Lesa Hoffman

Persons as Contexts: Evaluating Between-Person and Within-Person Effects in Longitudinal Analysis

Relationships among multiple variables over time are of interest in many developmental areas and are frequently examined using time-varying predictors in multilevel models. Yet an incomplete specification of time-varying predictors will usually result in biased model effects. Specifically, the impact of constant, between-person sources of variation must be differentiated from the impact of time-specific, within-person sources of variation - that is, persons should be modeled as contexts. The current didactic article expands upon previous work to address why and how to model persons as contexts in longitudinal analysis. An electronic appendix of syntax for estimating these models is also provided.

Multilevel models for the experimental psychologist: Foundations and illustrative examples

Although common in the educational and developmental areas, multilevel models are not often utilized in the analysis of data from experimental designs. This article illustrates how multilevel models can be useful with two examples from experimental designs with repeated measurements not involving time. One example demonstrates how to properly examine independent variables for experimental stimuli or individuals that are categorical, continuous, or semicontinuous in the presence of missing data. The second example demonstrates how response times and error rates can be modeled simultaneously within a multivariate model in order to examine speed—accuracy trade-offs at the experimental-condition and individual levels, as well as to examine differences in the magnitude of effects across outcomes. SPSS and SAS syntax for the examples are available electronically.

Understanding verbal fluency in healthy aging, Alzheimer’s disease, and Parkinson’s disease

OBJECTIVE Verbal fluency measures are frequently part of batteries designed to assess executive function (EF), but are also used to assess semantic processing ability or word knowledge. The goal of the present study was to identify the cognitive components underlying fluency performance. METHOD Healthy young and older adults, adults with Parkinsons disease, and adults with Alzheimers disease performed letter, category, and action fluency tests. Performance was assessed in terms of number of items generated, clustering, and the time course of output. A series of neuropsychological assessments were also administered to index verbal ability, working memory, EF, and processing speed as correlates of fluency performance. RESULTS Findings indicated that regardless of the particular performance measure, young adults performed the best and adults with Alzheimers disease performed most poorly, with healthy older adults and adults with Parkinsons disease performing at intermediate levels. The exception was the action fluency task, where adults with Parkinsons disease performed most poorly. The time course of fluency performance was characterized in terms of slope and intercept parameters and related to neuropsychological constructs. Speed of processing was found to be the best predictor of performance, rather than the efficiency of EF or semantic knowledge. CONCLUSIONS Together, these findings demonstrate that the pattern of fluency performance looks generally the same regardless of how performance is measured. In addition, the primary role of processing speed in performance suggests that the use of fluency tasks as measures of EF or verbal ability warrants reexamination.

Multilevel Models for Examining Individual Differences in Within-Person Variation and Covariation over Time.

Heterogeneity of variance may be more than a statistical nuisance—it may be of direct interest as a result of individual differences. In studies of short-term fluctuation, individual differences may relate to the magnitude of within-person variation as well as to level of an outcome or its covariation with other processes. Although models for heterogeneous variances have been utilized in group contexts (i.e., dispersion models), they are not usually applied in examinations of intraindividual variation. This work illustrates how an extension of the multilevel model for heterogeneous variances can be used to examine individual differences in level, between- and within-person covariation, and magnitude of within-person variation of daily positive and negative mood in persons with dementia.

Examining the influence of task set on eye movements and fixations.

The purpose of the present study was to examine the influence of task set on the spatial and temporal characteristics of eye movements during scene perception. In previous work, when strong control was exerted over the viewing task via specification of a target object (as in visual search), task set biased spatial, rather than temporal, parameters of eye movements. Here, we find that more participant-directed tasks (in which the task establishes general goals of viewing rather than specific objects to fixate) affect not only spatial (e.g., saccade amplitude) but also temporal parameters (e.g., fixation duration). Further, task set influenced the rate of change in fixation duration over the course of viewing but not saccade amplitude, suggesting independent mechanisms for control of these parameters.

