Errors in Diet Assessment: Impact on Diet-Cancer trials

项目简介：预计2005年美国将有超过50万人死于癌症。关于饮食对癌症影响的调查结果喜忧参半。饮食评估方法的错误导致对饮食对癌症结果影响的估计有偏倚，这可能是饮食-癌症研究缺乏共识的一个解释。本提案的目的是利用一项纵向饮食干预研究的现有数据，量化饮食评估方法的偏倚、可靠性和有效性。本建议中估计的效度系数将提供统计调整因子，可用于获得饮食与癌症关联的校正估计。还将研究饮食评估方法的偏倚对癌症试验设计的影响。分析将集中在正在进行的妇女健康饮食和生活（WHEL）研究上，这是一项随机试验，研究高水果、蔬菜、纤维和低脂肪饮食对乳腺癌复发的影响。这项研究在1995年至2000年间随机抽取了3088名女性，并将于2007年结束。在研究开始、1年和4年时，通过3种方法评估WHEL受试者的饮食暴露：重复24小时回忆访谈；亚利桑那州食物频率调查表；血液样本分析血浆类胡萝卜素浓度（一个标记，与水果/蔬菜摄入量密切相关）。本提案的具体目标是(1)评估血浆标志物随时间的可靠性（2a）开发用于估计自我报告饮食工具偏差和测量误差的模型（2b）评估参与饮食干预是否会减少偏差（2c）检查哪些因素（例如年龄，体型）导致偏差/误差(3)开发（并使公众可用）软件实现本提案中衍生的统计方法。目的1将评估血浆标志物的可靠性测量（类内相关性，受试者内变异系数）。对于目标2，混合效应模型将与“真实”（不可观察的）膳食摄入量（例如正态的混合）的灵活分布相拟合。模拟将用于调查我们的发现的稳健性。相关性：生活方式因素，如饮食和体育活动是可改变的行为，可以预防癌症的发生，提高癌症诊断后的生存率。量化饮食评估工具偏差并纠正这些偏差的统计方法可能导致对饮食与癌症关联的更有效估计。

DESCRIPTION (provided by applicant): Project Summary: Over 500,000 cancer deaths are expected to occur in the US in 2005. Investigations of the impact of diet on cancer have been mixed. Errors in dietary assessment methods lead to biased estimates of the effect of diet on cancer outcomes, a possible explanation for the lack of consensus of diet-cancer studies. The goal of this proposal is to quantify bias, reliability and validity of dietary assessment methods using existing data from a longitudinal dietary intervention study. The validity coefficients estimated in this proposal will provide statistical adjustment factors that can be used to obtain corrected estimates of diet-cancer associations. The implications of bias in dietary assessment methods for the design of cancer trials will also be examined. The analysis will focus on the ongoing Women's Healthy Eating and Living (WHEL) study, a randomized trial examining the effect of a high fruit, vegetable, fiber and low-fat diet on breast cancer recurrence. The study randomized 3088 women between 1995 and 2000, and will close in 2007. The dietary exposure of WHEL subjects is assessed at study entry, 1 and 4 yrs by 3 methods: repeat 24-hour recall interviews; the Arizona Food Frequency Questionnaire; blood samples analyzed for plasma carotenoid concentrations (a marker, well correlated with fruit/vegetable intake). The specific aims of this proposal are (1) To assess the reliability of the plasma marker over time (2a) To develop models for estimating bias and measurement error in self-report dietary instruments (2b) To assess whether participating in a diet intervention reduces bias (2c) To examine what factors (eg age, body-size) contribute to bias/error (3) To develop (and make publicly available) software implementing statistical methods derived in this proposal. Aim 1 will estimate reliability measures (intraclass correlation, within-subject coefficient of variation) for the plasma marker. For Aim 2, mixed-effects models will be fit with flexible distributions for "true" (unobservable) dietary intake (eg mixture of normals). Simulations will be used to investigate the robustness of our findings. Relevance: Lifestyle factors such as diet and physical activity are modifiable behaviors that could protect against cancer incidence and improve survivorship after a cancer diagnosis. Statistical methods that quantify biases in dietary assessment tools and correct these biases could lead to more valid estimates of diet-cancer associations.