Odds Ratio (OR) and Its Use
The odds ratio can be defined as the ratio of the odds of an event in one group versus the odds of an event in the other group (Ranganathan, Aggarwal, & Pramesh, 2015). For example, an odds ratio of an event in the treatment group versus the odds of an event in the control group. Odds ratios are used to provide a comparison of the relative odds of the occurrence of an outcome when it is exposed to a variable of interest (Ranganathan et al., 2015). The odds ratio can also be used to identify whether a certain exposure is a risk factor for a particular outcome. The odd ratio also provides insight into the extent of certain risk factors to an outcome.
Risk Ratio (RR) and Its Use
RR is the ratio of the risk of an event in one group compared to the risk of the event in another group (Ranganathan et al., 2015). For example, the risk of an event in an exposed group versus the risk of an event in the non-exposed group. RR is used to provide information on the risk of a health event in one group with the risk in another group (Ranganathan et al., 2015). An RR of 1.0 shows that there is no difference in risk between the two groups while an RR of more than 1.0 shows a high risk among the exposed group.
Comparison and Contrast of RR and OR
One of the differences between OR and RR is that for RR the true incidence rate must be present for it to be used in a study (Viera, 2008). Another difference is that OR is used for rare or uncommon diseases because it is difficult to create exposed and non-exposed groups in such cases. OR can be viewed as the probability of an event versus the probability of a non-event whereas RR can be viewed as the probability of an event occurring versus the probability of an event not occurring (Viera, 2008). In multiple sample inferences OR can provide a reasonable approximation of the RR (Rosner, 2021). In cases where the outcome is common, the OR can provide an exaggerated estimation of the RR (Viera, 2008). Both OR and RR provide information on the change in how likely an outcome is likely to happen. However, the two use different methods to provide this information.
Advantages and Disadvantages of OR
One of the advantages of OR is that it is simple to calculate and easy to interpret (Ranganathan et al., 2015). This ensures that researchers can identify results with which decisions can be made. Another advantage is that it helps clinicians to provide patients with more information which can help patients understand the odds of an outcome versus another. The disadvantage of OR is that the odd ratio does not provide accurate results when the initial risk is high (Ranganathan et al., 2015). This can result in misleading interpretations which can affect the results of the study.
Advantages and Disadvantages of RR
Risk ratios are easy to interpret and provide consistent results which are helpful for researchers in clinical studies. RR provides useful interpretations when identifying the probability of an event happening versus the probability of an event not happening (Ranganathan et al., 2015). Also, risk ratios have a mathematical property called collapsibility which ensures that if adjustments are made the size of the risk ratio will not change (Rosner, 2021). One of the disadvantages of risk ratios is that they lack symmetry which means that each outcome has to be represented by its risk ratio.
References
Ranganathan, P., Aggarwal, R., & Pramesh, C. S. (2015). Common pitfalls in statistical analysis: Odds versus risk. Perspectives in Clinical Research. 6(4), 222.
Rosner, B. (2021). Estimation of the Mean of a Distribution. In Fundamentals of Biostatistics (8th ed.). Cengage Learning, Inc.
Viera, A. J. (2008). Odds ratios and risk ratios: What’s the difference and why does it matter? Southern Medical Journal. 101(7), 730-734.