Babette A Brumback

University of Florida, Gainesville, Florida, United States

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Publications (39)86.97 Total impact

  • Babette A Brumback, Zhuangyu Cai, Amy B Dailey
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    ABSTRACT: Reasons for health disparities may include neighborhood-level factors, such as availability of health services, social norms, and environmental determinants, as well as individual-level factors. Investigating health inequalities using nationally or locally representative data often requires an approach that can accommodate a complex sampling design, in which individuals have unequal probabilities of selection into the study. The goal of the present article is to review and compare methods of estimating or accounting for neighborhood influences with complex survey data. We considered 3 types of methods, each generalized for use with complex survey data: ordinary regression, conditional likelihood regression, and generalized linear mixed-model regression. The relative strengths and weaknesses of each method differ from one study to another; we provide an overview of the advantages and disadvantages of each method theoretically, in terms of the nature of the estimable associations and the plausibility of the assumptions required for validity, and also practically, via a simulation study and 2 epidemiologic data analyses. The first analysis addresses determinants of repeat mammography screening use using data from the 2005 National Health Interview Survey. The second analysis addresses disparities in preventive oral health care using data from the 2008 Florida Behavioral Risk Factor Surveillance System Survey.
    American journal of epidemiology 04/2014; · 5.59 Impact Factor
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    ABSTRACT: Much attention has been paid to estimating the causal effect of adherence to a randomized protocol using instrumental variables to adjust for unmeasured confounding. Researchers tend to use the instrumental variable within one of the three main frameworks: regression with an endogenous variable, principal stratification, or structural-nested modeling. We found in our literature review that even in simple settings, causal interpretations of analyses with endogenous regressors can be ambiguous or rely on a strong assumption that can be difficult to interpret. Principal stratification and structural-nested modeling are alternative frameworks that render unambiguous causal interpretations based on assumptions that are, arguably, easier to interpret. Our interest stems from a wish to estimate the effect of cluster-level adherence on individual-level binary outcomes with a three-armed cluster-randomized trial and polytomous adherence. Principal stratification approaches to this problem are quite challenging because of the sheer number of principal strata involved. Therefore, we developed a structural-nested modeling approach and, in the process, extended the methodology to accommodate cluster-randomized trials with unequal probability of selecting individuals. Furthermore, we developed a method to implement the approach with relatively simple programming. The approach works quite well, but when the structural-nested model does not fit the data, there is no solution to the estimating equation. We investigate the performance of the approach using simulated data, and we also use the approach to estimate the effect on pupil absence of school-level adherence to a randomized water, sanitation, and hygiene intervention in western Kenya. Copyright © 2013 John Wiley & Sons, Ltd.
    Statistics in Medicine 11/2013; · 2.04 Impact Factor
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    ABSTRACT: SUMMARY The impact of improved water, sanitation, and hygiene (WASH) access on mitigating illness is well documented, although impact of school-based WASH on school-aged children has not been rigorously explored. We conducted a cluster-randomized trial in Nyanza Province, Kenya to assess the impact of a school-based WASH intervention on diarrhoeal disease in primary-school pupils. Two study populations were used: schools with a nearby dry season water source and those without. Pupils attending 'water-available' schools that received hygiene promotion and water treatment (HP&WT) and sanitation improvements showed no difference in period prevalence or duration of illness compared to pupils attending control schools. Those pupils in schools that received only the HP&WT showed similar results. Pupils in 'water-scarce' schools that received a water-supply improvement, HP&WT and sanitation showed a reduction in diarrhoea incidence and days of illness. Our study revealed mixed results on the impact of improvements to school WASH improvements on pupil diarrhoea.
    Epidemiology and Infection 05/2013; · 2.87 Impact Factor
  • Zhulin He, Babette A. Brumback
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    ABSTRACT: Motivated by an application with complex survey data, we show that for logistic regression with a simple matched-pairs design, infinitely replicating observations and maximizing the conditional likelihood results in an estimator exactly identical to the unconditional maximum likelihood estimator based on the original sample, which is inconsistent. Therefore, applying conditional likelihood methods to a pseudosample with observations replicated a large number of times can lead to an inconsistent estimator; this casts doubt on one possible approach to conditional logistic regression with complex survey data. We speculate that for more general designs, an asymptotic equivalence holds.
