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Validation Information: FFQ (Fruits & Vegetables-Pregnant Women)

Mikkelsen 2007

Relative validity of fruit and vegetable intake estimated by the food frequency questionnaire used in the Danish National Birth Cohort frequency questionnaire used in the Danish National Birth Cohort

Objective: To validate the fruit and vegetable intake estimated from the Food Frequency Questionnaire (FFQ) used in the Danish National Birth Cohort (DNBC). Subjects and setting: The DNBC is a cohort of 101,042 pregnant women in Denmark, who received a FFQ by mail in gestation week 25. A validation study with 88 participants was made. A seven-day weighed food diary (FD) and three different biomarkers were employed as comparison methods.

Results: Significant correlations between FFQ and FD-based estimates were found for fruit (r=0.66); vegetables (r=0.32); juice (r=0.52); fruit and vegetables (F&V) (r=0.57); and fruit, vegetables, and juice (F&V&J) (r=0.62). Sensitivities of correct classification by FFQ into the two lowest and the two highest quintiles of F&V&J intake were 58-67% and 50-74%, respectively, and specificities were 71-79% and 65-83%, respectively. F&V&J intake estimated from the FFQ correlated significantly with urinary flavonoids (r=0.39, p<0.005), plasma b-carotene (r=0.21, p<0.05) and erythrocyte folate (r=0.33, p<0.005); all average biomarker levels increased across increasing quintiles of F&V;J intake.

Conclusion: Data on F&V&J recorded by FFQ in DNBC can be used in etiological analyses of associations between fruit and vegetable intake and health outcomes, provided that the potential misclassification of dietary exposure is kept in mind.

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Validation Information

Year of Publication

Tool Information

Dietary Exposure Measured
Energy, Macronutrient, Food Groups
Tool Type
Food Frequency Questionnaire
Timeframe Tool Measures info
6 months
Portion Size Measures info
Standard portion sizes and recipes were developed for all food items contained on the FFQ
Reporting Method info
Format info
Supplements Measured
Administration Method info
Self administered

Study Information

Study Location
Odense, Denmark
Associated Nutrient Database
Danish food tables
Comparator Validated Against
Biomarkers, Weighed Food Diary


Sample Size
Age of Population

Range: 25-31 years

Female Only
Other Notable Characteristics
Subjects were part of the DNBC (Danish National Birth Cohort) living in Odense, Denmark in weeks 30-31 of their pregnancy.

Total number of nutrients validated: 3 info

Not all of the nutrients validated in the validation studies are included in the table below, as statistical data was only selected to be displayed for a number of nutrients, this included:

  • Energy
  • Fat
  • Saturated Fat
  • Mono-unsaturated Fat
  • Poly-unsaturated Fat
  • Carbohydrates
  • Protein
  • Sugar
  • Non‐starch polysaccharides(NSP)
  • Sodium
  • Calcium
  • Iron
  • Zinc
  • Retinol
  • Folate
  • Folic Acid
  • Vitamin B12
  • Vitamin C
  • Fruit & Vegetables
  • Urinary Nitrogen

To find information on the other validated nutrients please read the validation study.

  • Energy
  • Macronutrients: 3
  • Micronutrients: 0
Comparator Lifestage Sex Nutrient Measured info Mean Difference Standard Deviation info Correlation Coefficient info Cohen's Kappa Coefficient Percentage Agreement Percentage Agreement Categories info Lower Limits of Agreement Upper Limits of Agreement
Weighed Food Diary Adults Female Only Energy (kJ) -1300 (Median) 5
Vegetables (g/d) -26 (Median) 0.29 (S) 5
Biomarkers (urine) Adults Female Only
Biomarkers (plasma) Adults Female Only
Biomarkers (erythrocytes) Adults Female Only

Some results have been calculated using statistical techniques based on the published data.

For further information on statistical terms click on Statistical tests used in validation studies

All correlations coefficients in the table are unadjusted unless stated otherwise. For adjusted correlation coefficients and other statistical methods used in the study e.g. paired t-tests, please read the validation articles.

  • # Adjusted
  • † Energy adjusted.
  • ‡ For loge-transformed, energy-adjusted nutrient intakes.
  • ^ Adjacent included.
  • ᵟ Participants provided identical responses.
  • (w) = Weighted.

Mikkelsen T.N, Olsen S. F, Rasmussen S. E & Olser M. Relative validity of fruit and vegetable intake estimated by the food frequency questionnaire used in the Danish National Birth Cohort. Scandinavian Journal of Public Health (2007) 35 172-179