Background
Long-term sickness absence is a major social, economic and health problem. It accounts for the majority of the costs of all sickness absence [
1] and reflects ill health [
2]. The most common diagnostic causes of long-term sickness absence are musculoskeletal diseases and mental disorders [
1,
3‐
5]. Sickness absence due to mental disorders increased from the 1990s until the early 2000s [
3‐
5], but a downward trend has been reported since the mid-2000s [
5,
6]. There has been an equivalent trend in sickness absence due to musculoskeletal diseases in Finland [
5], whereas sickness absence due to injuries, for instance, has remained relatively stable over time [
5]. Previous studies have shown that those in lower occupational classes have more sickness absence (see, for instance) [
7‐
10], and that class differences have persisted over time [
11‐
14]. However, little is known about changes over time regarding occupational class differences in sickness absence attributable to different diagnostic causes.
Previous studies examining diagnostic-specific sickness absence have shown hierarchical occupational class differences in work-injury-related absences [
15‐
18] and absence attributable to different somatic causes such as musculoskeletal diseases [
16,
19‐
21], respiratory diseases [
16,
22] and digestive disorders [
15]. With regard to cardiovascular diseases, some studies report class differences only among men [
15,
23]. Previous findings on mental disorders are mixed [
15,
16,
24], and the results differing between specific diagnoses [
25]. However, only few studies have examined occupational class differences in sickness absence simultaneously across several diagnostic causes. A British study [
15] reported particularly large differences in long (7+ days) periods of sickness absence related to musculoskeletal diseases, injuries and respiratory diseases, and diagnosed mental disorders, such as depression and anxiety. A French study [
16], in turn, revealed large occupational class differences in sickness absence related to musculoskeletal diseases and, among men, injuries, but the class differences were less profound in the case of mental disorders among both women and men.
Various factors have been shown to influence occupational class differences in sickness absence. Occupational class is a key indicator of socioeconomic position and implies, for instance, differences in physical and psychosocial working conditions across the occupational class hierarchy [
26]. Previously, different work-related factors, in particular deleterious physical working conditions, have been shown to explain a major part of the observed hierarchical occupational class differences in sickness absence [
7,
9,
10]. A French study [
16], examining the contribution of work-related factors with occupational class differences in diagnostic-specific sickness, found that both adverse physical and psychosocial work-related factors were associated with the class differences in sickness absence due to musculoskeletal diseases. The class differences in sickness absence attributable to mental disorders were mainly related to work-stress factors, in particular low decision latitude and low social support, and adverse physical working conditions explained the occupational class gradient in sickness absence due to injuries [
16]. Other main explanations for the occupational class differences in sickness absence have been shown to relate to health behaviours, such as smoking, alcohol consumption, weight and physical activity [
7,
9] and to a minor extent ill health [
10]. Poor health may also lead to poorer education and, thus, hinder occupational attainment [
26]. Health-related selection may hence play a role in formation of the occupational class differences in sickness absence [
16]. High education provides also knowledge and skills, thus enabling to make better choices in order to promote health [
26]. Similarly poor health may lead to poor income and, thus, hinder access to health services and health promotive resources, such as good quality food and leisure time activities [
26].
Although several studies have examined occupational class differences in diagnostic-specific sickness absence and explanatory factors to the class disparities, few have focused on changes in occupational class differences in diagnostic-specific sickness absence over time. Currently, several member countries of the Organisation for Economic Co-operation and Development (OECD) consider extension of working lives, for instance by reducing sickness absence, a key target due to ageing workforce [
27]. In Finland, various legislative amendments were executed in the early 2010s in order to prevent work disability and employees’ permanent exit from labour market [
28]. Diagnostic-specific information on occupational class differences in sickness absence could improve the identification of high-risk groups in terms of work disability, the detection of potential changes in these groups and the targeting of preventive measures effectively in the future [
29]. Moreover, the assessment of health and work-life policy interventions calls for monitoring longitudinal trends in socioeconomic differences in health [
30]. Reducing socioeconomic inequalities in health has been a key goal in many Finnish health policy programs over the years [
31]. During the past decades, socioeconomic health inequalities have remained large in Finland as well as in many European countries [
32]. However, little is known about trends over time in diagnostic-specific sickness absence.
Our aim was to examine the magnitude of and changes over time in occupational class differences in long-term sickness absence due to major diagnostic causes, focusing on Finnish women and men during the period 2005–2014. We assessed class differences by means of both absolute and relative measures. This method has been used infrequently in previous studies [
33], despite the recommendation of the World Health Organization’s Commission on Social Determinants of Health to use both scales for monitoring socioeconomic inequalities in health over time, thereby giving a more precise picture of the absolute and relative differences [
34].
Discussion
This study examined the magnitude of and changes over time in absolute and relative occupational class differences in long-term sickness absence due to major diagnostic causes among Finnish women and men. The large nation-wide data set comprised approximately 1.2–1.3 million persons annually between 2005 and 2014. The three most common diagnostic causes of absence were musculoskeletal diseases, mental disorders and injuries. The prevalence in the other diagnostic categories was low, at most approximately 1 %.
The main findings could be summarised thus. 1) Occupational class differences were by far the largest in the case of long-term sickness absence due to musculoskeletal diseases among both women and men. The relative class differences were particularly large among men throughout the study period. The absolute differences in both genders and the relative differences among men narrowed over time, the prevalence of absences thus attributable declining most rapidly among manual workers. 2) Occupational class differences in sickness absence due to mental disorders were small. Absolute differences were non-existent among men and modest among women, and there were no significant changes over time in relative differences. 3) With regard to injuries, there were stable absolute class differences: among men the relative differences tended to narrow over time in that the prevalence of sickness absence declined most among manual workers. 4) As far as the other diagnostic causes under scrutiny were concerned, there were rather large relative occupational class differences in some cases, such as in diseases of the nervous system, but in absolute terms the class differences appeared negligible throughout the study period.
