Reproducibility and Intermethod Reliability of a Calcium Food Frequency Questionnaire for Use in Hispanic, Non-Hispanic Black, and Non-Hispanic White Youth

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 (lambda=0.20) and Hispanics (lambda=0.26) than for non-Hispanic whites (lambda=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.