Examining and Comparing the Validity and Reproducibility of Scales to Determine the Variety of Vegetables Consumed: Validation Study

Abstract

Background Previous studies have reported that vegetable variety reduces the risk for noncommunicable diseases independent of the amount consumed. Objective This study aimed to examine and compare the validity and reproducibility of several scales to determine vegetable variety. Methods In total, 23 nutrition students in Japan reported their vegetable intake over the past month using a self-administered questionnaire between July and August 2021. Specifically, four scales were used: (1) a single question regarding the number of vegetables consumed (scale A); (2) a scale containing 9 vegetable subgroups included in the brief-type self-administered diet history questionnaire (scale B); (3) a scale containing 19 vegetable items included in a self-administered diet history questionnaire (scale C); and (4) a scale containing 20 vegetable items from the Ranking of Vegetable Consumers in Japan, which was analyzed based on a report on the National Health and Nutrition Survey in Japan (scale D). Scale validity was assessed by correlation with the number of vegetables consumed, which was collected from dietary records for 7 consecutive days. Reproducibility was assessed by test-retest reliability. Results Regarding the validity of the 4 scales, significant correlations were found between scales C (ρ=0.51) and D (ρ=0.44) with vegetable variety based on dietary records, but scales A (ρ=0.28) and B (ρ=0.22) were not significantly correlated. Reproducibility showed a significant correlation in scale B (ρ=0.45) and strong correlations in scales C (ρ=0.73) and D (ρ=0.75). Conclusions The scales for vegetable items have acceptable validity and reproducibility compared to the scales that used a single question or vegetable subgroup and, therefore, may determine the variety of vegetables consumed.