Fig. 3

The full ER diagram shows the relationships among the different entities in the database. Each box symbolised a single entity corresponding to an Epi Info form, except the ARM and CONTRAST, which were constructed as grids (i.e. table-like data entry fields) and added to the main form. The data items were listed within each entity. The lines with ‘1’ and ‘M’ markings show the 1:M relationships among the entities. The primary and foreign keys are indicated as GlobalRecordId and FKEY in Epi Info, respectively