title: Measurement characteristics of the Women's Health Initiative food frequency questionnaire.
abstract: OBJECTIVE
  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 estimate, 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.
authors: Cancer Prevention Research Program, Fred Hutchinson Cancer Research Center, Seattle, WA 98109-1024, USA.
authors: R E
authors: RE
authors: Patterson
authors: A R
authors: AR
authors: Kristal
authors: L F
authors: LF
authors: Tinker
authors: R A
authors: RA
authors: Carter
authors: M P
authors: MP
authors: Bolton
authors: T
authors: T
authors: Agurs-Collins
mesh_terms: D000368:Aged; D004435:Eating; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D011939:Mental Recall; D008875:Middle Aged; D012372:ROC Curve; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D016387:Women's Health