Chanelle J Howe

Brown University, Providence, Rhode Island, United States

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Publications (19)76.72 Total impact

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    ABSTRACT: Selection bias due to loss to follow up represents a threat to the internal validity of estimates derived from cohort studies. Over the last fifteen years, stratification-based techniques as well as methods such as inverse probability-of-censoring weighted estimation have been more prominently discussed and offered as a means to correct for selection bias. However, unlike correcting for confounding bias using inverse weighting, uptake of inverse probability-of-censoring weighted estimation as well as competing methods has been limited in the applied epidemiologic literature. To motivate greater use of inverse probability-of-censoring weighted estimation and competing methods, we use causal diagrams to describe the sources of selection bias in cohort studies employing a time-to-event framework when the quantity of interest is an absolute measure (e.g. absolute risk, survival function) or relative effect measure (e.g., risk difference, risk ratio). We highlight that whether a given estimate obtained from standard methods is potentially subject to selection bias depends on the causal diagram and the measure. We first broadly describe inverse probability-of-censoring weighted estimation and then give a simple example to demonstrate in detail how inverse probability-of-censoring weighted estimation mitigates selection bias and describe challenges to estimation. We then modify complex, real-world data from the University of North Carolina Center for AIDS Research HIV clinical cohort study and estimate the absolute and relative change in the occurrence of death with and without inverse probability-of-censoring weighted correction using the modified University of North Carolina data. We provide SAS code to aid with implementation of inverse probability-of-censoring weighted techniques.
    No preview · Article · Oct 2015 · Epidemiology (Cambridge, Mass.)
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    ABSTRACT: Purpose: To evaluate whether dispositional mindfulness (defined as the ability to attend nonjudgmentally to one's own physical and mental processes) is associated with obesity and central adiposity. Methods: Study participants (n = 394) were from the New England Family Study, a prospective birth cohort, with median age 47 years. Dispositional mindfulness was assessed using the Mindful Attention Awareness Scale (MAAS). Central adiposity was assessed using dual-energy X-ray absorptiometry (DXA) scans with primary outcomes android fat mass and android/gynoid ratio. Obesity was defined as body mass index ≥30 kg/m(2). Results: Multivariable-adjusted regression analyses demonstrated that participants with low vs. high MAAS scores were more likely to be obese (prevalence ratio for obesity = 1.34 (95 % confidence limit (CL): 1.02, 1.77)), adjusted for age, gender, race/ethnicity, birth weight, childhood socioeconomic status, and childhood intelligence. Furthermore, participants with low vs. high MAAS level had a 448 (95 % CL 39, 857) g higher android fat mass and a 0.056 (95 % CL 0.003, 0.110) greater android/gynoid fat mass ratio. Prospective analyses demonstrated that participants who were not obese in childhood and became obese in adulthood (n = 154) had -0.21 (95 % CL -0.41, -0.01; p = 0.04) lower MAAS scores than participants who were not obese in childhood or adulthood (n = 203). Conclusions: Dispositional mindfulness may be inversely associated with obesity and adiposity. Replication studies are needed to adequately establish whether low dispositional mindfulness is a risk factor for obesity and adiposity.
    No preview · Article · Oct 2015 · International Journal of Behavioral Medicine
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    Chanelle J. Howe · Lauren E. Cain · Joseph W. Hogan
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    ABSTRACT: Estimating causal effects is a frequent goal of epidemiologic studies. Traditionally, there have been three established systematic threats to consistent estimation of causal effects. These three threats are bias due to confounders, selection, and measurement error. Confounding, selection, and measurement bias have typically been characterized as distinct types of biases. However, each of these biases can also be characterized as missing data problems that can be addressed with missing data solutions. Here we describe how the aforementioned systematic threats arise from missing data as well as review methods and their related assumptions for reducing each bias type. We also link the assumptions made by the reviewed methods to the missing completely at random (MCAR) and missing at random (MAR) assumptions made in the missing data framework that allow for valid inferences to be made based on the observed, incomplete data.
