Quality control of nutrient data entry for a long-term, multi-centre dietary intervention trial

The Diet and Breast Cancer Prevention Study is a multi-centre, randomized intervention trial to determine if a low-fat, high-carbohydrate diet would reduce the incidence of breast cancer in women at increased risk for the disease. The study began in 1988 and was completed in December 2005. We recruited 4690 women from 5 cities across Canada and asked them to provide 3-day food records at each clinic visit. We analyzed 82,000 food records using Nutrition Data System from the Nutrition Coordinating Centre, University of Minnesota. Our quality control program needed to maximize accuracy and consistency despite a large staff in various locations, changes to the NDS that excluded Canadian foods and an astounding number of new food products. We screened prospective staff to assess their food knowledge and provided extensive training and continuing education. We compiled a supplementary database of new product information and data entry rules. Records with energy and fat intakes beyond usual thresholds were checked. Inter-dietitian variation was assessed by re-entering a sample of food records and achieved a correlation of greater than 0.9 for all macronutrients. This is the only study of diet and breast cancer prevention to collect food records and blood samples over a prolonged period. High quality nutrient data allows us to examine diet and breast cancer risk and phenotype.