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*Well, both measure association between a binary outcome variable and a continuous or binary predictor variable.*

- Relative risks and odds ratios: What’s the difference?
- When to use the odds ratio or the relative risk?
- Lesson 3: Measures of Risk

## Relative risks and odds ratios: What’s the difference?

In biomedical research, we are often interested in quantifying the relationship between an exposure and an outcome. In this article, which is the fourth in the series of common pitfalls in statistical analysis, we explain the meaning of risk and odds and the difference between the two. Researchers are often interested in evaluating the association between an exposure and an outcome. At first glance, though these two concepts seem similar and interchangeable, there are important differences that dictate where the use of either of these is appropriate. A randomized trial of sclerotherapy versus ligation for esophageal varices hypothetical data. In the example above, for the same data set, the chances of death appear markedly different when expressed as risks and odds.

The relative risk RR or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio , relative risk measures the association between the exposure and the outcome. Relative risk is used in the statistical analysis of the data of ecological , cohort , medical and intervention studies, to estimate the strength of the association between exposures treatments or risk factors and outcomes. For example, in a study examining the effect of the drug apixaban on the occurrence of thromboembolism, 8. Assuming the causal effect between the exposure and the outcome, values of RR can be interpreted as follows: [2]. Relative risk is commonly used to present the results of randomized controlled trials.

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## When to use the odds ratio or the relative risk?

This is a preview of subscription content, access via your institution. Rent this article via DeepDyve. Correspondence to Carsten Oliver Schmidt. Reprints and Permissions. Schmidt, C. When to use the odds ratio or the relative risk?.

A retrospective cohort study evaluated the association between type of ventilatory support and mortality among adult patients with interstitial lung disease and acute respiratory failure. In our example, we calculated the OR and RR to answer the study question. It is important to understand the difference between these two statistical methods for calculating risk, which one is more applicable to answer this research question, and how they are interpreted. The OR is defined as the ratio of odds of an event occurring, estimated by calculating the ratio of the number of times that the event of interest occurs to the number of times that it does not ratio of events to non-events between exposed and unexposed groups. That statement is easily interpreted because it deals with probabilities which range from 0 to 1.

Some studies use relative risks RRs to describe results; others use odds ratios ORs. Both are calculated from simple 2x2 tables. The question of which statistic to use is subtle but very important. Probability is the likelihood of an event in relation to all possible events. Relative risk is a ratio of probabilities. It compares the incidence or risk of an event among those with a specific exposure with those who were not exposed eg, myocardial infarctions in those who smoke cigarettes compared with those who do not Figure. It is only appropriate, therefore, to use RR for prospective cohort studies.

## Lesson 3: Measures of Risk

What are relative risk, number needed to treat and odds ratio? Risk difference RD is the difference in risk of the outcome event between control and experimental group. Control group is not exposed to the intervention, whereas experimental group is the one that is exposed to intervention. The risk of outcome event in the control group is also called baseline risk. The NNT is the inverse of the risk difference and indicates the number of patients required to be treated to avoid one additional outcome event.

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Understanding Relative Risk, Odds Ratio, and Related Terms: As Simple as categorical outcomes) such as relative risks and odds ratios It is estimated as the difference in the absolute downloads/yes/_MODULE_pdf. Accessed.

The key to epidemiologic analysis is comparison.