    Preview · Article · Jul 2015
  • Hirut T Gebrekristos · Chanelle J Howe

    No preview · Article · Jan 2015 · Epidemiology (Cambridge, Mass.)
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    ABSTRACT: Objective. Education is inversely associated with coronary heart disease (CHD) risk; however the mechanisms are poorly understood. The study objectives were to evaluate the extent to which rarely measured factors (literacy, time preference, sense of control) and more commonly measured factors (income, depressive symptomatology, body mass index) in the education-CHD literature explain the associations between education and CHD risk. Method. The study sample included 346 participants, aged 38 to 47 years (59.5% women), of the New England Family Study birth cohort. Ten-year CHD risk was calculated using the validated Framingham risk algorithm that utilizes diabetes, smoking, blood pressure, total cholesterol, high-density lipoprotein cholesterol, age, and gender. Multivariable regression and mediation analyses were performed. Results. Regression analyses adjusting for age, race/ethnicity, and childhood confounders (e.g., parental socioeconomic status, intelligence) demonstrated that relative to those with greater than or equal to college education, men and women with less than high school had 73.7% (95% confidence interval [CI; 29.5, 133.0]) and 48.2% (95% CI [17.5, 86.8]) higher 10-year CHD risk, respectively. Mediation analyses demonstrated significant indirect effects for reading comprehension in women (7.2%; 95% CI [0.7, 19.4]) and men (7.2%; 95% CI [0.8, 19.1]), and depressive symptoms (11.8%; 95% CI [2.5, 26.6]) and perceived constraint (6.7%, 95% CI [0.7, 19.1]) in women. Conclusions. Evidence suggested that reading comprehension in women and men, and depressive symptoms and perceived constraint in women, may mediate some of the association between education and CHD risk. If these mediated effects are interpreted causally, interventions targeting reading, depressive symptoms, and perceived constraint could reduce educational inequalities in CHD. © 2014 Society for Public Health Education.
    No preview · Article · Nov 2014 · Health Education & Behavior
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    ABSTRACT: Background In Denmark, the first standalone supervised injecting facility (SIF) opened in Copenhagen’s Vesterbro neighborhood on October 1, 2012. The purpose of this study was to assess whether use of services provided by the recently opened SIF was associated with changes in injecting behavior and syringe disposal practices among people who inject drugs (PWID). We hypothesized that risk behaviors (e.g., syringe sharing), and unsafe syringe disposal (e.g., dropping used equipment on the ground) had decreased among PWID utilizing the SIF. Methods Between February and August of 2013, we conducted interviews using a survey (in English and Danish) with forty-one people who reported injecting drugs at the SIF. We used descriptive statistics and McNemar’s test to examine sociodemographic characteristics of the sample, current drugs used, sites of syringe disposal before and after opening of the SIF, and perceived behavior change since using the SIF. Results Of the interviewed participants, 90.2% were male and the majority were younger than 40 years old (60.9%). Three-quarters (75.6%) of participants reported reductions in injection risk behaviors since the opening of the SIF, such as injecting in a less rushed manner (63.4%), fewer outdoor injections (56.1%), no longer syringe sharing (53.7%), and cleaning injecting site(s) more often (43.9%). Approximately two-thirds (65.9%) of participants did not feel that their frequency of injecting had changed; five participants (12.2%) reported a decrease in injecting frequency, and only two participants (4.9%) reported an increase in injecting frequency. Twenty-four (58.5%) individuals reported changing their syringe disposal practices since the opening of the SIF; of those, twenty-three (95.8%) reported changing from not always disposing safely to always disposing safely (McNemar’s test p-value < 0.001). Conclusions Our findings suggest that use of the Copenhagen SIF is associated with adoption of safer behaviors that reduce harm and promote health among PWID, as well as practices that benefit the Vesterbro neighborhood (i.e., safer syringe disposal). As a public health intervention, Copenhagen’s SIF has successfully reached PWID engaging in risk behavior. To fully characterize the impacts of this and other Danish SIFs, further research should replicate this study with a larger sample size and prospective follow-up.
