Accuracy and reliability of self-reported weight and height in the Sister Study

Objective: To assess the accuracy and reliability of self-reported weight and height and identify the factors associated with reporting accuracy. Design: Analysis of self-reported and measured weight and height from participants in the Sister Study (2003-2009), a nationwide cohort of 50 884 women aged 35-74 years in the USA with a sister with breast cancer. Setting: Weight and height were reported via computer-assisted telephone interview (CATI) and self-administered questionnaires, and measured by examiners. Subjects: Early enrolees in the Sister Study. There were 18 639 women available for the accuracy analyses and 13 316 for the reliability analyses. Results: Using weighted kappa statistics, comparisons were made between CATI responses and examiner measures to assess accuracy and CATI and questionnaire responses to assess reliability. Polytomous logistic regression evaluated factors associated with over- or under-reporting. Compared with measured values, agreement: was 96% for reported height (+/- 1 inch (+/- 2.5 cm); weighted kappa = 0.84) and 67% for weight (+/- 3 lb (+/- 1.36 kg); weighted kappa = 0.92). Obese women (BMI >= 30 kg/m(2)) were more likely than normal-weight women to under-report weight by >= 5% and underweight women (BMI < 18.5 kg/m(2)) were more likely to over-report. Among normal-weight and overweight women (18.5 kg/m(2) <= BMI < 30 kg/m(2)), weight cycling and lifetime weight difference >= 50 lb (>= 22.68 kg) were associated with over-reporting. Conclusions: US women in the Sister Study were reasonably reliable and accurate in reporting weight and height. Women with normal-range BMI reported most accurately. Overweight and obese women and those with weight fluctuations were less accurate, but even among obese women, few under-reported their weight by >10%.