Relative validity and reliability of a quantitative food frequency questionnaire for adults in Guam

BACKGROUND Guam is a US territory in the western Pacific with a diverse population that includes understudied ethnic groups such as Chamorros and Filipinos. A food frequency questionnaire (FFQ) to estimate dietary intake was needed to facilitate studies of diet and health among adults living in Guam. OBJECTIVE To develop and validate an FFQ to assess dietary intake over a 1-year period among adult Guam residents. DESIGN A three-part study was conducted: 1) an initial cross-sectional study using 24-h recalls to identify a food and beverage list for the FFQ and resulting in a final FFQ containing 142 food and drink items; 2) to test reliability, 56 different individuals completed the FFQ twice; and 3) to test relative validity, self-administered FFQs and up to 2 days of food record data from an additional 109 individuals were collected, and daily nutrient intake from the two methods was compared. RESULTS The reliability of the FFQ was very good (ρ range=0.65-0.75), and the relative validity of the FFQ was good for women (median Spearman's correlation [ρ] between instruments of 0.45 across 20 nutrients and an interquartile range [IQR] of 0.42-0.58) and generally adequate for men (median ρ=0.31, IQR=0.23-0.55). Validity was also good for Chamorros (median ρ=0.47, IQR=0.38-0.53) and generally adequate for Filipinos (median ρ=0.42, IQR=0.20-0.62). Correlations after energy adjustment were lower (overall median ρ=0.20, IQR=0.14-0.26). CONCLUSIONS The FFQ can be used to rank nutrient intake for adults in Guam and may be helpful in the analysis of relationships between diet and chronic disease in Guam.