Limitations and strengths
As in any study, in the data presented in the WORKss Cohort Platform, there are limitations that should be taken into account.
- The data presented is descriptive, without a statistical analysis to assess the possible interactions between the age effect, which, as expected, is clearly observed, and the period and the cohort effects. However, based on other studies, we can rule out the period effect, keeping the annual incidence of IP and MP stable. In future studies, the cohort effect, which seems to occur, would have to be thoroughly analyzed.
- Since there may be changes in occupation and/or economic activity throughout the follow-up period, we have assumed that each individual is annually assigned to the category in which they have been the longest for that year, which, in some cases, may affect the calculation of the rate in a certain category.
- Permanent disability and premature mortality are presented without medical diagnosis. If available, this would help improve the monitoring of formulating more specific conclusions on the trends in the incidence of IP and MP.
- Likewise, and although we do not know precisely the completeness of the registry of deaths in the CWLS, we have observed that the age-specific rates (25-34, 35-44 and 45-54) are always lower than those recorded by the National Institute of Statistics 9 for the whole population in 2004 and 2015, which indicates, quite possibly, a healthy worker effect 10. That is, people who work are, in principle, the healthiest, so their disability and mortality are lower.
- Finally, it must be taken into account that workers who do not have coverage (informal employment), which are estimated to be around 5% 11, are not included, nor are self-employed workers, around 15% 12. The latter have been excluded because a permanent disability analysis could not be done since, during the study period, they have no coverage for permanent disability, but the incidence of premature mortality could have been assessed. This is a limitation that could be addressed in future updates.
However, there are also a number of strengths that give us confidence about the usefulness of the results shown in the WORKSss Cohort Platform:
- The database allows us to observe the longitudinal trend of the incidence of two phenomena of such sanitary relevance as IP and MP in relation to the working life of people included in the CWLS. In addition, the data are of quality and collected and prepared for management purposes.
- Having the onset and end date of sick leave, death, working situation has allowed to calculate, precisely, the exact time that a worker has been at risk of receiving a permanent disability or has been at risk of dying, and thus, we have been able to calculate the exact incidence density.
- The first twelve years of follow-up available may continue to expand as the new annual data of the CWLS are published.