Factorial Validity of the Work Ability Index Among Employees in Germany.

The sample was limited to employees subject to social security contributions aged 31 to 60 years, so it does not show whether the WAI has the same two-part structure for self-employed people, freelancers, civil servants, younger workers or older workers. Only people employed at sampling were included, so participants may have been healthier and less impaired than the wider population. Detailed occupational groups could not be reported because of data protection, so the result may not apply equally to all jobs. The study tested questionnaire structure only. It did not show that the two separate scores predict sick leave, return to work, early retirement or disability better than the total score. The best model did not meet all fit criteria: TLI was 0.94, below the study's acceptable threshold of 0.97. The German WAI version used a shortened list of 14 disease groups instead of the original 51 diseases, so results may not transfer to versions using the original list.

Do not conclude that the Work Ability Index is useless or that the two-factor scores are proven better predictors. The study only tested how the questionnaire indicators group together. It did not test whether the two scores predict sick leave, return to work, early retirement or disability.