Results from this study show that the risk of occupational injury is unequally distributed between temporary and permanent employment: temporary workers have higher risk than permanent workers. However, after adjusting by occupation, and particularly length of employment, the risk of occupational injury among temporary workers approximates that of permanent workers. These findings provide some evidence about the link between type of employment and the risk of occupational injury.
Our results confirm earlier studies that found an excess risk of occupational injury among temporary workers,12
and provides new insight into the mechanism underlying the association. These findings need to be replicated before they are taken as causal evidence. The study of this association in other countries, especially those with a lower proportion of temporary workers, would seem to be a logical next step since there is no guarantee that temporary employment has the same meaning and health effect impact in different countries.
Despite occupational injury statistics being considered complete in Spain,16,18
the accuracy of specific items such as type of employment or length of employment is unknown, and it is possible that temporary workers might be more likely to have inaccurate data than permanent workers. Furthermore, temporary workers may be underreporting occupational injuries because of fears of being stigmatised or fired,23
which would lead to an underestimate of the strength of the association. Primary data collection is needed to improve the measurement of temporary employment and confirm our findings. Indeed, given that temporary workers are likely to have fewer work hours actually worked, the true risk may actually be understated by the population denominator used in this study.
Conversely, the cross sectional design of the study could lead to an overestimation of the strength of reported association, because an inverse relation could be possible: workers with a high frequency of occupational injuries could lose opportunities to become permanent in their jobs. This hypothesis should be tested in a longitudinal framework study, although it is likely that this selection bias influence would be small.
According to our hypothesis, the association between temporary employment and occupational injuries can be explained by two mechanisms. Firstly, temporary workers are exposed to more hazardous working conditions than permanent workers. As observed from the distribution of workers by occupation: 26.1% of temporary workers versus 12.2% of permanent workers had non‐qualified and elementary occupations, and 16.3% versus 30%, respectively, had management, professional, or technical occupations. In fact, the Third European Survey on Working Conditions has shown that workers with non‐permanent contracts are more likely to have unfavourable working conditions such as repetitive movements, painful and tiring positions, discrimination, low time control, and/or less freedom to choose when to take personal leave.24
Spanish surveys on working conditions show a similar pattern, especially in relation to ergonomic and psychosocial risk factors.25
In conclusion, on the whole, temporary workers toil in occupations with more hazardous working conditions. However, within occupational groups, temporary workers show significantly higher risks than permanent workers in almost all occupations, especially for non‐fatal injuries. An explanation for this remarkable finding could be that temporary workers have less experience and knowledge of the workplace than permanent workers. In fact, when the length of employment is taken into account the observed association disappears in each group (data not shown), except for skilled agricultural and fishery workers. An alternative explanation could be that there were only nine occupational categories, and within each category there are different types of jobs. This may have led to underadjustment of the role of occupationally linked working conditions in the study. However, the persistent effect of temporary work in relatively homogeneous strata of occupations suggests that the first explanation has substantial merit. The role of working conditions in the observed association should be further assessed with more detailed information on work organisation and workplace hazards.
An unexpected inverse association was observed between permanent services workers, and skilled agricultural and fishery workers and fatal occupational injuries. A plausible explanation could be that many temporary workers in these occupations are self‐employed, and do not record suffering occupational injuries.21
A second mechanism should be considered as a possible explanation for these findings: permanent workers are likely to have better knowledge and experience of the workplace, tools, and activities than temporary workers. The results show, on the one hand, a clear inverse trend between length of employment and occupational injury risk, among both permanent and temporary workers: risk decreases when length of employment increases. However on the other hand, the RR was only statistically significant for permanent workers. These patterns did not change significantly after taking into account occupation. Both results are not paradoxical. Less than six months is the most hazardous employment situation in any case, and experience within the workplace protects against occupational injury risk, but this protection is less in the case of a worker with a temporal contract of less than 24 months of duration.
Conversely, despite older workers having more experience and compensating ability (safer work behaviours),26
aging seemed to increase the risk of occupational injuries, especially fatal occupational injuries, among temporary workers. This could be partly due to the cumulative effect of hazardous exposures among temporary workers, to a lesser capacity of adaptation to changes in working conditions, and also to their age related weakness and vulnerability when facing occupational exposures.
This significant role played by the length of employment has to be considered with caution, because given the cross sectional design of the study and the time related nature of the length of employment, it is likely that some potential bias could affect the results. For instance, workers with less than six months of employment, where the risk of occupational injury was highest, have less probability of being included in a cross sectional study than workers with more than 24 months. However, this bias, if present, could underestimate the magnitude of the association.
Finally, a significant association persisted for fatal injuries clearly related to work after adjusting by occupation and length of employment. Other mechanisms could explain this excess risk among temporary workers. A new hypothesis is that temporary workers are exposed to more stressful circumstances due to greater job vulnerability than permanent workers. Recently, it has been observed that the relation between psychosocial risk factors and sickness absence was stronger among non‐permanent workers than permanent workers.27
This association has been explained in terms of an increase in effort and productivity. It could, therefore, be suggested that temporary workers have a greater risk of occupational injury because they work at a more accelerated pace. The need to save time and tighter schedules, which significantly affect subcontractors, have been identified as risk factors in a series of 99 serious occupational injuries.28
- Findings confirm that temporary workers have a significantly higher risk of having fatal and non‐fatal occupational injuries than permanent workers.
- Lower job experience of temporary workers may partially explain why they are at a higher risk of experiencing occupational injuries.
- The role of working conditions should be specifically investigated regarding the association between temporary employment and occupational injuries.
- Promoting a higher level of permanent employment, with all of its benefits, is an important way towards preventing occupational injuries.
- Increasing workers' knowledge of workplace hazards, especially among temporary workers, is an additional way of reducing the risk of occupational injuries.
The association found in this study, attributed to the multiple vulnerabilities associated with temporary employment, should be assessed more specifically and in greater detail. Other mechanisms related to precarious employment such as the structural characteristics of the workplace (lack of unionisation or social benefits), or discrimination by both supervisors and permanent workers, should also be taken into account in further analyses.12
In conclusion, promoting a higher level of permanent employment, with all of its attendant benefits, is clearly one way to prevent the risk of occupational injury, especially in Spain where the level of temporary employment is extremely high. However, increasing workers' knowledge of their workplace, especially among temporary workers, could be an additional way to reduce the risk of occupational injury.