Measurement characteristics of the Women's Health Initiative food frequency questionnaire

PURPOSE: The Women's Health Initiative (WHI) is the largest research progra m ever initiated in the United Starts with a focus on diet and health. Ther efore, it is important to understand and document the measurement character istics of the key dietary assessment instrument: the WHI food frequency que stionnaire (FFQ). METHODS: Data are from 113 women screened for participation in the WHI in 1 995. We assessed bias and precision of the FFQ by comparing the intake of 3 0 nutrients estimated from the FFQ with means from four 24-hour dietary rec alls and a 4 day food record. RESULTS: For most nutrients, means estimated by the FFQ were within 10% of the records or recalls. Precision, defined as the correlation between the F FQ and the records and recalls, was similar to other FFQs. Energy adjusted correlation coefficients ranged from 0.2 (vitamin B-12) to 0.7 (magnesium) with a mean of 0.5. The correlation for percentage energy from fat (a key m easure in WHI) was 0.6. Vitamin supplement use was common. For example, alm ost half of total vitamin E intake was obtained from supplements. Including supplemental vitamins and minerals increased micronutrient correlation coe fficients, which ranged from 0.2 (thiamin) to 0.8 (vitamin E) with a mean o f 0.6. CONCLUSIONS: The WHI FFQ produced nutrient estimates that were similar to t hose obtained from short-term dietary recall and recording methods. Compari son of WHI FFQ nutrient intake measures to independent and unbiased measure s, such as doubly labeled water estimates of energy expenditure, are needed to help address the validity of the FFQ in this population. Ann Epidemiol 1999;9:178-187. (C) 1999 Elsevier Science Inc. All rights reserved.