Table 1 Modified Downs & Black Quality Index

Q1. Is the hypothesis/objective of the study clearly described?

Q2. Are the main outcomes to be measured clearly described in the Introduction or Methods?

Q3. Are the characteristics of the patients included in the study clearly described?

Q5. Are the distributions of principal confounder in each group of subjects to be compared clearly described?

Q6. Are the main findings of the study clearly described?

Q7. Does the study provide estimates of the random variability in the data for the main outcomes?

Q10. Have actual probability values been reported (e.g. 0.035 rather than < 0.05) for the main outcomes except where the probability value is less than 0.001?

External Validity

Q11. Were the subjects asked to participate in the study representative of the entire population from which they were recruited?

Internal Validity-Bias

Q15. Was an attempt made to blind those measuring the main outcomes of the intervention? (only for retrospective studies)

Q16. If any of the results of the study were based on “data dredging”, was this made clear?

Q18. Were the statistical tests used to assess the main outcomes appropriate?

Q20. Were the main outcome measures used accurate (valid and reliable)?

Internal Validity-Confounding

Q21. Were the patients in different intervention groups (trials and cohort studies) or were the cases and controls (case–control studies) recruited from the same population? (only for retrospective studies)

Q27. 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%?