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    ABSTRACT: This article considers the problem of examining time-varying causal effect moderation using observational, longitudinal data in which treatment, candidate moderators, and possible confounders are time varying. The structural nested mean model (SNMM) is used to specify the moderated time-varying causal effects of interest in a conditional mean model for a continuous response given time-varying treatments and moderators. We present an easy-to-use estimator of the SNMM that combines an existing regression-with-residuals (RR) approach with an inverse-probability-of-treatment weighting (IPTW) strategy. The RR approach has been shown to identify the moderated time-varying causal effects if the time-varying moderators are also the sole time-varying confounders. The proposed IPTW+RR approach provides estimators of the moderated time-varying causal effects in the SNMM in the presence of an additional, auxiliary set of known and measured time-varying confounders. We use a small simulation experiment to compare IPTW+RR versus the traditional regression approach and to compare small and large sample properties of asymptotic versus bootstrap estimators of the standard errors for the IPTW+RR approach. This article clarifies the distinction between time-varying moderators and time-varying confounders. We illustrate the methodology in a case study to assess if time-varying substance use moderates treatment effects on future substance use. Copyright © 2013 John Wiley & Sons, Ltd.
    Statistics in Medicine 09/2014; 33(20). DOI:10.1002/sim.5892
  • Nicotine & Tobacco Research 12/2013; DOI:10.1093/ntr/ntt197
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    ABSTRACT: The Army Study to Assess Risk and Resilience in Servicemembers (Army STARRS) is a multi-component epidemiological and neurobiological study of unprecedented size and complexity designed to generate actionable evidence-based recommendations to reduce US Army suicides and increase basic knowledge about determinants of suicidality by carrying out coordinated component studies. A number of major logistical challenges were faced in implementing these studies. The current report presents an overview of the approaches taken to meet these challenges, with a special focus on the field procedures used to implement the component studies. As detailed in the paper, these challenges were addressed at the onset of the initiative by establishing an Executive Committee, a Data Coordination Center (the Survey Research Center [SRC] at the University of Michigan), and study-specific design and analysis teams that worked with staff on instrumentation and field procedures. SRC staff, in turn, worked with the Office of the Deputy Under Secretary of the Army (ODUSA) and local Army Points of Contact (POCs) to address logistical issues and facilitate data collection. These structures, coupled with careful fieldworker training, supervision, and piloting, contributed to the major Army STARRS data collection efforts having higher response rates than previous large-scale studies of comparable military samples. Copyright © 2013 John Wiley & Sons, Ltd.
    International Journal of Methods in Psychiatric Research 12/2013; DOI:10.1002/mpr.1400
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    ABSTRACT: ABSTRACT Background: Studies of gender differences in the association between socioeconomic status (SES) and cardiovascular risk factors have produced mixed findings. The purpose of this research was to examine whether the association between SES and cardiovascular risk factors differed between older men and women. Methods: Using data on physical measures and biomarkers from the 2006 Health and Retirement Study (N=2,502 men; N=3,474 women), linear regression models were used to estimate the association between SES and seven cardiovascular risk factors. Interactions between gender and SES were tested. Results: For all seven risks assessed, we observed significant associations of selected SES factors to cardiovascular risk for men and/or women. In all of these cases, lower SES was associated with higher cardiovascular risk. However, for six of the factors, we also observed gender differences in the association between SES and cardiovascular risk, such that lower SES was associated with higher cardiovascular risk for women but not for men. These findings suggest that the association between SES and cardiovascular risk is more pronounced for women than for men. Implications: Implementing interventions to reduce cardiovascular risk factors, particularly among older women with lower SES, might over time reduce cardiovascular disease in women and improve quality of life.
    Women & Health 11/2013; DOI:10.1080/03630242.2013.858098
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    ABSTRACT: To examine short-term consequences associated with consuming alcohol and energy drinks compared with consuming alcohol without energy drinks. A longitudinal measurement-burst design (14-day bursts of daily surveys in four consecutive college semesters) captured both within-person variation across occasions and between-person differences across individuals. The analytic sample of late adolescent alcohol users included 4,203 days with alcohol use across up to four semesters per person from 508 college students. Adding energy drink use to a given day with alcohol use was associated with an increase in number of alcoholic drinks, a trend toward more hours spent drinking, elevated estimated blood alcohol content (eBAC), a greater likelihood of subjective intoxication, and more negative consequences of drinking that day. After controlling for eBAC, energy drink use no longer predicted subjective intoxication but was still associated with a greater number of negative consequences. The consumption of energy drinks may lead to increases in alcohol consumption and, after controlling for eBAC, negative consequences. Use of energy drinks plus alcohol represents an emerging threat to public health.
    Journal of Adolescent Health 11/2013; DOI:10.1016/j.jadohealth.2013.09.013
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    ABSTRACT: We agree with Kawada that the ideal data set for our study would include a confounder-free experiment that asks the self-rated health (SRH) question in different contexts (or order) and follows study participants over time to assess subsequent morbidity and mortality. This data set does not exist. As an approximation with minimal methodological noncomparability, we used the National Health Interview Survey linked with the National Death Index and the Health and Retirement Study (HRS) to examine SRH context effects on health outcome predictions. (Am J Public Health. Published online ahead of print November 14, 2013: e1-e2. doi:10.2105/AJPH.2013.301712).
