This is a blog describing the concepts of odds ratio and relative risk. Both are two distinct terms used to denote “strength of association”, i.e. the extent to which a particular factor is associated with the disease/condition under study. For example, “smokers have 6 times increased risk of getting lung cancer than non-smokers”, here the value “6” denotes the strength of causal association between smoking and lung cancer. The blog explains that odds ratio is a (rough) measure of strength of association between risk factor and outcome/disease in a case control study. It is defined as the ratio of the odds of an event occurring in one group to the odds of it occurring in another group.

The blog goes on to explain that relative risk is the ratio between incidence of outcome/disease among exposed people and that among unexposed people. It is usually used in a cohort study where there is a definite population under study and we can calculate incidence rates.

The blog also includes the formulas to calculate both odds ratios and relative risk. Read the blog

Students 4 Best Evidence (S4BE) is a growing network of students from around the world, from school age to university, who are interested in learning more about evidence-based healthcare (EBH). The network is supported by the UK Cochrane Centre. In addition to the website, the S4BE has a Facebook group and Twitter feed. For more information, read Selena Ryan-Vigs blog which introduces Students 4 Best Evidence.

GET-IT provides plain language definitions of health research terms

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