Sm. Krebssmith et al., USING FOOD FREQUENCY QUESTIONNAIRES TO ESTIMATE FRUIT AND VEGETABLE INTAKE - ASSOCIATION BETWEEN THE NUMBER OF QUESTIONS AND TOTAL INTAKES, Journal of nutrition education, 27(2), 1995, pp. 80-85
The purpose of this study was to determine how estimates of fruit and
vegetable intake, as determined from food frequency questionnaires, ma
y be affected by the number of foods included. Three different nationa
l surveys of adults were used. Each of the surveys employed a food fre
quency questionnaire, but each included a different number of question
s related to fruits and vegetables. Compared across surveys, values fo
r median frequency of intake of individual fruits and vegetables were
generally similar. However, values for median frequency of total fruit
and vegetable intake, determined by summing across all fruits and veg
etables included in the respective questionnaires, were very different
and were associated with the number of questions asked: the 1987 Nati
onal Health Interview Survey included 20 questions regarding fruits an
d vegetables, and the median frequency of intake was 23.8 times per we
ek; the baseline survey for the national 5 A Day for Better Health Pro
gram included 33 questions, and the median intake was 34.6; and the 19
82-1984 NHANES I Epidemiologic Follow-up Survey included 40 questions,
and the median intake was 38.8. These findings suggest that summing a
cross frequencies for individual foods may not be a valid way to asses
s intakes of total fruits and vegetables. Summary questions and/or adj
ustment factors may need to be employed to increase precision of the e
stimates.