title: The effect of personal characteristics on the validity of nutrient intake estimates using a food-frequency questionnaire.
abstract: OBJECTIVE
  To assess validity of the Nambour food-frequency questionnaire (FFQ) relative to weighed food records (WFRs), and the extent to which selected demographic, anthropometric and social characteristics explain differences between the two dietary methods.
  
  
  METHODS
  Inter-method validity study; 129-item FFQ vs. 12 days of WFR over 12 months.
  
  
  METHODS
  Community-based Nambour Skin Cancer Prevention Trial.
  
  
  METHODS
  One hundred and fifteen of 168 randomly selected participants in the trial (68% acceptance rate) aged 25-75 years.
  
  
  RESULTS
  Spearman correlations between intakes from the two methods ranged from 0.18 to 0.71 for energy-adjusted values. Differences between FFQ and WFR regressed on personal characteristics were significantly associated with at least one characteristic for 16 of the 21 nutrients. Sex was significantly associated with differences for nine nutrients; body mass index (BMI), presence of any medical condition and age were each significantly associated with differences for three to six nutrients; use of dietary supplements and occupation were associated with differences for one nutrient each. There was no consistency in the direction of the significant associations. Regression models explained from 7% (riboflavin) to 27% (saturated fat) of variation in differences in intakes.
  
  
  CONCLUSIONS
  The relative validity of FFQ estimates for many nutrients is quite different for males than for females. Age, BMI, medical condition and level of intake were also associated with relative validity for some nutrients, resulting in the need to adjust intakes estimates for these in modelling diet-disease relationships. Estimates for cholesterol, beta-carotene equivalents, retinol equivalents, thiamine, riboflavin and calcium would not benefit from this.
authors: Queensland Institute of Medical Research, Herston, Queensland 4029, Australia. g.marks@sph.uq.edu.au
authors: Geoffrey C
authors: GC
authors: Marks
authors: Maria Celia
authors: MC
authors: Hughes
authors: Jolieke C
authors: JC
authors: van der Pols