Levels of evidence for the overall quality of measurement properties from van Tulder et al 56
| Level | Rating | Criteria |
| Strong | +++or --- | Consistent findings in multiple studies of good methodological quality OR in one study of excellent methodological quality |
| Moderate | ++or -- | Consistent findings in multiple studies of fair methodological quality OR in one study of good methodological quality |
| Limited | + or - | One study of fair methodological quality |
| Conflicting | ± | Conflicting findings |
| Unknown | ? | Only studies of poor methodological quality |
+, positive rating; ?, indeterminate rating; -, negative rating.