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| Den Elzen, 2008 [20] | |
| Selection | |
| Representativeness of the sample | 1 |
| Selected group of users | 1 |
| Sample size | 1 |
| Diagnose | 0 |
| Comparability | |
| The study controls for the most important factor(age) | 1 |
| The study controls for any additional factor | 1 |
| Exposure | |
| Ascertainment of the method | 1 |
| Statistical test | 1 |
| Total score | 7/8 |
| Quality of study | High |
