Table 1

Quality assessment criteria of trials
Selection bias
Score Criteria Impact on bias risk
Randomisation and concealment
A Randomisation: Details of any adequate type of allocation method that generates random sequences, with the patient as unit of randomization, are reported.1 Doubts may still exist about whether the trial results are influenced by selection bias but no indication can be found in the trial report to support such doubt.
Concealment: Trial provides evidence2 that concealment was indeed effective and that the random sequence could not have been observed or predicted throughout the duration of the trial.
B Randomisation: Details of any adequate type of allocation method that generates random sequences, with the patient as unit of randomisation,are reported.1 Despite the implementation of a method considered able to prevent unmasking of the concealed allocation sequence through direct observation and prediction, there are reasons to expect that the concealed allocation sequence may have been unmasked during the course of the trial.
Concealment: Trial reports on any adequate method for preventing direct observation3 and prediction4 of the allocation sequence and sequence generation rules.
C Randomisation: Details of any adequate type of allocation method that generates random sequences, with the patient as unit of randomization, are reported.1 Despite the implementation of a method considered able to prevent unmasking of the concealed allocation sequence through direct observation, there are reasons for expecting that operators could have predicted the concealed allocation sequence.
Concealment: Trial reports on any adequate method to prevent direct operator observation of allocation sequence and sequence generation rules3. However, the allocation sequence and sequence generation may have been sufficiently predicted.
D Randomisation: Details of any adequate type of allocation method that generates random sequences, with the patient as unit of randomization, are reported.1 Despite the theoretical chance for each patient to be allocated to either treatment group, operator knowledge of the allocation sequence may have led to patient allocation that favoured the outcome of one type of treatment above the other.
Concealment: The trial report does not include information on how the allocation of random sequence was concealed. The allocation could have been directly observed and/or predicted.
0 Trial does not comply with criteria A – D. No guarantee of equal chance for patients to be allocated to either treatment group. Thus allocation may have favoured the outcome of one type of treatment above the other.
Baseline data for randomised trials
A Baseline data collected before randomisation and reported for both treatment groups. Data shows no significant differences between both groups. Evidence is given that randomisation has led to equal groups, suggesting little risk of selection bias.
B Baseline data collected before randomisation and reported for both treatment groups. Data shows significant differences between both groups but has been appropriately statistically adjusted. Differences have been adjusted. Thus the influence of possible selection bias appears to be reduced.
C Baseline data collected before randomisation and reported for both treatment groups. Data shows significant differences between both groups without being statistically adjusted. Reported differences may be due to ineffective randomisation, thus indicating risk of selection bias.
0 Trial does not comply with criteria A – C. No evidence is given as to whether randomisation has indeed led to equal groups with differences beyond chance. Thus differences may exist, indicating selection bias.
Detection/Performance bias
Blinding/Masking
Score Criteria Impact on bias risk
A Trial reports on any type of method that is known to prevent patient AND operator AND evaluator from discerning whether patients are allocated to the test- or the control group (Blinding/Masking). Evidence is given that the trial results may not have been influenced by detection/performance bias which may have favored the outcome of one type of treatment above the other.
Trial reports a process by which the effect of Blinding/Masking was evaluated, as well as the results of such evaluation.
B Trial reports on any type of method that is known to prevent patient AND operator AND evaluator from discerning whether patients are allocated to the test- or the control group (Blinding/Masking). Doubts may still exist about whether the trial results are influenced by detection/performance bias but no indication can be found from the trial report to support such doubt. However, no evaluation of the blinding/masking effect has been included in the trial. Thus no evidence for lack of bias is given.
Trial report does not give reason for doubt that the patient allocation to either the test- or the control group has been unmasked throughout the duration of the trial.
C Trial reports on any type of method that is known to prevent patient AND operator AND evaluator from discerning whether patients are allocated to the test- or the control group (Blinding/Masking). Despite the implementation of a method considered able to prevent unmasking, there are reasons to expect that operators/patients could have discovered the allocation.
Trial report gives reason for doubt that the patient allocation to either the test- or the control group has been unmasked throughout the duration of the trial.
0 No process able to blind/mask patients AND operators as to whether patients were allocated to either the test- or the control group reported or implemented (It is insufficient to report that blinding/masking was done without reporting the details of the process). Knowledge about the patient allocation may have caused patients/operator to act in a way that may have favoured the outcome of one type of treatment above the other,
Attrition bias
Loss – to follow up
Score Criteria Impact on bias risk
A Available case analysis, loss-to-follow-up reported per treatment group. Subsequent sensitivity analysis does not indicate a possible risk of bias. The trial allows extraction of evidence that attrition may not have favoured the outcome of one type of treatment above the other.
B Available case analysis, loss-to-follow-up reported per treatment group. Subsequent sensitivity analysis indicates a possible risk of bias. The trial allows assessment of the risk that attrition may have favoured the outcome of one type of treatment above the other.
0 Trial does not report number of included participants per treatment group at baseline or gives any indication that would allow ascertaining of the loss-to-follow up rate per treatment group. The trial carries an unknown risk that attrition may have favoured the outcome of one type of treatment above the other.

1 Excluded are types of allocation methods that are considered as inadequate: cluster randomisation, fixed block randomisation with block size 2, minimisation, alternation, randomisation of teeth, use of date of birth or patient record number, “quasi”-randomisation, split-mouth.

2 E.g. by reporting results of the Berger-Exner Test or any other statistical tests that show that covariates of compared groups were similar at baseline.

3 E.g. by opening of opaque envelope, obtaining allocation from tables, computer generated or from other sources.

4 E.g. central randomisation, sequence allocation by other than operator; excluding varied block randomisation.

Mickenautsch

Mickenautsch BMC Oral Health 2012 12:18   doi:10.1186/1472-6831-12-18

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