PILOT PHASE STUDIES ON THE ACCURACY OF DIETARY-INTAKE MEASUREMENTS INTHE EPIC PROJECT - OVERALL EVALUATION OF RESULTS

Background. As part of the European Prospective Investigation into Can cer and Nutrition (EPIC), preliminary studies were conducted to evalua te the accuracy of individuals' dietary intake measurements from newly developed questionnaires. Methods. In six countries that adhered from the very beginning to the multicentre, cc-ordinated EPIC project, the validity studies were based on two repeal questionnaire measurements at the start and at the end of a 1-year period, in groups of about 100 volunteers of both sexes. In addition, during this year, up to 12 24- hour recalls per parson were taken monthly, and up to four blood and u rine specimens were collected for measurement of biochemical markers. In three countries that joined EPIC later, the designs of the validity studies and type of 'reference' measurement chosen were somewhat diff erent. The results presented in this overview paper are taken partly f rom more detailed, country-specific publications, and partly from a ce ntral (re-)analysis of the original data, to ensure a uniform approach to the statistical analyses and presentation. Results, averaged over subgroups by country and gender, Spearman coefficients of correlation between questionnaire measurements and the individuals' average 24-hou r recalls ranged from 0.37 for fish to 0.68 far dairy products and 0.7 9 for alcoholic beverages. For energy-adjusted nutrient intakes (or nu trient densities, in the UK), mean Pearson correlation coefficients, c orrected for residual attenuation due to day-to-day variations in the 24-hour recalls in all but two countries, ranged from 0.37 for retino[ and 0.48 for vitamin E to 0.60 for carbohydrates and 0.12 for total a lcohol intake. Correlations between energy-adjusted nutrient intakes a nd biochemical markers on average were low, but varied considerably be tween study centres. Conclusions. On average, most estimated correlati on coefficients were of similar magnitude to those observed by indepen dent research groups. The role of the preliminary validity studies, an d various benefits drawn from these studies for further planning of th e EPIC project are discussed.