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Random sequence generation |
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Low risk of bias | The investigators describe a random component in the sequence generation process such as: referring to a random number table; using a computer random number generator. |
High risk of bias | The investigators describe a nonrandom component in the sequence generation process. Usually, the description would involve some systematic, nonrandom approach, for example, sequence generated by odd or even date of birth; sequence generated by some rule based on date (or day) of admission. |
Unclear risk of bias | Insufficient information about the sequence generation process to permit judgement of “Low risk” or “High risk.” |
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Allocation concealment |
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Low risk of bias | Participants and investigators enrolling participants could not foresee assignment because one of the following, or an equivalent method, was used to conceal allocation: central allocation (including telephone, web-based and pharmacy-controlled randomization); sequentially numbered drug containers of identical appearance. |
High risk of bias | Participants or investigators enrolling participants could possibly foresee assignments and thus introduce selection bias, such as allocation based on using an open random allocation schedule (e.g., a list of random numbers); assignment envelopes were used without appropriate safeguards (e.g., if envelopes were unsealed or nonopaque or not sequentially numbered). |
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Blinding of participants and personnel |
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Low risk of bias | Any one of the following: no blinding or incomplete blinding, but the review authors judge that the outcome is not likely to be influenced by lack of blinding; blinding of participants and key study personnel ensured, and unlikely that the blinding could have been broken. |
High risk of bias | No blinding or incomplete blinding, and the outcome is likely to be influenced by lack of blinding; blinding of key study participants and personnel attempted, but likely that the blinding could have been broken, and the outcome is likely to be influenced by lack of blinding. |
Unclear risk of bias | Any one of the following: insufficient information to permit judgement of “Low risk” or “High risk”; the study did not address this outcome. |
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Blinding of outcome assessment |
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Low risk of bias | Any one of the following: no blinding of outcome assessment, but the review authors judge that the outcome measurement is not likely to be influenced by lack of blinding; blinding of outcome assessment ensured, and unlikely that the blinding could have been broken. |
High risk of bias | Any one of the following: no blinding of outcome assessment, and the outcome measurement is likely to be influenced by lack of blinding; blinding of outcome assessment, but likely that the blinding could have been broken, and the outcome measurement is likely to be influenced by lack of blinding. |
Unclear risk of bias | Any one of the following: insufficient information to permit judgement of “Low risk” or “High risk”; the study did not address this outcome. |
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Incomplete outcome data |
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Low risk of bias | Any one of the following: no missing outcome data; reasons for missing outcome data unlikely to be related to true outcome (for survival data, censoring unlikely to be introducing bias). |
High risk of bias | Any one of the following: reason for missing outcome data likely to be related to true outcome, with either imbalance in numbers or reasons for missing data across intervention groups; for dichotomous outcome data, the proportion of missing outcomes compared with observed event risk enough to induce clinically relevant bias in intervention effect estimate. |
Unclear risk of bias | Any one of the following: insufficient reporting of attrition/exclusions to permit judgement of “Low risk” or “High risk” (e.g., number randomized not stated, no reasons for missing data provided); the study did not address this outcome. |
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Selective reporting |
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Low risk of bias | Any of the following: the study protocol is available and all of the study’s pre-specified (primary and secondary) outcomes that are of interest in the review have been reported in the prespecified way; the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre-specified (convincing text of this nature may be uncommon). |
High risk of bias | Any one of the following: not all of the study’s prespecified primary outcomes have been reported; one or more primary outcomes is reported using measurements, analysis methods, or subsets of the data (e.g., subscales) that were not prespecified. |
Unclear risk of bias | Insufficient information to permit judgement of “Low risk” or “High risk.” It is likely that the majority of studies will fall into this category. |
Other bias |
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Low risk of bias | The study appears to be free of other sources of bias. |
High risk of bias | There is at least one important risk of bias. For example, the study had a potential source of bias related to the specific study design used, or has been claimed to have been fraudulent; or had some other problem. |
Unclear risk of bias | There may be a risk of bias, but there is either insufficient information to assess whether an important risk of bias exists or insufficient rationale or evidence that an identified problem will introduce bias. |
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