未测量的混杂因素是否会影响零售食品环境与体重指数之间随时间的关联？冠状动脉风险发展在年轻人（CARDIA）研究。
Does unmeasured confounding influence associations between the retail food environment and body mass index over time? The Coronary Artery Risk Development in Young Adults (CARDIA) study.
机构信息
Department of Nutrition, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, NC, USA.
Carolina Population Center, Chapel Hill, North Carolina.
出版信息
Int J Epidemiol. 2017 Oct 1;46(5):1456-1464. doi: 10.1093/ije/dyx070.
BACKGROUND
Findings in the observational retail food environment and obesity literature are inconsistent, potentially due to a lack of adjustment for residual confounding.
METHODS
Using data from the CARDIA study (n = 12 174 person-observations; 6 examinations; 1985-2011) across four US cities (Birmingham, AL; Chicago, IL; Minneapolis, MN; Oakland, CA), we used instrumental-variables (IV) regression to obtain causal estimates of the longitudinal associations between the percentage of neighbourhood food stores or restaurants (per total food outlets within 1 km network distance of respondent residence) with body mass index (BMI), adjusting for individual-level socio-demographics, health behaviours, city, year, total food outlets and market-level prices. To determine the presence and extent of bias, we compared the magnitude and direction of results with ordinary least squares (OLS) and random effects (RE) regression, which do not control for residual confounding, and with fixed effects (FE) regression, which does not control for time-varying residual confounding.
RESULTS
Relative to neighbourhood supermarkets (which tend to be larger and have healthier options than grocery stores), a higher percentage of grocery stores [mean = 53.4%; standard deviation (SD) = 31.8%] was positively associated with BMI [β = 0.05; 95% confidence interval (CI) = 0.01, 0.10] using IV regression. However, associations were negligible or null using OLS (β = -0.001; 95% CI = -0.01, 0.01), RE (β = -0.003; 95% CI = -0.01, 0.0001) and FE (β = -0.003; 95% CI = -0.01, 0.0002) regression. Neighbourhood convenience stores and fast-food restaurants were not associated with BMI in any model.
CONCLUSIONS
Longitudinal associations between neighbourhood food outlets and BMI were greater in magnitude using a causal model, suggesting that weak findings in the literature may be due to residual confounding.
背景
观察性零售食品环境与肥胖文献中的研究结果并不一致，这可能是由于缺乏对残余混杂因素的调整。
方法
利用美国四个城市（阿拉巴马州伯明翰市、伊利诺伊州芝加哥市、明尼苏达州明尼阿波利斯市、加利福尼亚州奥克兰市）的 CARDIA 研究（n=12174 人次观察；6 次检查；1985-2011 年）的数据，我们使用工具变量（IV）回归来获得邻里食品店或餐馆比例（受访者居住地 1 公里网络距离内的总食品店数量）与体重指数（BMI）之间纵向关联的因果估计值，调整个体水平的社会人口统计学、健康行为、城市、年份、总食品店和市场水平价格。为了确定是否存在偏见及其程度，我们将结果与普通最小二乘法（OLS）和随机效应（RE）回归进行了比较，后者不控制残余混杂因素，与固定效应（FE）回归进行了比较，后者不控制时变残余混杂因素。
结果
与邻里超市（通常比杂货店更大，提供更健康的选择）相比，杂货店比例较高（均值=53.4%；标准差[SD]=31.8%）与 BMI 呈正相关（β=0.05；95%置信区间[CI]：0.01，0.10），采用 IV 回归。然而，使用 OLS（β=-0.001；95%CI：-0.01，0.01）、RE（β=-0.003；95%CI：-0.01，0.0001）和 FE（β=-0.003；95%CI：-0.01，0.0002）回归，关联则微不足道或为零。邻里便利店和快餐店与 BMI 均无关联。
结论
使用因果模型时，邻里食品店与 BMI 之间的纵向关联在幅度上更大，这表明文献中的微弱发现可能归因于残余混杂因素。
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