Specific hypotheses tested included an adverse effect of saturated fat and carotenoids (alpha-carotene, lutein, and lycopene), flavonoids, folic acid, and vitamin B6. Plausible biological interactions between nutrients, such as fatty acids of the n-6 and n-3 series were also explored. Each participating center sent data on tape to the coordinating unit at the Department of Nutrition, Harvard School of Public Health. The relations of dietary factors and coronary heart disease were first estimated within each study and compared for consistency. Data were then combined to obtain the best overall estimates, taking into account the validity of dietary data collected at each center. Members from study centers met annually to discuss the interpretation of findings. Over 6,000 cases of myocardial infarction or coronary death were anticipated, which should have provided excellent precision in measuring associations, and allowed the comparison of extreme intakes that were poorly represented in individual studies.