    Full-text · Article · Oct 2014 · Harm Reduction Journal
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    ABSTRACT: Background Mindfulness (the ability to attend nonjudgmentally to one’s own physical and mental processes) is receiving substantial interest as a potential determinant of health. However, little is known whether mindfulness is associated with cardiovascular health. Purpose The aim of this study is to evaluate whether dispositional mindfulness is associated with cardiovascular health. Method Study participants (n = 382) were from the New England Family Study, born in Providence, RI, USA, with mean age 47 years. Dispositional mindfulness was assessed using the Mindful Attention Awareness Scale (MAAS). Cardiovascular health was assessed based on American Heart Association criteria. Cross-sectional multivariable-adjusted log binomial regression analyses were performed. Results Analyses demonstrated that those with high vs. low MAAS had prevalence ratio (PR) for good cardiovascular health of 1.83 (95 % confidence interval (CI) 1.07, 3.13), adjusted for age, gender, and race/ethnicity. There were significant associations of high vs. low mindfulness with nonsmoking (PR = 1.37, 95 % CI 1.06, 1.76), body mass index
    No preview · Article · Oct 2014 · International Journal of Behavioral Medicine
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    ABSTRACT: Objective To determine whether HIV status and knowledge of mother-to-child-transmission (MTCT) of HIV are associated with antenatal care (ANC) use. Methods Data were obtained from the 2011 Ethiopia Demographic and Health Survey among women aged 15–49 years who agreed to HIV testing and who reported giving birth in the preceding five years. The two exposures of interest were HIV status and knowledge of MTCT. Unadjusted and adjusted prevalence ratios for ANC use were estimated by fitting modified Poisson regression models. Results Among the 7392 women in the sample, ANC use was lowest among HIV-negative, low MTCT knowledge women (31.6% [95% confidence interval: 28.1–35.1]), and highest among HIV-positive, high knowledge women (81.9% [69.8–94.0%]). ANC use was significantly higher among HIV-positive, high knowledge (adjusted prevalence ratio [APR] = 1.60 [1.32–1.94]) and HIV-negative, high knowledge women (1.37 [1.24–1.51]) compared with HIV-negative, low knowledge women. There was no statistically significant difference in ANC use by HIV status among low knowledge women (1.26 [0.71–2.25]). Conclusions HIV-positive women generally had better MTCT knowledge. Among HIV-negative women, the prevalence of ANC use was greater among women with higher knowledge. Increasing MTCT knowledge may facilitate ANC use and in turn may eliminate MTCT.
    Full-text · Article · Sep 2014 · Journal of Epidemiology and Global Health
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    ABSTRACT: Background: Early-life exposure to bisphenol A (BPA) may increase childhood obesity risk, but few prospective epidemiological studies have investigated this relationship. Objective: We sought to determine whether early-life exposure to BPA was associated with increased body mass index (BMI) at 2-5 years of age in 297 mother-child pairs from Cincinnati, Ohio (HOME Study). Methods: Urinary BPA concentrations were measured in samples collected from pregnant women during the second and third trimesters and their children at 1 and 2 years of age. BMI z-scores were calculated from weight/height measures conducted annually from 2 through 5 years of age. We used linear mixed models to estimate BMI differences or trajectories with increasing creatinine-normalized BPA concentrations. Results: After confounder adjustment, each 10-fold increase in prenatal (β = -0.1; 95% CI: -0.5, 0.3) or early-childhood (β = -0.2; 95% CI: -0.6, 0.1) BPA concentrations was associated with a modest and nonsignificant reduction in child BMI. These inverse associations were suggestively stronger in girls than in boys [prenatal effect measure modification (EMM) p-value = 0.30, early-childhood EMM p-value = 0.05], but sex-specific associations were imprecise. Children in the highest early-childhood BPA tercile had lower BMI at 2 years (difference = -0.3; 95% CI: -0.6, 0.0) and larger increases in their BMI slope from 2 through 5 years (BMI increase per year = 0.12; 95% CI: 0.07, 0.18) than children in the lowest tercile (BMI increase per year = 0.07; 95% CI: 0.01, 0.13). All associations were attenuated without creatinine normalization. Conclusions: Prenatal and early-childhood BPA exposures were not associated with increased BMI at 2-5 years of age, but higher early-childhood BPA exposures were associated with accelerated growth during this period.
