title: Response rates with different distribution methods and reward, and reproducibility of a quantitative food frequency questionnaire.
abstract: OBJECTIVE
  To evaluate the use of a self-administered quantitative food frequency questionnaire (QFFQ) in a national dietary survey concerning (a) response rates with different distribution methods and reward; (b) degree of underreporting of energy intake; (c) reproducibility of the QFFQ; and (d) seasonal variation on reported intake.
  
  
  METHODS
  A pilot study was performed in 1992 to test response rates to the QFFQ with three different distribution methods, with and without reward, in a random sample of 1200 adults aged 16-79 y. In another study, the QFFQ was distributed to a nation-wide, representative random sample of 5008 adults aged 16-79 y during June, September, November 1993 and March 1994. Reproducibility was evaluated among 90 responders to the survey who answered another QFFQ six weeks later.
  
  
  RESULTS
  The distribution method combining postal distribution and collecting the QFFQ by interviewer as well as an offer to participate in a lottery, gave the highest response rate (72%). The possibility to get a reward increased the response rate by 9, 14 and 57%, respectively, depending on the distribution method used. The mean daily energy intake and the percentage of subjects claiming to have unlikely low energy intake did not differ significantly between the different ways of distribution. In the main survey the mean ratio between energy intake and estimated basal metabolic rate was 1.58 among men and 1.47 among women, and 37% of men and 45% of women had a ratio below 1.35. Spearman rank correlations between the two QFFQ ranged from 0.48 (edible fats) to 0.91 (coffee) with a median coefficient of 0.70. For nutrients correlations ranged from 0.55 (carbohydrate E%) to 0.81 (alcohol), with a median coefficient of 0.72. The season of questionnaire administration was of minor importance for the reported intake of the main foods and nutrients.
  
  
  CONCLUSIONS
  The QFFQ-method is suitable for use in a Norwegian nutritional surveillance system.
  
  
  BACKGROUND
  National Nutrition Council, Ministry for Agriculture, Ministry for Health and Social Affairs and Norwegian Research Council.
authors.affiliation: National Nutrition Council, Institute for Nutrition Research, University of Oslo, Norway.
authors.forename: L
authors.initials: L
authors.lastname: Johansson
authors.forename: K
authors.initials: K
authors.lastname: Solvoll
authors.forename: S
authors.initials: S
authors.lastname: Opdahl
authors.forename: G E
authors.initials: GE
authors.lastname: Bjørneboe
authors.forename: C A
authors.initials: CA
authors.lastname: Drevon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003069:Coffee; D015930:Diet Records; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D004041:Dietary Fats / Q000008:administration & dosage; D002149:Energy Intake; D005260:Female; D005502:Food; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway; D010865:Pilot Projects; D015203:Reproducibility of Results; D012201:Reward; D012621:Seasons; D011795:Surveys and Questionnaires
chemical_list: D003069:Coffee; D004040:Dietary Carbohydrates; D004041:Dietary Fats