Selection bias | Controlled studies | |
observational studies | Low risk if patients enrolled as consecutively observed based on the pre-existing protocol Low risk if numbers and reasons for exclusions were reported High risk when the association between exposure and outcome is different for study participants compared with non-participants
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Performance bias | Controlled studies | |
Observational studies | |
Detection bias | Controlled studies | |
Observational studies | High risk if there were systematic differences in outcomes assessment among comparison groups High risk if the measurement of exposure is flawed, for example, recall bias in case–control studies
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Reporting bias | Controlled studies | |
Observational studies | |
Confounding | Controlled studies | |
| Observational studies | High risk, but can be mitigated using matching by propensity scores, etc High risk if there is a failure to adjust for important confounders in the statistical analysis.
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