A risk ratio is a good measure to use for a metaanalysis if you have data from longitudinal cohorts or clinical trials. For studies that already reported odds ratios, the meta analysis results were used exactly as reported in the. The basic difference is that the odds ratio is a ratio of two odds yep, its that obvious whereas the relative risk is a ratio of two probabilities. Education level was a key determinant, with lower levels associated with higher odds of depression or 6. How to convert odds ratios to relative risks rbloggers. In some sense the relative risk is a more intuitive measure of effect size. To show that while two odds ratios can be calculated in a pairmatched study, there is only one relative risk for such design, and to discuss the implications for meta analysis involving both paired and unpaired binary data. The risk ratio or relative risk is the ratio of the risk of an event in the two groups, whereas the odds ratio is the ratio of the odds of an event see box 9.
I am doing a meta analysis of studies which reported their estimates sometimes as or and sometimes as rr. Choosing effect measures and computing estimates of. Nccmt ure forest plots understanding a metaanalysis. The black squares represent the odds ratios of the individual studies, and the horizontal lines their 95 % confidence intervals. The results are variously presented as odds ratios, hazard ratios, relative risk and regression beta and coefficient. Rr and or are commonly used measures of association in observational studies. Converting an odds ratio to a range of plausible relative. It is generally thought to be easier to interpret than an odds ratio. The most recent meta analysis in 2011 identified a positive odds ratio of 5. Conveniently, it can be fitted by all modern software for glmms.
Another possibility is metaparm, part of the ssc package parmest, which you can use together with the parmhet package to do meta analyses with heterogeneity tests and varianceweighted geometric mean effects. As for risk ratios and odds ratios, hazard ratios are analysed by taking the log and the results are shown on a logarithmic scale. This paper describes a method to convert metaanalytic results in log odds ratio to either risk. Several standalone software packages dedicated specifically for. The incidence of depression and anxiety in patients with. How do i calculate effect sizes from relative risk, hazard. Impact of cooking oil fume exposure and fume extractor use. Understanding absolute and relative risk reduction. The program combines ease of use with a wide array of computational options and sophisticated graphics. Because you want to analyze the incidence, rr should be used.
We demonstrate the use of sas, stata, and r software for the analysis. Relative risk risk ratio meta analysis menu location. For a short overview of meta analysis in medcalc, see meta analysis. It is important to reiterate that for any of these methods to be valid, the scales or instruments. The difference between relative risk and odds ratios the. When continuous outcomes are measured using different. Assembling data for a metaanalysis of log odds ratios. The relative risk also known as risk ratio rr is the ratio of risk of an event in one group e. Table 3 odds ratios and 95% confidence intervals for cooking timeyears and risk of lung cancer between cases and controls in the taiwan gelac study during 20022010. Unfortunately, in some situations, you just have to get an or, notably logistic regression and retrospective casecontrol studies. Note that the results from statsdirect may differ slightly from other software or from those quoted in papers. Risk ratio rr is a ratio that used to compare the risks incidence for the two groups. As odds ratio and hazard ratio are the approximation to the relative risks, but they could be adjusted in multivariable settings. Individual patient data meta analysis in this kind of meta analysis, we get the raw data from each trial.
How can i choose odds ratio or risk ratio in metaanalysis. We have demonstrated consistent results for shortterm mortality with a narrower confidence interval, supporting the notion that subclinical. The 95% confidence intervals would contain the true underlying effect in 95%. The odds ratio is the ratio of the odds between 2 groups. Metaanalysis of hazard ratios statistical software. The only information i have is the odds ratios and 95% confidence intervals. Algebra and an example, along with standard software for implementing relative risk regression models. The homemade video abstract on the bmj website shows you the difference between odds and risk, and how one odds ratio can mean several different relative risks rrs, depending on the risk in one of the groups. Not all of the described methods have been implemented in the commonly used meta analysis software packages and may require statistical coding. To calculate rr, you should divide the incidence in exposed group by the incidence in the unexposed group. Many metaanalyses use the risk ratio rr and its logarithm because of its simpler interpretation. Literature altman dg 1991 practical statistics for medical research. This meta analysis was conducted to explore the differences between reported rates and provide a pooled estimate of risk for postinfectious irritable bowel syndrome piibs.
