Table 3.

The modified Downs and Black: assessment of the methodological quality

Study	1. Hypothesis/aim/objective clearly described	2. Main outcomes clearly described	3. Characteristics of patients clearly described	5. Confounders clearly described, matched, adjusted	7. Estimates of the random variability for the main outcomes	10. Probability values reported	11. Were the subjects asked to participate representative of the entire population?	12. Were the subjects prepared to participate representative of the entire population?	15. Blindness of assessors	16. Clear data dredging
[30] [34]	1	1	1	0	1	1	1	0	0	1
[29] [33]	1	1	1	2	1	1	1	1	1	1
[28] [32]	1	1	1	0	1	1	1	1	0	1
[12] [14]	1	1	1	0	1	1	1	0	0	1
Study	18. Appropiate statistical tests	20. Accurate outcome measures	21. Cases & controls recruited from the same population	22. Cases & controls recruited from the same period	25. Adequate adjustment for confounding	26. Losses to follow-up considered	27. Sufficient power to detect a clinically important effect	Rate	Percentage (%)	Quality
[30] [34]	1	1	1	0	0	0	0	10	56	M
[29] [33]	1	1	1	0	1	0	0	15	83	H
[28] [32]	1	1	1	1	0	1	1	14	78	H
[12] [14]	1	1	0	1	0	1	1	11	61	M

Abbreviations: M moderate, H high