Estimating relative risks and risk differences in randomised controlled trials: a systematic review of current practice
Abstract Background Guidelines for randomised controlled trials (RCTs) recommend reporting relative and absolute measures of effect for binary outcomes while adjusting for covariates. There are a number of different ways covariate-adjusted relative risks and risk differences can be estimated. Object...
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2025-01-01
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| Online Access: | https://doi.org/10.1186/s13063-024-08690-w |
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| author | Jacqueline Thompson Samuel I. Watson Lee Middleton Karla Hemming |
| author_facet | Jacqueline Thompson Samuel I. Watson Lee Middleton Karla Hemming |
| author_sort | Jacqueline Thompson |
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| description | Abstract Background Guidelines for randomised controlled trials (RCTs) recommend reporting relative and absolute measures of effect for binary outcomes while adjusting for covariates. There are a number of different ways covariate-adjusted relative risks and risk differences can be estimated. Objectives Our goal was to identify methods used to estimate covariate-adjusted relative risk and risk differences in RCTs published in high-impact journals with binary outcomes. Other secondary objectives included the identification of how covariates are chosen for adjustment and whether covariate adjustment results in an increase in statistical precision in practice. Methods We included two-arm parallel RCTs published in JAMA, NEJM, Lancet, or the BMJ between January 1, 2018, and March 11, 2023, reporting relative risks or risk differences as a summary measure for a binary primary outcome. The search was conducted in Ovid-MEDLINE. Results Of the 308 RCTs identified, around half (49%; 95% CI: 43–54%) reported a covariate-adjusted relative risk or risk difference. Of these, 82 reported an adjusted relative risk. When the reporting was clear (n = 65, 79%), the log-binomial model (used in 65% of studies; 95% CI: 52–76%) and modified Poisson (29%; 95% CI: 19–42%) were most commonly used. Of the 92 studies that reported an adjusted risk difference, when the reporting was clear (n = 56, 61%), the binomial model (used in 48% of studies; 95% CI: 35–62%) and marginal standardisation (21%; 95% CI: 12–35%) were the common approaches used. Conclusions Approximately half of the RCTs report either a covariate-adjusted relative risk or risk difference. Many RCTs lack adequate details on the methods used to estimate covariate-adjusted effects. Of those that do report the approaches used, the binomial model, modified Poisson and to a lesser extent marginal standardisation are the approaches used. |
| format | Article |
| id | doaj-art-502d81beb7cf43c9ba0962bdaa966828 |
| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
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| spelling | doaj-art-502d81beb7cf43c9ba0962bdaa9668282025-01-05T12:45:15ZengBMCTrials1745-62152025-01-0126111410.1186/s13063-024-08690-wEstimating relative risks and risk differences in randomised controlled trials: a systematic review of current practiceJacqueline Thompson0Samuel I. Watson1Lee Middleton2Karla Hemming3Department of Applied Health Sciences, College of Medicine and Health, University of BirminghamDepartment of Applied Health Sciences, College of Medicine and Health, University of BirminghamDepartment of Applied Health Sciences, College of Medicine and Health, University of BirminghamDepartment of Applied Health Sciences, College of Medicine and Health, University of BirminghamAbstract Background Guidelines for randomised controlled trials (RCTs) recommend reporting relative and absolute measures of effect for binary outcomes while adjusting for covariates. There are a number of different ways covariate-adjusted relative risks and risk differences can be estimated. Objectives Our goal was to identify methods used to estimate covariate-adjusted relative risk and risk differences in RCTs published in high-impact journals with binary outcomes. Other secondary objectives included the identification of how covariates are chosen for adjustment and whether covariate adjustment results in an increase in statistical precision in practice. Methods We included two-arm parallel RCTs published in JAMA, NEJM, Lancet, or the BMJ between January 1, 2018, and March 11, 2023, reporting relative risks or risk differences as a summary measure for a binary primary outcome. The search was conducted in Ovid-MEDLINE. Results Of the 308 RCTs identified, around half (49%; 95% CI: 43–54%) reported a covariate-adjusted relative risk or risk difference. Of these, 82 reported an adjusted relative risk. When the reporting was clear (n = 65, 79%), the log-binomial model (used in 65% of studies; 95% CI: 52–76%) and modified Poisson (29%; 95% CI: 19–42%) were most commonly used. Of the 92 studies that reported an adjusted risk difference, when the reporting was clear (n = 56, 61%), the binomial model (used in 48% of studies; 95% CI: 35–62%) and marginal standardisation (21%; 95% CI: 12–35%) were the common approaches used. Conclusions Approximately half of the RCTs report either a covariate-adjusted relative risk or risk difference. Many RCTs lack adequate details on the methods used to estimate covariate-adjusted effects. Of those that do report the approaches used, the binomial model, modified Poisson and to a lesser extent marginal standardisation are the approaches used.https://doi.org/10.1186/s13063-024-08690-wBinary outcomesRelative riskRisk differenceCovariate adjustmentStatistical efficiencyStatistical practice |
| spellingShingle | Jacqueline Thompson Samuel I. Watson Lee Middleton Karla Hemming Estimating relative risks and risk differences in randomised controlled trials: a systematic review of current practice Trials Binary outcomes Relative risk Risk difference Covariate adjustment Statistical efficiency Statistical practice |
| title | Estimating relative risks and risk differences in randomised controlled trials: a systematic review of current practice |
| title_full | Estimating relative risks and risk differences in randomised controlled trials: a systematic review of current practice |
| title_fullStr | Estimating relative risks and risk differences in randomised controlled trials: a systematic review of current practice |
| title_full_unstemmed | Estimating relative risks and risk differences in randomised controlled trials: a systematic review of current practice |
| title_short | Estimating relative risks and risk differences in randomised controlled trials: a systematic review of current practice |
| title_sort | estimating relative risks and risk differences in randomised controlled trials a systematic review of current practice |
| topic | Binary outcomes Relative risk Risk difference Covariate adjustment Statistical efficiency Statistical practice |
| url | https://doi.org/10.1186/s13063-024-08690-w |
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