title: Relative validity of the food frequency questionnaire used to assess dietary intake in the Leiden Longevity Study.
abstract: BACKGROUND
  Invalid information on dietary intake may lead to false diet-disease associations. This study was conducted to examine the relative validity of the food frequency questionnaire (FFQ) used to assess dietary intake in the Leiden Longevity Study.
  
  
  METHODS
  A total of 128 men and women participating in the Leiden Longevity Study were included in the present validation study. The performance of the FFQ was evaluated using the mean of three 24-hour recalls as the reference method. Evaluation in estimating dietary intake at the group level was done by paired t-tests. The relative validity of the individual energy adjusted level of intake was assessed with correlation analyses (Pearson's), with correction for measurement error.
  
  
  RESULTS
  On group level, the FFQ overestimated as well as underestimated absolute intake of various nutrients and foods. The Bland and Altman plot for total energy intake showed that the agreement between the FFQ and the 24-hour recalls was dependent of intake level. Pearson correlation coefficients ranged from 0.21 (alpha linolenic acid) to 0.78 (ethanol) for nutrients and from -0.02 (legumes, non-significant) to 0.78 (alcoholic beverages) for foods. Adjustment for energy intake slightly lowered the correlation coefficients for nutrients (mean coefficient: 0.48 versus 0.50), while adjustment for within-subject variation in the 24-h recalls resulted in higher correlation coefficients for both nutrients and foods (mean coefficient: 0.69 for nutrients and 0.65 for foods).
  
  
  CONCLUSIONS
  For most nutrients and foods, the ability of the FFQ to rank subjects was acceptable to good.
authors.affiliation: Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands. Martinette.Streppel@wur.nl
authors.forename: Martinette T
authors.initials: MT
authors.lastname: Streppel
authors.forename: Jeanne H M
authors.initials: JH
authors.lastname: de Vries
authors.forename: Saskia
authors.initials: S
authors.lastname: Meijboom
authors.forename: Marian
authors.initials: M
authors.lastname: Beekman
authors.forename: Anton J M
authors.initials: AJ
authors.lastname: de Craen
authors.forename: P Eline
authors.initials: PE
authors.lastname: Slagboom
authors.forename: Edith J M
authors.initials: EJ
authors.lastname: Feskens
mesh_terms: D000368:Aged; D004034:Diet Surveys; D002149:Energy Intake; D005247:Feeding Behavior; D005260:Female; D006801:Humans; D016014:Linear Models; D008136:Longevity; D008297:Male; D011939:Mental Recall; D008875:Middle Aged; D009426:Netherlands; D015596:Nutrition Assessment; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires