Table 5.

Methodological quality of included quantitative studies (n = 8)

Quality category	Studies meeting criterion, n (%)
1. Subject Selection
2. Representative of population of interest	1 (12.5)
1. Selected group	1 (12.5)
0. Highly selected or not described	6 (75.0)
2. Comparability of groups analysed on demographic characteristics
2. Comparable (or matched)	1 (12.5)
1. Not comparable but adjusted analysis used	1 (12.5)
0. Not comparable and not adjusted for differences	3 (37.5)
Not applicable: no comparisons made	3 (37.5)
3. Participation rate
2. High participation rate (>80%) and no important differences between participants and non-participants	0
1. Moderate participation rate (65-80%) and no important difference between participants and non-participants	0
0. Low participation rate (<65%), important differences between participants and non- participants or not described	8 (100)