INDIAN JOURNAL OF COMMUNITY HEALTH / VOL 32 / ISSUE NO 02 / APR - JUN 2020 [Expression and interpretation…] | Sharma SK et al 344 REVIEW ARTICLE Expression and interpretation of relative risk and odds ratio in biomedical research studies Suresh K Sharma 1 , Shiv Kumar Mudgal 2 , Jitender Chaturvedi 3 1 Professor & Principal, College of Nursing; All India Institute of Medical Sciences, Rishikesh-249203 Uttarakhand; 2 Tutor, College of Nursing; All India Institute of Medical Sciences, Rishikesh-249203 Uttarakhand; 3 Assistant Professor, Department of Neurosurgery, All India Institute of Medical Sciences, Rishikesh-249203 Uttarakhand, India Abstract Introduction Methodology Results Conclusion References Citation Tables / Figures Corresponding Author Prof Suresh K Sharma, College of Nursing, All India Institute Of Medical Science, Rishikesh-249203 Uttarakhand, India E Mail ID: skaiims17@gmail.com Citation Sharma SK, Mudgal SK, Chaturvedi J. Expression and interpretation of relative risk and odds ratio in biomedical research studies. Indian J Comm Health. 2020;32(2):344-347. Source of Funding: Nil Conflict of Interest: Nil Article Cycle Received: 30/03/2020; Revision: 15/04/2020; Accepted: 25/05/2020; Published:30/06/2020 This work is licensed under a Creative Commons Attribution 4.0 International License. Abstract Relative risk and odds ratio are commonly used in the biomedical research studies; however, expression and interpretation must be done very carefully. A risk ratio and an odds ratio are used in cohort studies but only odds ratio is used in case control studies. However, relative risk or risk ratio is found to be frequently used in the interventional biomedical research studies. The relative risk and odds ratio provide important information regarding the effect of a risk factor on the outcome of interest. The relative risk and odds ratio of 1 suggests that there is no difference between two groups. A value >1 suggests increase risk, while a value <1 suggest reduction of risk. If the confidence interval meets or includes value 1.00 (line of no difference) indicates there is no difference between the groups. Keywords Biomedical research; odds ratio; risks; relative risk Introduction Many research articles explain their results in terms of relative risk (RR) and odds ratio (OR) to interpret the whether results are significant or not for categorical outcomes such as results of a meta-analysis reported effect of heparin and normal saline to maintain patency of central venous catheter and presented by risk ratio 0.83, 95% CI 0.50 – 1.40; P = 0.13.(1) While, these two widely used terms have been discussed in various articles for a novice researcher it is still difficult to interpret the odds ratio and relative risk. Therefore, in this article authors tried to discuss interpretation of these terms in simple and practical language with examples. Reader may note that the examples given in this article are hypothetical. Relative Risk (RR) The relative risk (RR) is probability of an incident occurrence after exposure to a risk in one group compared with the probability of its occurrence in placebo/other group.(2) Worked Example: Let us start with an assumed example that a researcher conducted a cohort study to assess the risk of infections when emergency craniotomies were performed on patients with intracranial hematoma after road traffic accidents. Researcher presented the data and calculated the relative risk as follow: Presentation of the data in a 2x2 contingency (Table 1) helps the readers in analyzing and interpretation of results. In table 1 it is clear that emergency craniotomy was undertaken in a total of 139 patients and eleven out of them got infections, then calculation of cumulative incidence by 11 divided by 139, or 7.91%. In the same way the cumulative incidence calculated in the patient for those who had not undergone an emergency craniotomy were 2 divided by 98 or 2.04%. Therefore, the risk ratio is 7.91/2.04 or 3.8. When we are interpreting the results of the above study, we say that individuals who had undergone emergency craniotomy had 3.8 times the risk of infection compared to those who did not undergo emergency craniotomy.(2)