THE IMPLICATIONS OF UNDERREPORTING IN DIETARY STUDIES

Dietary data from the Western Sydney Dietary Survey 1989-90 (n = 512) was used to investigate: 1. the prevalence and predictors of underrepo rting of energy intake, 2. the effects on results of excluding data fr om underreporters for analysis of mean nutrient intakes, and 3. the pr oportion of energy intake supplied by macronutrients and proportions o f subjects who met dietary goals. The proportion whose measured energy intakes from a Food Frequency Questionnaire (FFQ) were below cut-poin ts for biologic plausibility was 28.5 per cent; it was higher for subj ects who had BMI > 25 and were female. Point estimates for mean intake s of energy and nutrients were all greater when data from underreporte rs were excluded, but nutrient intakes expressed as percentages of ene rgy intake remained largely unchanged. Increases in estimated mean pop ulation intake for each nutrient ranged from 7 per cent to 14 per cent for males, and 12 per cent to 17 per cent for females. Estimates of t he percentages of the sample who did not meet dietary goals were signi ficantly lower for a number of nutrients when underreporters were excl uded. We conclude that: 1. results expressed as a percentage of energy intake are not affected by the exclusion of energy underreporters, an d 2. estimates of the proportion of populations meeting some nutrient goals and associations between diet and disease are likely to change m eaningfully and significantly with the exclusion of data from underrep orters.