Objective: To evaluate the reliability and relative validity of a semi-quantitative FFQ for assessing the habitual intake of multiple nutrients in New Zealand (NZ) adults over the past 12 months.
Design: A 154-item FFQ was developed. After initial pre-testing, reliability was assessed using intra-class correlations. Relative validity was assessed by comparing nutrient intakes derived from the FFQ v. those from an 8 d diet record (8dWDR) collected over 12 months and selected blood biomarkers, using Spearman correlations. Supplementary cross-classification and Bland-Altman analyses were performed to assess validity of the FFQ v. the 8dWDR.
Setting: Dunedin, NZ.
Subjects: One hundred and thirty-two males and females aged 30-59 years who completed all FFQ and 8dWDR and provided a blood sample.
Results: Reliability coefficients ranged from 0·47 for Ca to 0·83 for alcohol, with most values falling between 0·60 and 0·80. The highest validity coefficients for energy-adjusted data were observed for alcohol (0·74), cholesterol (0·65) and β-carotene (0·58), and the lowest for Zn (0·24) and Ca (0·28). For all energy-adjusted nutrients mean percentage correct classification was 77·9% and gross misclassification was 4·5%. Results of Bland-Altman analyses showed wide limits of agreement for all micronutrients but high agreement was observed for most macronutrients (99% for protein, 103% for total fat). When compared with biomarkers, energy-adjusted coefficients were 0·34 for β-carotene and 0·33 for vitamin C.
Conclusions: The FFQ provides highly repeatable measurements and good validity in ranking individuals' intake, suggesting that it will be a useful tool to assess nutrient intake of NZ adults in future research.