The pooled relative risk with 95% ci is given both for the fixed effects model and the random effects model. When should we use a risk ratio, odds ratio and relative. If the value 1 is not within the 95% ci, then the relative risk is statistically significant at the 5% level p odds ratio and rate ratio, and conventional metaanalysis approaches must be used for example, the rate ratio is not compatible with logistic regression, methods that account for the sampling variation in the estimate of the betweenstudy variance e. Combining risk estimates from observational studies with different. Im doing a meta analysis of some studies that report results variously as odds ratios, hazards ratios or rate ratios all with confidence intervals. Nccmt ure forest plots understan ding a metaa nalysis in 5 minutes or less. When the outcome data are available only as studylevel summaries such as odds ratio and rate ratio, and conventional metaanalysis approaches must be used for example, the rate ratio is not compatible with logistic regression, methods that account for the sampling variation in the estimate of the betweenstudy variance e. The odds ratio or is the ratio of odds of an event in one group versus the odds of the event in the other group. When should we use a risk ratio, odds ratio and relative ratio in the metaanalysis to. Comprehensive meta analysis is a powerful computer program for meta analysis. Odds ratio and confidence interval in metaanalysis.
Suppose the goal of a metaanalysis is to aggregate the results from studies contrasting two groups e. Thus, it measures the change in risk of treatment versus control over the followup period. The use of odds ratio or relative risk depends on the design of the study. Odds ratios are a necessary evil in medical research. Stata has a comprehensive set of userwritten commands to perform meta analysis of studies with i binary outcomes i.
For both measures a value of 1 indicates that the estimated effects are the same for both interventions. Conducting metaanalyses in r with the metafor package. By using the odds ratio and the baseline risk, the. This paper provides practical advice for authors and readers on converting odds ratios to relative risks the odds ratio is a common measure in medical research of the effect size comparing two groups treatments or risk. I need to calculate the pooled odds ratio and associated 95% confidence interval for meta analysis of 2 studies about the risk of bleeding. How to conduct a metaanalysis on studies that report. In the example, point estimates and confidence intervals for the overall log odds ratio differ between the conventional and alternative methods, in ways that can affect inferences.
I am conducting metaanalysis for mortality of patients with heart failure. In this video i will discuss how to interpret them and how to apply them to patient care. An approximation is the ratio of the cumulative incidence rates or cir unit is % or casespersons when these rates are less than 10 %. Stata meta analysis of odds ratios 272analytics videos. Metaanalysis of precalculated effect estimates in r or stata.
Learn how to meta analyze odds ratios in stata using metan. How we took adjusted odds ratio for metaanalysis when. We then analyse them like a single, multicentre clinical trial. Several studies identify ibs as a sequela of infectious gastroenteritis ige with reported prevalence ranging from 4% to 31% and relative risk from 2. It is the standard way of risk assessment in cohort studies. How to interpret and use a relative risk and an odds ratio. The summary statistics that are usually used to measure treatment effect include odds ratios or, relative risks rr, and risk differences. Odds and odds ratios have been described in a previous question. Odds ratio meta analysis reversing the reference category. The area of the black squares reflects the weight each trial contributes in the metaanalysis. The 95% confidence intervals would contain the true underlying effect in. The relative risk is a ratio of two incidence rates or two mortality rates. Programming is straightforward in the 3 software packages. Mantelhaenszel test and odds ratio meta analysis menu locations.
One option is network metaanalysis, as discussed in chapter 11. These also have an eform option for when the input estimates and standard errors are for risk ratios, odds ratios or geometric mean ratios. As for the particular topic of combining hazard ratio studies in a meta analysis, the book by parmar and machin 1995 and the paper by parmar et al. Learn about the ttest, the chi square test, the p value and more duration. For example, meta analysis may often be best performed using relative effect measures risk ratios or odds ratio and the results reexpressed using absolute effect measures risk differences or numbers needed to treat see chapter 12, section 12. Postinfectious irritable bowel syndromea metaanalysis. Do the calculations with log odds ratios and report risk. Statistical software such as revman may be used to calculate these ors in this example. How we took adjusted odds ratio for metaanalysis when different studies put it in different ways in relation to explanatory variables. Is there any way to combine these togetherconvert between them so that i can do a meta analysis of all the studies.
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