Determining the relative validity and reproducibility of a food frequency questionnaire (FFQ) to assess nutrient intake in older adults living in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics at Massey University, Albany, New Zealand
Background: New Zealand’s population is ageing. Dietary intakes in older adults and
physiological changes through ageing are important predictors of health and disease
outcomes. However, it is challenging to capture the typical diet of older adults. Among
different types of dietary assessment tools, a food frequency questionnaire (FFQ) is easy to
administer and causes less burden to participants. To the best of our knowledge, the latest
FFQ validation study in older adults was undertaken nearly 30 years ago. A valid and
reproducible FFQ to measure multiple nutrients intake in older New Zealanders is warranted.
Aim: This study aims to assess the validity and reproducibility of an FFQ designed to
measure a range of relative nutrient intakes in older adults aged 65 to 74 years in New
Methods: As part of the Researching Eating, Activity and Cognitive Health (REACH) study,
a convenience sample of community-dwelling older adults 65 to 74 years were recruited for a
cross-sectional observational study. Participants (n = 166) who completed a 109-item FFQ to
assess dietary intakes over the past month and a four-day food record (4DFR) were included
in the validity analysis; participants (n = 319) who completed the FFQ and re-administered
FFQ four weeks later were included in the reproducibility analysis. Energy intake was
adjusted for nutrients in the statistical methods. Relative validity and reproducibility of the
FFQ were assessed using paired t-tests, Pearson’ or Spearman’s correlation coefficients,
cross-classification with weighted kappa statistics, Bland-Altman plots, and linear regression
analysis for energy and 28 nutrients.
Results: Energy adjustment caused moderate improvements on both validity and
reproducibility. The validity correlations for energy adjusted nutrient intakes ranged from
0.05 (selenium) to 0.76 (alcohol), with a mean of 0.35. Validity correlations above 0.40 were
observed for 12 nutrients after energy adjustment, including carbohydrate, sugar, dietary
fibre, total fat, monounsaturated fat, polyunsaturated fat, cholesterol, vitamin E, calcium, and
magnesium. At least 50% of participants were correctly classified into the same tertiles for
nine nutrients. Less than 10% of participants were grossly misclassified into the opposite
tertiles for seven nutrients. Weighted kappa values for validity demonstrated fair agreement
(ĸ 0.21-0.40) for 19 nutrients and good agreement (ĸ >0.61) for alcohol intake.
Reproducibility correlations for energy adjusted nutrients ranged from 0.30 (vitamin A) to
0.91 (alcohol), with most nutrients (n = 25) falling between 0.60 and 0.80. For
reproducibility, the mean correct classification was 60%, ranged between 53 and 78%. Gross
misclassification for energy adjusted nutrients ranged from 0.6 to 7.8%. Weighted kappa
values for reproducibility demonstrated moderate agreements (ĸ 0.41-0.60) for 25 energy
adjusted nutrients and good agreement (ĸ >0.61) for alcohol.
Conclusion: The FFQ showed reasonable relative validity for ranking nutrient intakes in
older New Zealanders 65-74 years old. The FFQ appears to have good reproducibility for
assessing energy and nutrient intakes. The FFQ could be used in future research for relative
nutrient assessments in older adults but is not suitable for measuring absolute nutrient intakes.