Background: A dietary assessment instrument designed for use in a nationally representative pediatric population was required to examine associations between calcium intake and bone mineral accrual in a large, multicenter study.
Objective: To determine the reproducibility and intermethod reliability of a youth calcium food frequency questionnaire (FFQ) in a multiracial/ethnic sample of children and adolescents.
Design: Reproducibility (n=69) and intermethod reliability (n=393) studies were conducted by administering repeat FFQs and three unannounced 24-hour dietary recalls to stratified random samples of individuals participating in the Bone Mineral Density in Childhood Study.
Participants/setting: Children and adolescents ages 5 to 21 years.
Main outcome measures: Calcium intake estimated from the FFQ and 24-hour dietary recalls.
Statistical analysis: Reproducibility was assessed by the intraclass correlation coefficient (ICC). Intermethod reliability was assessed by deattenuated Pearson correlations between the FFQ and 24-hour recalls. Attenuation factors and calibration corrected effect estimates for bone density were calculated to determine the potential influence of measurement error on associations with health outcomes.
Results: The ICC (0.61) for repeat administrations and deattenuated Pearson correlation between the FFQ and 24-hour recalls (r=0.60) for all subjects indicated reproducibility and intermethod reliability (Pearson r=0.50 to 0.74 across sex and age groups). Attenuation factors were ≤0.50 for all sex and age groups and lower for non-Hispanic blacks (λ=0.20) and Hispanics (λ=0.26) than for non-Hispanic whites (λ=0.42).
Conclusions: The Bone Mineral Density in Childhood Study calcium FFQ appears to provide a useful tool for assessing calcium intake in children and adolescents drawn from multiracial/ethnic populations and/or spanning a wide age range. However, similar to other FFQs, attenuation factors were substantially <1, indicating the potential for appreciable measurement error bias. Calibration correction should be performed and racial/ethnic differences in performance considered when analyzing and interpreting findings based on this instrument.
Keywords: Calibration; Diet; Diet recall; Nutrition assessment; Questionnaires.
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