    Communication in Statistics- Theory and Methods 01/2013; 42(18). · 0.30 Impact Factor
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    ABSTRACT: The CHIRP Study is a two-arm, pilot randomized controlled trial assessing the effectiveness of a behavioral family weight management intervention in an important and at-risk population, overweight young children, 3 to 6years of age, and their parents from underserved rural counties. Participants will include 96 parent-child dyads living in rural counties in north central Florida. Families will be randomized to one of two conditions: (a) Behavioral Family Based Intervention or (b) a Waitlist Control. Child and parent participants will be assessed at baseline (month 0), post-treatment (month 4), and follow-up (month 10). Assessments and intervention sessions will be held at the Cooperative Extension office in each participating rural county. The primary outcome measure is change in child body mass index (BMI) z-score. Additional key outcome measures include child dietary intake, physical activity, and parent BMI. This study is unique because (1) it is one of the few randomized controlled trails examining a behavioral family intervention to address healthy habits and improved weight status in young overweight and obese children, (2) addresses health promotion in rural settings, (3) examines intervention delivery in real world community settings through the Cooperative Extension Service offices. If successful, this research has potential implications for medically underserved rural communities and preventative health services for young children and their families.
    Contemporary clinical trials 11/2012; · 1.51 Impact Factor
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    ABSTRACT: In order to adjust individual-level covariate effects for confounding due to unmeasured neighborhood characteristics, we have recently developed conditional pseudolikelihood methods to estimate the parameters of a proportional odds model for clustered ordinal outcomes with complex survey data. The methods require sampling design joint probabilities for each within-neighborhood pair. In the present article, we develop a similar methodology for a baseline category logit model for clustered multinomial outcomes and for a loglinear model for clustered count outcomes. All of the estimators and asymptotic sampling distributions we present can be conveniently computed using standard logistic regression software for complex survey data, such as sas proc surveylogistic. We demonstrate validity of the methods theoretically and also empirically by using simulations. We apply the new method for clustered multinomial outcomes to data from the 2008 Florida Behavioral Risk Factor Surveillance System survey in order to investigate disparities in frequency of dental cleaning both unadjusted and adjusted for confounding by neighborhood. Copyright © 2012 John Wiley & Sons, Ltd.
    Statistics in Medicine 09/2012; · 2.04 Impact Factor
  • Babette A Brumback, Hao W Zheng, Amy B Dailey
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    ABSTRACT: When investigating health disparities, it can be of interest to explore whether adjustment for socioeconomic factors at the neighborhood level can account for, or even reverse, an unadjusted difference. Recently, we proposed new methods to adjust the effect of an individual-level covariate for confounding by unmeasured neighborhood-level covariates using complex survey data and a generalization of conditional likelihood methods. Generalized linear mixed models (GLMMs) are a popular alternative to conditional likelihood methods in many circumstances. Therefore, in the present article, we propose and investigate a new adaptation of GLMMs for complex survey data that achieves the same goal of adjusting for confounding by unmeasured neighborhood-level covariates. With the new GLMM approach, one must correctly model the expectation of the unmeasured neighborhood-level effect as a function of the individual-level covariates. We demonstrate using simulations that even if that model is correct, census data on the individual-level covariates are sometimes required for consistent estimation of the effect of the individual-level covariate. We apply the new methods to investigate disparities in recency of dental cleaning, treated as an ordinal outcome, using data from the 2008 Florida Behavioral Risk Factor Surveillance System (BRFSS) survey. We operationalize neighborhood as zip code and merge the BRFSS data with census data on ZIP Code Tabulated Areas to incorporate census data on the individual-level covariates. We compare the new results to our previous analysis, which used conditional likelihood methods. We find that the results are qualitatively similar. Copyright © 2012 John Wiley & Sons, Ltd.
