Quality assessment criteria
| 1 | Did the sample represent the population of interest? |
| 2 | Was loss to follow-up <35% and response rate >65%? |
| 3 | Were the prognostic factors measured with valid and reliable instruments? |
| 4 | Was the outcome of the study objectively measured? |
| 5 | Were important potential confounders (ie, age, gender, prior WA and comorbidity) appropriately accounted for in the analysis? |
| 6 | Was the statistical analysis appropriate? |
WA, work absence.