What type of studies are the IA and AA studies?

The IA and AA studies are observational, retrospective cohort studies. They make use of data from actual/real health examinations, rather than setting up a trial in which people are randomly assigned to a particular procedure or protocol. Observational studies can evaluate risk factors for disease which are then statistically analysed to answer a pre-specified research question. Because the IA and AA studies collect information on procedures that have already happened, they are called ‘retrospective’ studies.