Power Calculations for General Linear Multivariate Models Including Repeated Measures Applications

Recently developed methods for power analysis expand the options available for study design. We demonstrate how easily the methods can be applied by (1) reviewing their formulation and (2) describing their application in the preparation of a particular grant proposal. The focus is a complex but ubiquitous setting: repeated measures in a longitudinal study. Describing the development of the research proposal allows demonstrating the steps needed to conduct an effective power analysis. Discussion of the example also highlights issues that typically must be considered in designing a study. First, we discuss the motivation for using detailed power calculations, focusing on multivariate methods in particular. Second, we survey available methods for the general linear multivariate model (GLMM) with Gaussian errors and recommend those based on F approximations. The treatment includes coverage of the multivariate and univariate approaches to repeated measures, MANOVA, ANOVA, multivariate regression, and univariate regression. Third, we describe the design of the power analysis for the example, a longitudinal study of a child’s intellectual performance as a function of mother’s estimated verbal intelligence. Fourth, we present the results of the power calculations. Fifth, we evaluate the tradeoffs in using reduced designs and tests to simplify power calculations. Finally, we discuss the benefits and costs of power analysis in the practice of statistics. We make three recommendations

Medical Records-Based Postmarketing Safety Evaluation of Rare Events with Uncertain Status

We develop a simple statistic for comparing rates of rare adverse events between treatment groups in post-marketing safety studies where the events have uncertain status. In this setting, the statistic is asymptotically equivalent to the logrank statistic, but the limiting distribution has Poisson and binomial components instead of being Guassian. We develop two new procedures for computing critical values, a Gaussian approximation and a parametric bootstrap. Both numerical and asymptotic properties of the procedures are studied. The test procedures are demonstrated on a post-marketing safety study of the RotaTeq vaccine. This vaccine was developed to reduce the incidence of severe diarrhea in infants

Cancer Incidence Among Those Initiating Insulin Therapy With Glargine Versus Human NPH Insulin

OBJECTIVE To add to the evidence on comparative long-term effects of insulin analog glargine versus human NPH insulin on the risk for cancer. RESEARCH DESIGN AND METHODS We identified cohorts of initiators of glargine and human NPH without an insulin prescription during the prior 19 months among patients covered by the Inovalon Medical Outcomes Research for Effectiveness and Economics Registry (MORE2 Registry) between January 2003 and December 2010. Patients were required to have a second prescription of the same insulin within 180 days and to be free of cancer. We balanced cohorts on risk factors for cancer outcomes based on comorbidities, comedication, and health care use during the prior 12 months using inverse probability of treatment weighting. Incident cancer was defined as having two claims for cancer (any cancer) or the same cancer (breast, prostate, colon) within 2 months. We estimated adjusted hazard ratios (HRs) and their 95% CI using weighted Cox models censoring for stopping, switching, or augmenting insulin treatment, end of enrollment, and mortality. RESULTS More patients initiated glargine (43,306) than NPH (9,147). Initiators of glargine (NPH) were followed for 1.2 (1.1) years and 50,548 (10,011) person-years; 993 (178) developed cancer. The overall HR was 1.12 (95% CI 0.95–1.32). Results were consistent for breast cancer, prostate cancer, and colon cancer; various durations of treatment; and sensitivity analyses. CONCLUSIONS Patients initiating insulin glargine rather than NPH do not seem to be at an increased risk for cancer. While our study contributes significantly to our evidence base for long-term effects, this evidence is very limited mainly based on actual dynamics in insulin prescribing

Metformin for Weight Loss and Metabolic Control in Overweight Outpatients With Schizophrenia and Schizoaffective Disorder

The purpose of this study was to determine whether metformin promotes weight loss in overweight out-patients with chronic schizophrenia or schizoaffective disorder

A Randomized Trial Examining the Effectiveness of Switching From Olanzapine, Quetiapine, or Risperidone to Aripiprazole to Reduce Metabolic Risk: Comparison of Antipsychotics for Metabolic Problems (CAMP)

We conducted a multi-site, randomized controlled trial examining the strategy of switching from olanzapine, quetiapine, or risperidone to aripiprazole to ameliorate metabolic risk factors for cardiovascular disease

Prevalence of Hypertension, Awareness, Treatment, and Control in the Hispanic Community Health Study/Study of Latinos

The prevention and control of hypertension is an essential component for reducing the burden of cardiovascular diseases. Here we describe the prevalence of hypertension in diverse Hispanic/Latino background groups and describe the proportion who are aware of their diagnosis, receiving treatment, and having their hypertension under control

Sample Design and Cohort Selection in the Hispanic Community Health Study/Study of Latinos

The Hispanic Community Health Study (HCHS)/Study of Latinos (SOL) is a multi-center, community based cohort study of Hispanic/Latino adults in the United States. A diverse participant sample is required that is both representative of the target population and likely to remain engaged throughout follow-up. The choice of sample design, its rationale, and benefits and challenges of design decisions are described in this paper

Prevalence of Diabetes Among Hispanics/Latinos From Diverse Backgrounds: The Hispanic Community Health Study/Study of Latinos (HCHS/SOL)

OBJECTIVEWe examine differences in prevalence of diabetes and rates of awareness and control among adults from diverse Hispanic/Latino backgrounds in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL).RESEARCH DESIGN AND METHODSThe HCHS/SOL, a prospective, multicenter, population-based study, enrolled from four U.S. metropolitan areas from 2008 to 2011 16,415 18–74-year-old people of Hispanic/Latino descent. Diabetes was defined by either fasting plasma glucose, impaired glucose tolerance 2 h after a glucose load, glycosylated hemoglobin (A1C), or documented use of hypoglycemic agents (scanned medications).RESULTSDiabetes prevalence varied from 10.2% in South Americans and 13.4% in Cubans to 17.7% in Central Americans, 18.0% in Dominicans and Puerto Ricans, and 18.3% in Mexicans (P < 0.0001). Prevalence related positively to age (P < 0.0001), BMI (P < 0.0001), and years living in the U.S. (P = 0.0010) but was negatively related to education (P = 0.0005) and household income (P = 0.0043). Rate of diabetes awareness was 58.7%, adequate glycemic control (A1C <7%, 53 mmol/mol) was 48.0%, and having health insurance among those with diabetes was 52.4%.CONCLUSIONSPresent findings indicate a high prevalence of diabetes but considerable diversity as a function of Hispanic background. The low rates of diabetes awareness, diabetes control, and health insurance in conjunction with the negative associations between diabetes prevalence and both household income and education among Hispanics/Latinos in the U.S. have important implications for public health policies

Depression, anxiety, antidepressant use, and cardiovascular disease among Hispanic men and women of different national backgrounds: results from the Hispanic Community Health Study/Study of Latinos

Describe prevalence and relationships to cardiovascular morbidity of depression, anxiety and medication use among Hispanic/Latinos of different ethnic backgrounds

Design and Implementation of the Hispanic Community Health Study/Study of Latinos

The Hispanic Community Health Study (HCHS)/Study of Latinos (SOL) is a comprehensive multi-center community based cohort study of Hispanics/Latinos in the United States. Its rationale, objectives, design and implementation are described in this paper