-Drob, 2011). In addition, consistent with the view that everyday cognition represents the cognitive component of IADL function, several studies have reported associations in the moderate range (r =/0.36–0.69/) between everyday cognition and self-reported IADL (e.g., Allaire & Marsiske, 2002; Diehl et al., 1995; Tan et al., 2009; Willis et al., 1998). Drawing on these previous findings, the current study examined the extent to which everyday cognition predicts self-reported IADL over time, above and beyond traditionally assessed basic cognitive abilities. Innovations of the current study include the examination of the way in which basic and everyday cognitive skills and self-reported IADL “travel together” as older adults move, on average, from young-old to old-old age. These relationships were examined in the context of an extensively-specified model with multiple predictors of attrition, re-sampling, self-reported physical health, mood, and multiple basic cognitive abilities, consistent with the conceptualization of IADL skills as contextualized and multidimensional. This model, in effect, represents a strict test of the time-varying relationship between everyday cognition and self-reported IADL. Furthermore, the everyday cognition variable examined is unique in being comprised of three measures, resulting in a multidimensional construct with psychometric variance exceeding single measure designs. Everyday cognitive measures’ capacity to capture the variance of basic abilities in self-reported IADL, as well as any unique variance exceeding these skills would support the utility of everyday cognitive measures as parsimonious clinical tools for the assessment of older adults’ IADL competence, as well as a potential endpoint for intervention efforts.