    Full-text · Article · Jul 2014 · Environmental Health Perspectives
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    ABSTRACT: Racial disparities in clinic attendance may contribute to racial disparities in plasma human immunodeficiency virus type 1 (HIV-1) RNA levels among HIV-positive patients in care. Data from 946 African American and 535 Caucasian patients receiving HIV care at the University of North Carolina Center for AIDS Research HIV clinic between January 1, 1999, and August 1, 2012, were used to estimate the association between African American race and HIV virological suppression (i.e., undetectable HIV-1 RNA) when racial disparities in clinic attendance were lessened. Clinic attendance was measured as the proportion of scheduled clinic appointments attended (i.e., visit adherence) or the proportion of six 4-month intervals with at least 1 attended scheduled clinic appointment (i.e., visit constancy). In analyses accounting for patient characteristics, the risk ratio for achieving suppression when comparing African Americans with Caucasians was 0.91 (95% confidence interval: 0.85, 0.98). Lessening disparities in adherence or constancy lowered disparities in virological suppression by up to 44.4% and 11.1%, respectively. Interventions that lessen disparities in adherence may be more effective in eliminating disparities in suppression than interventions that lessen disparities in constancy. Given that gaps in care were limited to be no more than 2 years for both attendance measures, the impact of lessening disparities in adherence may be overstated. © 2014 The Author 2014. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: [email protected] /* */
    Preview · Article · May 2014 · American journal of epidemiology
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    ABSTRACT: Introduction Studies examining the use of pre-exposure prophylaxis (PrEP) to prevent HIV transmission among people who inject drugs (PWIDs) have not been adequately summarized. Recently, the Bangkok Tenofovir Study has shown that PrEP may be effective at reducing new HIV infections among this high-risk group. This randomized controlled trial was the first study to specifically examine the efficacy of PrEP among PWIDs. In this review, we present the current state of evidence regarding the use of PrEP to prevent HIV infection in PWID populations, and set an agenda for future research to inform the most effective implementation of PrEP in the context of existing evidence-based HIV prevention strategies. Discussion Despite positive trial results confirming that PrEP may prevent HIV transmission among PWIDs, there remain many questions regarding the interpretation of these results, as well as obstacles to the implementation of PrEP regimens within highly diverse drug-using communities. Aside from the Bangkok Tenofovir Study, we identified only one other published study that has collected empirical data to inform the use of PrEP among PWIDs. The large gap in research regarding the use and implementation of PrEP for PWIDs signals the need for further research and attention. Conclusions We recommend that future research efforts focus on elucidating the generalizability of the Bangkok Tenofovir Study results in other injection drug–using populations, examining the willingness of PWIDs to use PrEP in diverse contexts, identifying barriers to adherence to PrEP regimens and determining the most effective ways to implement PrEP programmes within the context of existing evidence-based prevention strategies, including opioid substitution therapy and needle and syringe distribution programmes.