    Statistics in Medicine 09/2012; · 2.04 Impact Factor
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    ABSTRACT: INTRODUCTION: Due to time-dependent confounding by blood pressure and differential loss to follow-up, it is difficult to estimate the effectiveness of aggressive versus conventional antihypertensive combination therapies in non-randomized comparisons. METHODS: We utilized data from 22,576 hypertensive coronary artery disease patients, prospectively enrolled in the INternational VErapamil-Trandolapril STudy (INVEST). Our post-hoc analyses did not consider the randomized treatment strategies, but instead defined exposure time-dependently as aggressive treatment ([greater than or equal to]3 concomitantly used antihypertensive medications) versus conventional treatment ([less than or equal to]2 concomitantly used antihypertensive medications). Study outcome was defined as time to first serious cardiovascular event (non-fatal myocardial infarction, non-fatal stroke, or all-cause death). We compared hazard ratio (HR) estimates for aggressive vs. conventional treatment from a Marginal Structural Cox Model (MSCM) to estimates from a standard Cox model. Both models included exposure to antihypertensive treatment at each follow-up visit, demographics, and baseline cardiovascular risk factors, including blood pressure. The MSCM further adjusted for systolic blood pressure at each follow-up visit, through inverse probability of treatment weights. RESULTS: 2,269 (10.1%) patients experienced a cardiovascular event over a total follow-up of 60,939 person-years. The HR for aggressive treatment estimated by the standard Cox model was 0.96 (95% confidence interval 0.87-1.07). The equivalent MSCM, which was able to account for changes in systolic blood pressure during follow-up, estimated a HR of 0.81 (95% CI 0.71-0.92). CONCLUSIONS: Using a MSCM, aggressive treatment was associated with a lower risk for serious cardiovascular outcomes compared to conventional treatment. In contrast, a standard Cox model estimated similar risks for aggressive and conventional treatments.
    BMC Medical Research Methodology 08/2012; 12(1):119. · 2.21 Impact Factor
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    ABSTRACT: Model-based standardization enables adjustment for confounding of a population-averaged exposure effect on an outcome. It requires either a model for the probability of the exposure conditional on the confounders (an exposure model) or a model for the expectation of the outcome conditional on the exposure and the confounders (an outcome model). The methodology can also be applied to estimate averaged exposure effects within categories of an effect modifier and to test whether these effects differ or not. Recently, we extended that methodology for use with complex survey data, to estimate the effects of disability status on cost barriers to health care within three age categories and to test for differences. We applied the methodology to data from the 2007 Florida Behavioral Risk Factor Surveillance System Survey (BRFSS). The exposure modeling and outcome modeling approaches yielded two contrasting sets of results. In the present paper, we develop and apply to the BRFSS example two doubly robust approaches to testing and estimating effect modification with complex survey data; these approaches require that only one of these two models be correctly specified. Furthermore, assuming that at least one of the models is correctly specified, we can use the doubly robust approaches to develop and apply goodness-of-fit tests for the exposure and outcome models. We compare the exposure modeling, outcome modeling, and doubly robust approaches in terms of a simulation study and the BRFSS example. Copyright © 2012 John Wiley & Sons, Ltd.
    Statistics in Medicine 07/2012; · 2.04 Impact Factor
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    ABSTRACT: To examine the concept of leukoaraiosis thresholds on working memory, visuoconstruction, memory, and language in dementia. A consecutive series of 83 individuals with insidious onset/progressive dementia clinically diagnosed with Alzheimer disease (AD) or small vessel vascular dementia (VaD) completed neuropsychological measures assessing working memory, visuoconstruction, episodic memory, and language. A clinical MRI scan was used to quantify leukoaraiosis, total white matter, hippocampus, lacune, and intracranial volume. We performed analyses to detect the lowest level of leukoaraiosis associated with impairment on the neuropsychological measures. Leukoaraiosis ranged from 0.63% to 23.74% of participants' white matter. Leukoaraiosis explained a significant amount of variance in working memory performance when it involved 3% or more of the white matter with curve estimations showing the relationship to be nonlinear in nature. Greater leukoaraiosis (13%) was implicated for impairment in visuoconstruction. Relationships between leukoaraiosis, episodic memory, and language measures were linear or flat. Leukoaraiosis involves specific threshold points for working memory and visuoconstructional tests in AD/VaD spectrum dementia. These data underscore the need to better understand the threshold at which leukoaraiosis affects and alters the phenotypic expression in insidious onset dementia syndromes.