    American Journal of Public Health 11/2013; DOI:10.2105/AJPH.2013.301712
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    ABSTRACT: This paper explores how a reference point affects individual preferences. While reference-dependence is extensively studied, very little is known regarding the impact of reference points on individual choice behavior when the reference point itself is abandoned. We show that reference-dependence is not limited to the endowment effect and status quo bias — choices appear to be influenced by reference points, even when agents do not stick to the reference point itself (Reference Effect). In a laboratory experiment, we find that approximately half of all subjects exhibit some reference-dependence. Moreover, we show that the leading models of reference-dependence make contradictory predictions regarding the reference effect. We find that some of these reference-dependent models are capable of explaining most of our data. Understanding the impact of reference points on individual's choice has important policy implications including how default options are determined such as with 401(k) retirement plans.
    Games and Economic Behavior 11/2013; 82. DOI:10.1016/j.geb.2013.07.009
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    ABSTRACT: Purpose of the Study: Social relations are a key aspect of aging and the life course. In this paper, we trace the scientific origins of the study of social relations, focusing in particular on research grounded in the convoy model. We first briefly review and critique influential historical studies to illustrate how the scientific study of social relations developed. Next, we highlight early and current findings grounded in the convoy model that have provided key insights into theory, method, policy, and practice in the study of aging. Early social relations research, while influential, lacked the combined approach of theoretical grounding and methodological rigor. Nevertheless, previous research findings, especially from anthropology, suggested the importance of social relations in the achievement of positive outcomes. Considering both life span and life course perspectives and grounded in a multidisciplinary perspective, the convoy model was developed to unify and consolidate scattered evidence while at the same time directing future empirical and applied research. Early findings are summarized, current evidence presented, and future directions projected. The convoy model has provided a useful framework in the study of aging, especially for understanding predictors and consequences of social relations across the life course.
    The Gerontologist 10/2013; DOI:10.1093/geront/gnt118
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    ABSTRACT: Purpose of the Study: Comprehensive measures of disability accommodations have been lacking in national health and aging studies. This article introduces measures of accommodations developed for the National Health and Aging Trends Study, evaluates their reliability, and explores the validity and reliability of hierarchical classification schemes derived from these measures. We examined test-retest reliability for questions about assistive device use, doing activities less often, and getting help from another person with both percentage agreement and kappa (N = 111). Summary measures across activities and several hierarchical classification schemes (e.g., no accommodation, devices/activity reductions only, help) were developed. For the latter, we also evaluated validity by examining correlations with measures of capacity and demographic characteristics (N = 326). Items about assistive device use and help in the last month were robust (most kappas 0.7-0.9). Activity reduction measures were moderately reliable (around 0.5) but still showed reasonable agreement. Reliabilities for summary measures were good for device use (0.78-0.89) and help (0.62-0.67) but lower, albeit acceptable, for activity reduction (0.53). Hierarchical classifications had acceptable reliability and levels demonstrated hierarchical properties. National Health and Aging Trends Study's self-care and mobility accommodation measures offer ample reliability to study adaptation to limitations and can be used to construct a reliable and valid hierarchy.
    The Gerontologist 09/2013; DOI:10.1093/geront/gnt104
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    ABSTRACT: Socioeconomic status and acculturation may modify the association between ethnicity and hypertension treatment before stroke. We assessed prestroke treatment of hypertension by ethnicity, education (proxy for socioeconomic status), and English proficiency (EP; proxy for acculturation) in a population-based stroke surveillance project. Among 763 patients with first-ever stroke aged ≥45 years in the Brain Attack Surveillance in Corpus Christi project from 2000 to 2006, we examined self-reported hypertension treatment at the time of the stroke by ethnicity (Mexican American [MA] versus non-Hispanic white [NHW]) in the overall sample, within education strata (<high school, high school, >high school), and after dichotomizing MAs by self-reported EP (limited versus proficient). Logistic regression adjusted associations for age, sex, education, diabetes mellitus, coronary artery disease, hypercholesterolemia, and health insurance. NHWs and MAs reported similar hypertension treatment (84% versus 86%; P=0.53). Hypertension treatment was 84% for NHWs and 90% for MAs (P=0.18) in <high school stratum, 87% for NHWs and 75% for MAs (P=0.07) in high school stratum, and 81% for NHWs and 78% for MAs (P=0.73) in >high school stratum (ethnicity-by-education interaction, P=0.09). Hypertension treatment was 83% for NHWs, 87% for MAs with EP (PvsNHWs=0.35), and 90% for MAs with limited EP (PvsNHWs=0.13; ethnicity-by-EP interaction, P=0.22). Hypertension treatment was lower in uninsured patients (adjusted odds ratio, 0.13; 95% confidence interval, 0.03-0.60) or those with no physician visit ≤6 months (adjusted odds ratio, 0.09; 95% confidence interval, 0.03-0.24). We found no evidence that socioeconomic status or acculturation modifies the association between ethnicity and hypertension treatment before stroke.
    Stroke 09/2013; 44(11). DOI:10.1161/STROKEAHA.113.003051
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