    Full-text · Article · Mar 2014 · Journal of the International AIDS Society
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    ABSTRACT: The causes of poor clinic attendance and incomplete virologic suppression among HIV+ African Americans (AAs) are not well understood. We estimated the effect of at-risk alcohol/drug use and associated treatment on attending scheduled appointments and virologic suppression among 576 HIV+ AA patients in the UAB 1917 Clinic Cohort who contributed 591 interviews to the analysis. At interview, 78% of patients were new to HIV care at UAB, 38% engaged in at-risk alcohol/drug use or received associated treatment in the prior year, while the median (quartiles) age and CD4 count were 36 (28; 46) years and 321 (142; 530) cells/microl, respectively. In the two years after an interview, half of patients had attended at least 82% of appointments while half had achieved virologic suppression for at least 71% of RNA assessments. Compared to patients who did not use or receive treatment, the adjusted risk ratio (aRR) for attending appointments for patients who did use but did not receive treatment was 0.97 (95% confidence limits: 0.92, 1.03). The corresponding aRR for virologic suppression was 0.94 (0.86, 1.03). Compared to patients who did not receive treatment but did use, the aRR for attending appointments for patients who did receive treatment and did use was 0.86 (0.78, 0.95). The corresponding aRR for virologic suppression was 1.07 (0.92, 1.24). Use was negatively associated with attendance and virologic suppression among patients not in treatment. Among users, treatment was negatively associated with attendance yet positively associated with virologic suppression. However, aRR estimates were imprecise.
    No preview · Article · Dec 2013 · AIDS research and human retroviruses
  • Chanelle J Howe · Stephen R Cole · Shruti H Mehta · Gregory D Kirk
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    ABSTRACT: The joint effects of multiple exposures on an outcome are frequently of interest in epidemiologic research. In 2001, Hernán et al (J Am Stat Assoc. 2001;96:440-448) presented methods for estimating the joint effects of multiple time-varying exposures subject to time-varying confounding affected by prior exposure using joint marginal structural models. Nonetheless, the use of these joint models is rare in the applied literature. Minimal uptake of these joint models, in contrast to the now widely used standard marginal structural model, is due in part to a lack of examples demonstrating the method. In this paper, we review the assumptions necessary for unbiased estimation of joint effects as well as the distinction between interaction and effect measure modification. We demonstrate the use of marginal structural models for estimating the joint effects of alcohol consumption and injection drug use on HIV acquisition, using data from 1525 injection drug users in the AIDS Link to Intravenous Experience cohort study. In the joint model, the hazard ratio (HR) for heavy drinking in the absence of any drug injections was 1.58 (95% confidence interval = 0.67-3.73). The HR for any drug injections in the absence of heavy drinking was 1.78 (1.10-2.89). The HR for heavy drinking and any drug injections was 2.45 (1.45-4.12). The P values for multiplicative and additive interaction were 0.7620 and 0.9200, respectively, indicating a lack of departure from effects that multiply or add. We could not rule out interaction on either scale due to imprecision.
    No preview · Article · Apr 2012 · Epidemiology (Cambridge, Mass.)
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    Full-text · Article · Nov 2011 · Epidemiology (Cambridge, Mass.)
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    Preview · Article · Aug 2011 · American Journal of Clinical Nutrition
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    Chanelle J Howe · Stephen R Cole · Joan S Chmiel · Alvaro Muñoz
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    ABSTRACT: In time-to-event analyses, artificial censoring with correction for induced selection bias using inverse probability-of-censoring weights can be used to 1) examine the natural history of a disease after effective interventions are widely available, 2) correct bias due to noncompliance with fixed or dynamic treatment regimens, and 3) estimate survival in the presence of competing risks. Artificial censoring entails censoring participants when they meet a predefined study criterion, such as exposure to an intervention, failure to comply, or the occurrence of a competing outcome. Inverse probability-of-censoring weights use measured common predictors of the artificial censoring mechanism and the outcome of interest to determine what the survival experience of the artificially censored participants would be had they never been exposed to the intervention, complied with their treatment regimen, or not developed the competing outcome. Even if all common predictors are appropriately measured and taken into account, in the context of small sample size and strong selection bias, inverse probability-of-censoring weights could fail because of violations in assumptions necessary to correct selection bias. The authors used an example from the Multicenter AIDS Cohort Study, 1984-2008, regarding estimation of long-term acquired immunodeficiency syndrome-free survival to demonstrate the impact of violations in necessary assumptions. Approaches to improve correction methods are discussed.
