Table 2 Criteria for methodological quality assessment and number (%) of studies scoring points for each criterion
| Â | Studies fulfilling the criteria n (%) | ||
|---|---|---|---|
Yes | Partial | ||
Criteria | Â | Â | |
 1 | Were the aims/objectives of the study clear? | 27 (100) | 0 (0) |
Methods | |||
 2 | Was the study design appropriate for the stated aims? | 6 (22) | 21 (78) |
 3 | Were the main features of the study population stated (description of sampling frame, distribution by age and sex/gender)? | 14 (52) | 13 (48) |
 4 | Was the response rate at least 80%? | 2 (8) | 0 (0) |
 5 | Were measures undertaken to address and categorize non-responders? | 3 (11) | 0 (0) |
 6 | Were the exposure and outcome variables measured appropriate to the aims of the study? | 17 (63) | 10 (37) |
 7 | Were standardized methods of acceptable quality used to measure IM?a | 12 (44) | 6 (22) |
 8 | Were standardized methods of acceptable quality used to measure correlates?a | 18 (69) | 6 (22) |
 9 | It is clear what was used to determine statistical significance and/or precision estimated (e.g., p values, confidence intervals)? | 23 (85) | 2 (8) |
Results | |||
 10 | Were the results internally consistent? | 26 (96) | 1 (4) |
 11 | Were the results presented for all the analyses described in the methods? | 23 (85) | 4 (15) |