Norfolk was chosen as our study area because few people in our age group of interest move out of the county, making it easier to follow our participants over a long period of time. Also, Norfolk is served by one general hospital, the Norfolk and Norwich University Hospital NHS Trust. This makes it easier to follow up our participants.
If a study were to be carried out on people diagnosed with cancer or other illnesses, not only might their current diet be affected but also the way they report what they have eaten in the past. Regardless of any diagnosis, it is always difficult for people to describe what they were eating several years ago. A more precise way of examining the effect of diet is to gather a great deal of lifestyle and nutritional information from a very large number of people. As time goes by, repeated dietary information from this group is collected. If anybody in the group develops one of the diseases under investigation, this is recorded. This type of study is called a prospective cohort study. Using this study design, we should be able to observe explicit relationships between dietary and lifestyle factors and risk of disease development.
The original aim was to identify a cohort of 25,000 men and women from the general population of Norfolk. This cohort size was a compromise between the large numbers needed to get enough observations on people who developed cancer or other diseases, and the expense of making detailed measurements on everybody in the cohort. In fact, we recruited over 30,000 people to EPIC-Norfolk at baseline. Cohort studies as large as EPIC are very expensive to set up and run, though the extensive results make all of this worthwhile.