    Neurology 07/2012; 79(8):734-40. · 8.25 Impact Factor
  • Babette A Brumback, Amy B Dailey, Hao W Zheng
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    ABSTRACT: In social epidemiology, an individual's neighborhood is considered to be an important determinant of health behaviors, mediators, and outcomes. Consequently, when investigating health disparities, researchers may wish to adjust for confounding by unmeasured neighborhood factors, such as local availability of health facilities or cultural predispositions. With a simple random sample and a binary outcome, a conditional logistic regression analysis that treats individuals within a neighborhood as a matched set is a natural method to use. The authors present a generalization of this method for ordinal outcomes and complex sampling designs. The method is based on a proportional odds model and is very simple to program using standard software such as SAS PROC SURVEYLOGISTIC (SAS Institute Inc., Cary, North Carolina). The authors applied the method to analyze racial/ethnic differences in dental preventative care, using 2008 Florida Behavioral Risk Factor Surveillance System survey data. The ordinal outcome represented time since last dental cleaning, and the authors adjusted for individual-level confounding by gender, age, education, and health insurance coverage. The authors compared results with and without additional adjustment for confounding by neighborhood, operationalized as zip code. The authors found that adjustment for confounding by neighborhood greatly affected the results in this example.
    American journal of epidemiology 04/2012; 175(11):1133-41. · 5.59 Impact Factor
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    ABSTRACT: We investigated the psychometric properties of the 68-item Safe Driving Behavior Measure (SDBM) with 80 older drivers, 80 caregivers, and 2 evaluators from two sites. Using Rasch analysis, we examined unidimensionality and local dependence; rating scale; item- and person-level psychometrics; and item hierarchy of older drivers, caregivers, and driving evaluators who had completed the SDBM. The evidence suggested the SDBM is unidimensional, but pairs of items showed local dependency. Across the three rater groups, the data showed good person (≥3.4) and item (≥3.6) separation as well as good person (≥.93) and item reliability (≥.92). Cronbach's α was ≥.96, and few items were misfitting. Some of the items did not follow the hypothesized order of item difficulty. The SDBM classified the older drivers into six ability levels, but to fully calibrate the instrument it must be refined in terms of its items (e.g., item exclusion) and then tested among participants of lesser ability.
    The American journal of occupational therapy.: official publication of the American Occupational Therapy Association 01/2012; 66(2):233-41. · 1.70 Impact Factor
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    ABSTRACT: We used Safe Driving Behavior Measure (SDBM) to determine rater reliability and rater effects (erratic responses, severity, leniency) in three rater groups: 80 older drivers (mean age = 73.26, standard deviation = 5.30), 80 family members or caregivers (age range = 20-85 yr), and two driving evaluators. Rater agreement was significant only between the evaluators and the family members or caregivers. Participants rated driving ability without erratic effects. We observed an overall rater effect only between the evaluator and family members or caregivers, with the evaluators being the more severe rater group. Training family members or caregivers to rate driving behaviors more consistently with the evaluator's ratings may enhance the SDBM's usability and provide a role for occupational therapists to interpret proxy reports as an entry point for logical and efficient driving safety interventions.
