Assessing lifetime diet: reproducibility of a self-administered, non-quantitative FFQ

Objective: To demonstrate test-retest reliability (reproducibility) of a new self-administered lifetime diet questionnaire, with a focus on foods relevant to cognitive health in older age. Design: The reproducibility of dietary recall over four or five life periods was assessed by administering the questionnaire at two time points to an older cohort. The period between questionnaire administrations was 7 weeks. Polychoric correlations measured the association between recall at time 1 and time 2 and the weighted kappa statistic measured the level of recall agreement for food groups across the two administrations of the questionnaire. Setting: Adelaide, South Australia. Subjects: Fifty-two cognitively healthy, older-age, community-dwelling adults completed the Lifetime Diet Questionnaire; mean age 81.8 (SD 4.4) years, range 70-90 years. Results: The questionnaire showed very good reproducibility in this sample with a mean polychoric correlation coefficient of 0.81 between administration at time 1 and time 2, and an average weighted kappa of 0.49 for the level of recall agreement between food groups. Conclusions: The demonstrated reliability of this lifetime diet questionnaire makes it a useful tool to assess potential relationships between long-term dietary intake and later-age cognitive outcomes.