Job tenure and work injuries: a multivariate analysis of the relation with previous experience and differences by age

Background: One of the consequences of the increasing flexibility in contemporary labour markets is that individuals change jobs more frequently than in the past. Indeed, in many cases, through collecting a lot of contracts, individuals work in the same economic sector or even in the same company, doing the same job in the same way as existing colleagues. A very long literature has established that newly hired workers -- whatever the contract type -- are more likely to be injured than those with longer job tenures. The objectives of this paper are: 1) to study the relationship between job tenure and injury risk taking into account past experience as a possible confounder; and 2) to evaluate how the effects of past experience and job tenure are modified by age. Methods: Using a longitudinal national database, we considered only job contracts starting in 1998--2003 held by men working as blue collars or apprentices in the non-agricultural private sector. We calculated injury rates stratified by job tenure and age. Multivariate analyses were adjusted for background variables and previous experience accrued in the same economic sector of the current job. Results: In the study period 58,271 workers who had experienced 10,260 injuries were observed. These people worked on 115,277 contracts in the six years observed (1.98 contracts per worker). Injury rates decrease with job tenure; the trend is the same in each age group; young workers have both the highest injury rate (9.20; CI 95%: 8.95-9.45) and the highest decrease with job tenure. Previous experience is associated with a decreasing injury rate in all age groups and for all job tenures. Multivariate analyses show that, even after checking for previous experience, workers with job tenure of less than 6 months show always higher relative risks compared with job tenure > 2 years: relative risk is 41% higher among under-thirty workers; it is 22% higher among people over forty. Previous experience is protective against injury risk in workers over thirty: after checking for all other variables, relative risk is lower in workers who have accumulated more than 5 years of experience. Conclusions: In a context in which career fragmentation is increasing, workers find themselves more and more in the "high risk" period and only individuals who are able to build their career with similar jobs may mitigate the higher risks thanks to their past experience. If institutions don't adopt appropriate prevention policies, injury risk is likely to increase, especially among young people.