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| Domain of bias | Description |
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| Preintervention |
| Bias due to confounding | Baseline confounding. When one or more preintervention prognostic factors predict the intervention received at baseline (start of follow-up) |
| Time-varying confounding. When the intervention received can change over time and when postintervention prognostic factors affect the intervention received after baseline |
| Bias in selecting participants for study | When selection of participants is related to both intervention and outcome |
| Lead time bias. When some follow-up time is excluded from the analysis |
| Immortal time bias. When the interventions are defined in such a way that there is a period of follow-up during which the outcome cannot occur |
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| At intervention |
| Bias in classifying interventions | When intervention status is misclassified |
| Nondifferential misclassification. Is unrelated to the outcome |
| Differential misclassification. Is related to the outcome or to the risk of the outcome |
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| Postintervention |
| Bias due to deviating from intended intervention | When there are systematic differences between intervention and comparator groups in the care provided |
| Bias due to missing data | When attrition (loss to follow-up), missed appointments, incomplete data collection, and exclusion of participants from analysis by primary investigators occur |
| Bias in measuring outcomes | When outcomes are misclassified or measured with error |
| Nondifferential measurement error. Is unrelated to the intervention received; it can be systematic or random |
| Bias in selecting reported result | Selective reporting of results that should be sufficiently reported to allow the estimate to be included in a meta-analysis (or other synthesis) is considered. When selective reporting is based on the direction, magnitude, or statistical significance of intervention effect estimates. Selective outcome reporting. When the effect estimate for an outcome measurement was selected from among analyses of multiple outcome measurements for the outcome domain. Selective analysis reporting. When results are selected from intervention effects estimated in multiple ways |
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| Judgment for each domain |
| Low RoB | Study is comparable to a well-performed, randomized trial with regard to this domain |
| Moderate RoB | Study is sound for a nonrandomized study with regard to this domain but cannot be considered comparable to a well-performed, randomized trial |
| Serious RoB | Study has some important problems in this domain |
| Critical RoB | Study is too problematic in this domain to provide any useful evidence on the effects of intervention |
| No information | No information on which to base a judgment about risk of bias for this domain |
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| Overall judgment |
| Low RoB | Study is judged to be at low risk of bias for all domains |
| Moderate RoB | Study is judged to be at low or moderate risk of bias for all domains |
| Serious RoB | Study is judged to be at serious risk of bias in at least one domain, but not at critical risk of bias in any domain |
| Critical RoB | Study is judged to be at critical risk of bias in at least one domain |
| No information | No clear indication that the study is at serious or critical risk of bias, and there is a lack of information in one or more key domains of bias (a judgment is required for this) |
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