On the use of multilevel modeling as an alternative to items analysis in psycholinguistic research

The use of multilevel modeling is presented as an alternative to separate item and subject ANOVAs (F1 ×F2) in psycholinguistic research. Multilevel modeling is commonly utilized to model variability arising from the nesting of lower level observations within higher level units (e.g., students within schools, repeated measures within individuals). However, multilevel models can also be used when two random factors are crossed at the same level, rather than nested. The current work illustrates the use of the multilevel model for crossed random effects within the context of a psycholinguistic experimental study, in which both subjects and items are modeled as random effects within the same analysis, thus avoiding some of the problems plaguing current approaches.

The Role of Visual Attention in Predicting Driving Impairment in Older Adults

This study evaluated the role of visual attention (as measured by the DriverScan change detection task and the Useful Field of View Test [UFOV]) in the prediction of driving impairment in 155 adults between the ages of 63 and 87. In contrast to previous research, participants were not oversampled for visual impairment or history of automobile accidents. Although a history of automobile accidents within the past 3 years could not be predicted using any variable, driving performance in a low-fidelity simulator could be significantly predicted by performance in the change detection task and by the divided and selection attention subtests of the UFOV in structural equation models. The sensitivity and specificity of each measure in identifying at-risk drivers were also evaluated with receiver operating characteristic curves.

What Matters, and What Matters Most, for Change in Life Satisfaction in the Oldest-Old? A Study Over 6 Years Among Individuals 80+

Objectives: The study investigates whether markers of life satisfaction identified in a cross-sectional study–quality of social network, self-rated health, depressive symptoms, locus of control and widowhood, in addition to financial satisfaction and the personality traits of extraversion and neuroticism–predict change in life satisfaction (LSI-Z) across four measurement occasions during a 6-year period in individuals aged 80+. Method: Data were drawn from the Swedish OCTO-Twin-study of individuals aged 80 and older. Results: Growth curve analysis showed a relatively consistent significant linear decline in life satisfaction, but certain markers predicted change in life satisfaction. The loss of spouse, in particular in men, and higher levels of depressive symptoms were related to lower levels of life satisfaction over time. Conclusion: The results from the study question the notion of a life-long stability of life satisfaction.

Evaluating Convergence of Within-Person Change and Between-Person Age Differences in Age-Heterogeneous Longitudinal Studies.

The distinction of between-person age differences from within-person age changes is necessary for understanding aging-related change processes. Although longitudinal studies are required to address issues relating to within-person change, most studies begin using age-heterogeneous samples and conclude using survival-heterogeneous samples. Given the numerous potential confounds associated with age-heterogeneous samples, careful treatment of between-person age differences is essential to obtain the correct inferences regarding within-person age change. The authors demonstrate how failure to differentiate between-person age effects (and by extension, of survival age or other effects producing sample heterogeneity) will lead to uninterpretable inferences regarding within-person change. The authors recommend that convergence of age differences and age changes be formally evaluated whenever possible.

Daily negative mood affects fasting glucose in type 2 diabetes.

OBJECTIVE To examine the relationship between mood and blood glucose in a 21-day daily diary study. DESIGN During a home visit, information was gathered from 206 persons with Type 2 diabetes regarding demographics, disease characteristics and treatment, and depressive symptoms. They had blood drawn at a laboratory, yielding HbA1C. The participants were then telephoned each evening for 21 days and were asked about their positive and negative mood during the past 24 hours. They also tested their blood glucose upon rising in the morning. MAIN OUTCOME MEASURES The main outcomes measures were positive and negative affect and fasting glucose. RESULTS Multilevel analyses revealed a relationship between negative affect on one day and morning glucose on the next day. There was no such relationship between positive affect and glucose, nor was there a comparable effect of glucose on one day and either positive or negative affect on the next day. CONCLUSION The observed relationship between mood and blood glucose appears to be because of negative affect, not positive, with no evidence of a lagged effect of glucose on mood.