Table measuring risk, rate and odds ratio

Cohort studies allow for directly measuring risk or rate of disease occurrence and their related ratio in subgroups of a population (exposed and unexposed). Case-control studies do not allow the measurement of risk or rates. They, however, allow the estimation of the risk ratio and the rate ratio. The selection of the control group is a crucial step of the study. The following table summarises the type of measures and control selection as described in the above chapter.

Measuring risk, rate and odds ratios in a case-control study, using various sampling methods for controls (Source: Rodrigues L et al. Int J Epidemiol. 1990;19:205-13)

Measure	Definition	Case Control Formulation	Design	Controls sampled from
					1-Risk ratio	form1	form2	Case cohort	Total study population present at the beginning of the study
					2-Rate ratio (incidence density ratio)	form 3	dform4	Density case-control	People at risk at the time of case disease onset
3-Odds ratio	form5	form6	Traditional case-control	People disease free throughout the study period