REPRODUCIBILITY AND RELATIVE VALIDITY OF A SELF-ADMINISTERED SEMIQUANTITATIVE FOOD FREQUENCY QUESTIONNAIRE APPLIED TO YOUNGER WOMEN

We have evaluated the reproducibility and relative validity of a semiq uantitative food frequency questionnaire (FFQ) used in a prospective s tudy of risk factors for cervical neoplasia. The questionnaire is a mo dified version of one developed and evaluated in a middle-aged Danish population. In the present study, 122 women from the general populatio n of Copenhagen, aged 20-29 years, completed the FFQ twice at a 1-year interval, and provided three 4-day dietary records during the interve ning year. The mean nutrient intakes calculated from the first and sec ond questionnaire were similar and, for most nutrients, close to those obtained from the dietary records. The Pearson correlation coefficien ts between the mean nutrient intakes from the two questionnaires range d from 0.53 (95% CI, 0.39-0.65) for vitamin E to 0.76 (95% CI, 0.67-0. 83) for vitamin B12 (median, 0.67 [95% CI, 0.56-0.76]). In comparisons between the second FFQ and the dietary records, the correlations rang ed from 0.24 (95% CI, 0.07-0.40) for vitamin D to 0.63 (95% CI, 0.51-0 .73) for sucrose (median, 0.42 [95% CI, 0.26-0.56]). The correlations between FFQ and dietary records were generally higher after adjustment for energy intake (median, 0.53 [95% CI, 0.39-0.65]) and within-perso n variability (median, 0.64 [95% CI, 0.52-0.73]). On average, 71% of t he women were classified in the same (+/- 1) quintile in the second FF Q and the dietary records. An average of 3.8% of the women were grossl y misclassified into the highest and lowest quintiles by the dietary r ecords. The relative validity of the FFQ in this population was simila r to that reported earlier. It is concluded that: the FFQ is reproduci ble and provides a useful scale for categorizing individuals according to their intake of energy and nutrients. (C) 1997 Elsevier Science In c.