Elsevier

Annals of Epidemiology

Volume 9, Issue 3, April 1999, Pages 178-187
Annals of Epidemiology

Original reports
Measurement Characteristics of the Women’s Health Initiative Food Frequency Questionnaire

https://doi.org/10.1016/S1047-2797(98)00055-6Get rights and content

Abstract

PURPOSE: The Women’s Health Initiative (WHI) is the largest research program ever initiated in the United States with a focus on diet and health. Therefore, it is important to understand and document the measurement characteristics of the key dietary assessment instrument: the WHI food frequency questionnaire (FFQ).

METHODS: Data are from 113 women screened for participation in the WHI in 1995. We assessed bias and precision of the FFQ by comparing the intake of 30 nutrients estimated from the FFQ with means from four 24-hour dietary recalls 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 FFQ and the records and recalls, was similar to other FFQs. Energy adjusted correlation coefficients ranged from 0.2 (vitamin B12) to 0.7 (magnesium) with a mean of 0.5. The correlation for percentage energy from fat (a key measure in WHI) was 0.6. Vitamin supplement use was common. For example, almost half of total vitamin E intake was obtained from supplements. Including supplemental vitamins and minerals increased micronutrient correlation coefficients, which ranged from 0.2 (thiamin) to 0.8 (vitamin E) with a mean of 0.6.

CONCLUSIONS: The WHI FFQ produced nutrient estimates that were similar to those obtained from short-term dietary recall and recording methods. Comparison of WHI FFQ nutrient intake measures to independent and unbiased measures, such as doubly labeled water estimates of energy expenditure, are needed to help address the validity of the FFQ in this population.

Introduction

The Women’s Health Initiative (WHI) is the largest research program ever initiated in the United States whose focus is on diet and health. Approximately 64,500 women, age 50–79, will be randomized in a clinical trial with a partial factorial design to evaluate the health effects of a low-fat dietary pattern, hormone replacement therapy, and calcium/vitamin D supplementation (1). In addition, about 100,000 women will participate in an observational study to examine the associations of known and putative risk factors (and protective factors) with disease. WHI participants will be followed for an average of 9 years. This study has the potential to answer many important questions about dietary intake and the risk of breast cancer, colorectal cancer, heart disease, osteoporosis, and other chronic diseases.

The key dietary assessment instrument in the WHI is the food frequency questionnaire (FFQ). All WHI participants complete an FFQ at baseline and at specified follow-up visits. The FFQ also plays a pivotal role in the low-fat Dietary Modification arm of the Clinical Trial. One of the eligibility criteria is that women must have fat intakes equal to or greater than 32% energy from fat, as determined by screening with the WHI FFQ. The purpose of this screening is to exclude individuals consuming low-fat diets and increase the mean fat intake of the trial participants at baseline, thereby ensuring a substantial difference in dietary fat intake between the control and low-fat intervention groups. All Dietary Modification Trial participants complete FFQs at baseline (before randomization) and year 1, and these data are used to evaluate the effectiveness of the dietary intervention. Finally, random subsamples of trial participants complete an FFQ annually, to monitor maintenance of the low-fat diet in the intervention group and secular trends in dietary intake in the control group.

The WHI FFQ was designed by an ad hoc dietary assessment working group composed of WHI scientists and was implemented by the WHI Clinical Coordinating Center. Because one component of the WHI is a low-fat diet intervention, we included many questions on low-fat food preparation methods and reduced-fat foods to make the FFQ sensitive to fat intake (2). In addition, we designed the instrument to reflect regional and ethnic eating patterns in the United States. Many examples of southern foods were added to the questionnaire (e.g., okra was added to the food item: “Summer squash, such as zucchini”), 12 foods were added to reflect Hispanic eating patterns, and Indian fry bread was included for Native Americans. Because the WHI FFQ is a major revision of the instrument used in the Women’s Health Trial Feasibility Study in Minority Populations (3), it is important to evaluate its measurement characteristics (4).

The purpose of this dietary assessment study was to investigate the measurement characteristics of the WHI FFQ as compared to short-term dietary recall and recording methods. In this report, we assess the agreement of intakes of 30 nutrients estimated using the WHI FFQ as compared with corresponding estimates from a 4-day food record and four 24-hour dietary recalls. We also present data pertinent to the sensitivity and specificity of the FFQ as a screening tool for selecting participants with fat intakes equal to or greater than 32% energy from fat.

Section snippets

Participants

WHI is funded and directed by the National Institutes of Health (NIH) and coordinated by the WHI Clinical Coordinating Center at the Fred Hutchinson Cancer Research Center. The NIH named the 16 Vanguard Clinical Centers in 1993 and an additional 24 Clinical Centers in 1994. A list of the WHI investigators and centers has been published (5).

Data reported herein are from 113 women screened for participation in WHI by the 16 Vanguard Clinical Centers in 1995. Each of the Clinical Centers enrolled

Results

The mean age of the dietary assessment study participants was 63, about 80% were Caucasian, 70% had completed more than high school, 40% had household incomes greater than $50,000, 50% were overweight or obese, and 25% used at least one type of vitamin supplement (Table 1). Differences between dietary assessment study participants and the WHI comparison group were modest, except that about 18% of assessment study participants were African American as compared with only 10% of the WHI comparison

Discussion

The WHI FFQ has measurement properties that are similar to or better than those reported for other FFQs in similar populations. Table 5 gives correlation coefficients between the WHI, Willett 18, 19 and Block/NCI FFQs (20) and records or recalls in studies of older women. Correlation coefficients for the WHI FFQ were higher for fiber, folate, calcium, and iron and almost identical for fat, carbohydrate, protein, and cholesterol. Correlation coefficients for the WHI FFQ were somewhat lower for

Acknowledgements

The Women’s Health Initiative Clinical Coordinating Center is supported by contract N01-WH-2-2110 from the National Institutes of Health. The Women’s Health Initiative Investigators Group: Program Office: (National Institutes of Health, Bethesda, Maryland) Carolyn K. Clifford, Suzanne Hurd, Joan A. McGowan, Linda Pottern, Jacques E. Rossouw. Clinical Coordinating Center: (Fred Hutchinson Cancer Research Center, Seattle, WA) Ross Prentice, Maureen Henderson, Garnet Anderson, Andrea LaCroix, Anne

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