    Preview · Article · Feb 2011 · American journal of epidemiology
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    ABSTRACT: to estimate the effect of alcohol consumption on HIV acquisition while appropriately accounting for confounding by time-varying risk factors. african-American injection drug users in the AIDS Link to Intravenous Experience cohort study. Participants were recruited and followed with semiannual visits in Baltimore, Maryland between 1988 and 2008. marginal structural models were used to estimate the effect of alcohol consumption on HIV acquisition. at entry, 28% of 1525 participants were women with a median (quartiles) age of 37 (32-42) years and 10 (10-12) years of formal education. During follow-up, 155 participants acquired HIV and alcohol consumption was 24, 24, 26, 17, and 9% for 0, 1-5, 6-20, 21-50, and 51-140 drinks per week over the prior 2 years, respectively. In analyses accounting for sociodemographic factors, drug use, and sexual activity, hazard ratios for participants reporting 1-5, 6-20, 21-50, and 51-140 drinks per week in the prior 2 years compared to participants who reported 0 drinks per week were 1.09 (0.60-1.98), 1.18 (0.66-2.09), 1.66 (0.94-2.93), and 2.12 (1.15-3.90), respectively. A trend test indicated a dose-response relationship between alcohol consumption and HIV acquisition (P value for trend = 9.7 × 10). a dose-response relationship between alcohol consumption and subsequent HIV acquisition is indicated, independent of measured known risk factors.
    Full-text · Article · Jan 2011 · AIDS (London, England)
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    Chanelle J Howe · Stephen R Cole · Sonia Napravnik · Joseph J Eron
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    ABSTRACT: Predictors of study retention and scheduled visit attendance in the University of North Carolina Center for AIDS Research (UNC CFAR) prospective clinical cohort of HIV-infected patients enrolled between 1 January 2001 and 1 January 2008 are reported. At study entry, 1636 participants were 32% female, 58% were African-American, 49% had not received HIV care elsewhere, 71% were receiving or initiated combination antiretroviral therapy, and 26% were diagnosed with AIDS, with median (quartiles) age of 40 (34; 47) years, distance to clinic of 45 (21; 70) miles, HIV-1 RNA of 1396 (200; 26,750) copies/ml, and CD4 of 374 (182; 602) cells/mm(3). Participants contributed a median of 7 (4; 13) scheduled visits and 2.25 (1.0; 3.9) years alive under follow-up. During 6134 person-years of follow-up, 414 participants dropped out and 145 died. Accounting for differences in death by participant characteristics, the 6-year cumulative probability of retention was 67% [95% confidence limits (CL): 65, 70%], with 6.75 (95% CL: 6.13, 7.43) drop outs per 100 person-years. In a multivariable Cox proportional hazards model, retention was higher among participants who were insured, had not received HIV care elsewhere, had controlled HIV viremia, and were living in nonurban areas or proximate to the clinic. In a multivariable modified Poisson regression model that accounted for differences in drop out and death by participant characteristics, visit attendance was higher among older, AIDS-diagnosed, immune compromised, and cART-initiated participants. The UNC CFAR clinical cohort has ample enrollment with retention and visit attendance modestly influenced by factors such as disease severity.
    Preview · Article · Aug 2010 · AIDS research and human retroviruses
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    ABSTRACT: Discuss issues related to time-varying exposures using as an example the recently meta-analyzed literature (Baliunas et al. in Int J Public Health, 2009) on alcohol consumption and risk of HIV infection. Cataloged sources of bias and imprecision in the context of time-varying exposures. Confounding, selection, or measurement bias may occur when standard regression approaches are used to estimate effects of time-varying exposures. The reviewed literature on alcohol consumption and HIV infection suffer from one or more of these biases. Detailed prospective data and thoughtful implementation of appropriate statistical methods are needed to obtain unbiased estimates of time-varying exposures, such as alcohol consumption.
    No preview · Article · Feb 2010 · International Journal of Public Health