Data analysis and interpretation: making associations between exposure and disease in cohort studies

If the investigator knows the exact time that each participant was at risk, it is possible to calculate the incidence rate. Incidence rates can be compared between different groups within a population in the same way as prevalence rates can, that is using standard statistical tests, and/or, (perhaps more appropriately) comparing 95% CI between two groups in a population. Another valuable tool that can be used to highlight possible associations between disease outcome and risk factor exposure is the calculation of relative risk.