| Type of Reporting Bias | Definition |
| Publication bias | The publication or non-publication of research findings, depending on the nature and direction of results. |
| Time-lag bias | The rapid or delayed publication of research findings, depending on the nature and direction of the results. |
| Language bias | The publication of research findings in a particular language, depending on the nature and direction of the results. |
| Citation bias | The citation or non-citation of research findings, depending o the nature and direction of the results. |
| Multiple (duplicate) publication bias | The multiple or singular publication of research findings, depending on the nature and direction of the results. |
| Location bias | The publication of research findings in journals with different ease of access or levels of indexing in standard databases, depending on the nature and direction of results. |
| Selective (non-) reporting bias | The selective reporting of some outcomes or analyses, but not others, depending on the nature and direction of the results. |
| Funding bias | Funders may have a vested interest in demonstrating positive outcomes for one group/intervention. |
| Confounders | Were the participant characteristics, such as age, sex, or health status, similar across all treatments? Participants should be equally balanced in terms of variables considered important to study outcomes (e.g. sex, age, health status) otherwise there is a risk that results will be biased in favor of one group or intervention. |
| Analysis | Were all the data for all participants included in the final analysis (even those participants who withdrew?) If there are data missing for a number of participants and these are not accounted for, published results will not properly reflect the results of the study. |
Source: Boland, A., Cherry, M. G., & Dickson, R. (2017). Quality Assessment: Where Do I Begin? In Doing a systematic review: A student's guide. essay, Sage.
Wiley-Blackwell. (2019). Cochrane Handbook for Systematic Reviews of Interventions.