    The American journal of occupational therapy.: official publication of the American Occupational Therapy Association 01/2012; 66(1):69-77. · 1.70 Impact Factor
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    ABSTRACT: Objectives  There has been increased attention to access to water, sanitation and hygiene (WASH) at schools in developing countries, but a dearth of empirical studies on the impact. We conducted a cluster-randomized trial of school-based WASH on pupil absence in Nyanza Province, Kenya, from 2007 to 2008. Methods  Public primary schools nested in three geographical strata were randomly assigned and allocated to one of three study arms [water treatment and hygiene promotion (WT & HP), additional sanitation improvement, or control] to assess the effects on pupil absence at 2-year follow-up. Results  We found no overall effect of the intervention on absence. However, among schools in two of the geographical areas not affected by post-election violence, those that received WT and HP showed a 58% reduction in the odds of absence for girls (OR 0.42, CI 0.21-0.85). In the same strata, sanitation improvement in combination with WT and HP resulted in a comparable drop in absence, although results were marginally significant (OR 0.47, 0.21-1.05). Boys were not impacted by the intervention. Conclusion  School WASH improvements can improve school attendance for girls, and mechanisms for gendered impacts should be explored. Incomplete intervention compliance highlights the challenges of achieving consistent results across all settings.
    Tropical Medicine & International Health 12/2011; 17(3):380-391. · 2.94 Impact Factor
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    ABSTRACT: Despite a considerable number of studies describing the relationship between area-level socioeconomic conditions and mammography screening, definitive conclusions have yet to be drawn. The aim of this study was to examine the relationship between area-level socioeconomic position (SEP) and repeat mammography screening, using nationwide U.S. census SEP data linked to a nationally representative sample of women who participated in the 2005 National Health Interview Survey (NHIS). An area-level SEP index using 2000 U.S. census tract data was constructed and categorized into quartiles, including information on unemployment, poverty, housing values, annual family income, education, and occupation. Repeat mammography utilization (dichotomous variable) was defined as having three mammograms over the course of 6 years (24-month interval), which must have included a recent mammogram (in past 2 years). Results were obtained by ordinary multivariable logistic regression for survey data. Women ages 46 to 79 years (n = 7,352) were included in the analysis. In a model adjusted for sociodemographics, health care factors, and known correlates of mammography screening, women living in more disadvantaged areas had lower odds of engaging in repeat mammography than women living in the most advantaged areas [OR comparing quartile 4 (most disadvantaged) to quartile 1 (most advantaged) = 0.63; 95% confidence interval, 0.50-0.80]. The results of this nationwide study support the hypothesis that area-level SEP is independently associated with mammography utilization. These findings underscore the importance of addressing area-level social inequalities, if uptake of mammography screening guidelines is to be realized across all social strata.
    Cancer Epidemiology Biomarkers &amp Prevention 09/2011; 20(11):2331-44. · 4.56 Impact Factor
  • Babette A. Brumback, Zhulin He
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    ABSTRACT: We show via simulation and counterexamples that the Mantel-Haenszel estimator of a common odds ratio, adapted for complex survey designs using survey weights, is inconsistent for sparse-data limiting models. We also propose an alternative estimator that is consistent for sparse-data limiting models satisfying a positivity condition, but not for large-strata limiting models.
    Statistics [?] Probability Letters 09/2011; 81(9):1465-1470. · 0.53 Impact Factor
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    ABSTRACT: The purpose of this study was to quantify and describe the population of young adults with disability in Florida and to assess correlates of healthcare access in this population in contrast with adults belonging to middle and older age groups. This study analyzed data of 36,704 respondents obtained from the 2007 Florida Behavioral Risk Factor Surveillance System. A test for homogeneity of the risk difference across the three age groups was conducted using inverse weighting to adjust for confounding and selection bias. The adjusted model for risk difference of not being able to see a doctor in the past 12 months because of cost was significantly heterogeneous across age groups (χ(2)(2df)F value = 12.40, p < .01). The risk difference between population of young adults with disability and their age peers decreased significantly across the groups. The risk difference was 15.5% for those aged 18-29, 11.9% for those aged 30-64, and 2.1% for those aged ≥65. This article quantifies the differences in risk and access to health care between young adults with and without disability, using population-based data. It provides indirect evidence of the widely held belief that there is a problem in healthcare transition in the United States warranting continued investigation and intervention.
