Table 1 Quality assessment tool

Patients/selection bias

1) Is the hypothesis/aim/objective of the study clearly described?

2) Are the characteristics of the patients included in the study clearly described?

3) Is the patient sample representative of patients treated in routine clinical practice?

4) Is there information on possibility of selection bias present in study?

Interventions

5) Are the interventions of interest clearly described? Treatments should be clearly described. In non-treatment related observational studies the characteristics under study should be clearly described.

Comparison

6) Was a comparison group identified and clearly defined?

Outcomes

7) Are the main outcomes to be measured clearly described in the Introduction or Methods section? If the main outcomes are first mentioned in the Results section, the question should be answered no.

8) Were the main outcome measures used accurate (valid and reliable)? For studies where the outcome measures are clearly described, the question should be answered yes. For studies which refer to other work or that demonstrates the outcome measures are accurate, the question should be answered as yes.

9) Have all important adverse events that may be a consequence of the intervention been reported? This should be answered yes if the study demonstrates that there was a comprehensive attempt to measure adverse events. (A list of possible adverse events is provided).

Reported findings/statistical analysis

10) Are the main findings of the study clearly described? Simple outcome data (including denominators and numerators) should be reported for all major findings so that the reader can check the major analyses and conclusions.(This question does not cover statistical tests which are considered below)

11) Does the study provide estimates of the random variability in the data for the main outcomes? In non normally distributed data the inter-quartile range of results should be reported. In normally distributed data the standard error, standard deviation or confidence intervals should be reported. If the distribution of the data is not described, it must be assumed that the estimates used were appropriate and the question should be answered yes.

12) Were the statistical tests used to assess the main outcomes appropriate? The statistical techniques used must be appropriate to the data. For example nonparametric methods should be used for small sample sizes. Where little statistical analysis has been undertaken but where there is no evidence of bias, the question should be answered yes. If the distribution of the data (normal or not) is not described it must be assumed that the estimates used were appropriate and the question should be answered yes.

Confounding

13) Are the distributions of principal confounders in each group of subjects to be compared clearly described? A list of principal confounders is provided.

14) Was there adequate adjustment for confounding in the analyses from which the main findings were drawn?

Losses to follow-up

15) Were losses of patients to follow-up reported?

16) Were losses of patients to follow-up taken into account? If the numbers of patients lost to follow-up are not reported, the question should be answered as unable to determine. If the proportion lost to follow-up was too small to affect the main findings, the question should be answered yes.

Power

17) Was a sample size calculation reported?

18) Did the study have sufficient power to detect a clinically important effect where the probability value for a difference being due to chance is less than 5%?Sample sizes have been calculated to detect a difference of x% and y%.