Reproducibility and comparative validity of a food frequency questionnaire for Australian adults.

BACKGROUND Food frequency questionnaires (FFQ) are used in epidemiological studies to investigate the relationship between diet and disease. There is a need for a valid and reliable adult FFQ with a contemporary food list in Australia. AIMS To evaluate the reproducibility and comparative validity of the Australian Eating Survey (AES) FFQ in adults compared to weighed food records (WFRs). METHODS Two rounds of AES and three-day WFRs were conducted in 97 adults (31 males, median age and BMI for males of 44.9 years, 26.2 kg/m(2), females 41.3 years, 24.0 kg/m(2). Reproducibility was assessed over six months using Wilcoxon signed-rank tests and comparative validity was assessed by intraclass correlation coefficients (ICC) estimated by fitting a mixed effects model for each nutrient to account for age, sex and BMI to allow estimation of between and within person variance. RESULTS Reproducibility was found to be good for both WFR and FFQ since there were no significant differences between round 1 and 2 administrations. For comparative validity, FFQ ICCs were at least as large as those for WFR. The ICC of the WFR-FFQ difference for total energy intake was 0.6 (95% CI 0.43, 0.77) and the median ICC for all nutrients was 0.47, with all ICCs between 0.15 (%E from saturated fat) and 0.7 (g/day sugars). CONCLUSIONS Compared to WFR the AES FFQ is suitable for reliably estimating the dietary intakes of Australian adults across a wide range of nutrients.