    Journal of Adolescent Health 08/2011; 49(2):219-21. · 2.97 Impact Factor
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    ABSTRACT: Older adults, family members, and professionals may benefit from a safe driving behaviour self-/proxy-report. During development of the Safe Driving Behavior Measure (SDBM), we conducted focus groups to (1) generate items based on respondents' driving experiences, and (2) obtain SDBM item-refinement feedback. Twenty-three older drivers (mean age 70.5, SD = 4.5) and eight family members (mean age 50, SD = 20) from Ontario and Florida described safe driving behaviour (Focus Groups 1 and 2) and critiqued the SDBM (Focus Group 3). We coded responses using content and thematic analyses. Findings from Focus Groups 1 and 2 generated 23 themes (e.g., others' erratic driving) leading to 16 new items (e.g., avoiding collisions). Focus Group 3 findings generated 13 item revisions (e.g., indicating number of highway lanes). Implications. Using focus group findings, we created a version of the SDBM for future testing of construct validity with older drivers.
    Canadian Journal of Occupational Therapy 04/2011; 78(2):72-9. · 0.69 Impact Factor
  • Babette A Brumback, Zhulin He
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    ABSTRACT: Recently, we examined methods of adjusting for confounding by neighborhood of an individual exposure effect on a binary outcome, using complex survey data; the methods were found to fail when the neighborhood sample sizes are small and the selection bias is strongly informative. More recently, other authors have adapted an older method from the genetics literature for application to complex survey data; their adaptation achieves a consistent estimator under a broad range of circumstances. The method is based on weighted pseudolikelihoods, in which the contribution from each neighborhood involves all pairs of cases and controls in the neighborhood. The pairs are treated as if they were independent, a pairwise pseudo-conditional likelihood is thus derived, and then the corresponding score equation is weighted with inverse-probabilities of sampling each case-control pair. We have greatly simplified the implementation by translating the pairwise pseudo-conditional likelihood into an equivalent ordinary weighted log-likelihood formulation. We show how to program the method using standard software for ordinary logistic regression with complex survey data (e.g. SAS PROC SURVEYLOGISTIC). We also show that the methodology applies to a broader set of sampling scenarios than the ones considered by the previous authors. We demonstrate the validity of our simplified implementation by applying it to a simulation for which previous methods failed; the new method performs beautifully. We also apply the new method to an analysis of 2009 National Health Interview Survey (NHIS) public-use data, to estimate the effect of education on health insurance coverage, adjusting for confounding by neighborhood.
    Statistics in Medicine 02/2011; 30(9):965-72. · 2.04 Impact Factor
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    ABSTRACT: The Extension Family Lifestyle Intervention Project (E-FLIP for Kids) is a three-arm, randomized controlled trial assessing the effectiveness of two behavioral weight management interventions in an important and at-risk population, overweight and obese children and their parents in rural counties. Participants will include 240 parent-child dyads from nine rural counties in north central Florida. Dyads will be randomized to one of three conditions: (a) a Family-Based Behavioral Group Intervention, (b) a Parent-Only Behavioral Group Intervention, and (c) an Education Control Condition. Child and parent participants will be assessed at baseline (month 0), post-treatment (month 12) and follow-up (month 24). Assessment and intervention sessions will be held at Cooperative Extension Service offices within each participating county. The primary outcome measure is change in child BMI z-score. Additional key outcome measures include child body fat, waist circumference, dietary intake, physical activity, blood lipids, blood glucose, blood pressure, physical fitness, quality of life, and program and participants costs. Parent BMI, dietary intake, and physical activity also will be assessed. Randomized controlled trials testing the effectiveness of childhood obesity interventions in real-world community-based settings are extremely valuable, but much too rare. The E-FLIP for Kids trial will evaluate the impact of a community-based intervention delivered to families in rural settings utilizing the existing Cooperative Extension Service network on long-term child behavior, weight status and biological markers of diabetes and early cardiovascular disease. If successful, a Parent-Only intervention program may provide a cost-effective and practical intervention for families in underserved rural communities.
    Contemporary clinical trials 01/2011; 32(1):50-8. · 1.51 Impact Factor