Our results were consistent with those reported in previous studies showing large occupational class differences in sickness absence due to musculoskeletal diseases [
16,
19‐
21]. A large part of the socioeconomic gradient could well be attributable to differences in health, health behaviours and working conditions, which tend to be more detrimental in manual occupations. Heavy physical work demands, uncomfortable working positions, job dissatisfaction and work stress, for example, have been shown to increase the risk of sickness absence due to musculoskeletal diseases [
42,
43]: it was found in a French study [
16] that physical and psychosocial work-related factors explained almost half of sickness absence on such grounds among men, and nearly one third among women. Part of the class differences in sickness absence due to musculoskeletal diseases could be attributed to health behaviours [
7,
9]; excess weight and smoking, for instance, constitute important risk factors for several musculoskeletal diseases [
44]. Overall, higher musculoskeletal morbidity in lower occupational classes [
45] also play a role in the formation of the class differences in sickness absence due to musculoskeletal diseases in a working population.
According to our results, both absolute and relative occupational class differences in sickness absence due to musculoskeletal diseases narrowed over time among men, and there was also a declining trend in absolute differences among women. The prevalence decreased in all occupational classes, but in particular among manual workers. The alleviation of physical work demands, for instance as a consequence of increased mechanisation of work, in recent years could explain part of the change [
46]. Finnish employees have also reported improvements in occupational safety and health [
46]. On the other hand, job insecurity caused by the economic downturn since 2008 may have led to a decline in sickness absence [
13,
47], in particular among employees in lower occupational positions [
48]. Despite the narrowing trend, however, class differences in sickness absence due to musculoskeletal diseases remained large throughout the study period.
We found that occupational class differences in long-term sickness absence due to mental disorders were at most modest, and remained stable over time. Previous findings on socioeconomic differences in such sickness absence have been mixed, with evidence of a reverse association [
15,
24], an inconsistent association [
16] and no association for some specific mental diagnoses [
25]. In the present study, the proportion of individuals granted sickness absence in these grounds was highest among lower non-manual workers. This occupational class comprises many physically but also mentally demanding occupations (such as nursing, practical nursing, and child-minding). Mentally strenuous working conditions, such as low decision latitude and low social support, have been shown to account for almost 50% of sickness absence related to mental disorders [
16]. Less consistent socioeconomic gradients in minor psychiatric disorders [
49] may also be reflected in our results. The prevalence of absence on the grounds of mental disorders was fairly low in all the occupational classes under study, however, which could be partially attributable to the health-related selection of employees. Previous studies have shown that poor mental health increases the risk of subsequent unemployment [
50] and permanent work disability [
51].
Our study revealed clear occupational class differences in sickness absences due to home and leisure injuries, which are the most common types of injury among Finnish working-age people [
52]. This finding is in line with the results of previous studies showing hierarchical socioeconomic differences in sickness absence due to work injuries [
15‐
18]. Overall, there are clear socioeconomic differences in the risk of injury in both work-related and non-occupational settings [
53], and the main explanations lie in individual and contextual factors [
54]. The major contributors to injuries among Finnish working-age population include medication, drugs and alcohol [
52]. Unhealthy alcohol drinking habits have been previously shown to increase the risk of medically certified sickness absence [
55]. The risk of alcohol-related health consequences tends to be higher among manual workers than among those in higher classes, even with the same consumption levels [
56]. These findings may, at least in part, explain our results which could also have been affected by the diverse work-ability requirements in different occupations. In addition, employees in higher occupational classes may have better opportunities to adapt work tasks compared to employees in lower classes. Relative differences tended to narrow among men between 2005 and 2014, however, as the prevalence decreased among manual workers over the study period. One explanation for this change could be the price increase in alcohol following the tightening of taxation, and the consequently reduced alcohol consumption in Finland since 2007 [
57]; previous studies have indicated that changes in alcohol prices have biggest effect on alcohol consumption [
58] and alcohol-related harm [
59] among manual workers, and men in particular.
The prevalence of the other studied diagnostic causes of sickness absence under study was low, and the absolute class differences modest. The relative differences in diseases of nervous system were somewhat large, although they narrowed among women during the study period, the prevalence declining most among manual workers. Socioeconomic differences in morbidity could help to explain class differences in long-term sickness absence attributable to diseases of nervous system [
60]: for instance, some manual occupations such as construction workers, dry cleaners and launderers carry an increased risk of hospitalization due to epilepsy, one cause of which is suggested to be frequent exposure to chemicals [
61].
The magnitude of occupational class differences in sickness absence varied in the present study depending on the diagnostic cause. This is consistent with the finding of previous studies examining socioeconomic differences in sickness absence simultaneously across various disease categories [
15,
16]. A medical diagnosis is a prerequisite for prolonged absence from work, and a certified sickness absence is granted only if a disease leads to an imbalance between work ability and demands [
3]. Our results, in line with those reported in earlier studies, imply that the contribution of factors related socioeconomic position, such as ill health, deleterious health behaviours, and physical and psychosocial working conditions, to sickness absence may also differ depending on a disease for sickness absence. Further, our study showed that changes over time in the class differences varied between different diagnostic causes. The class differences have remained relatively stable in several different diagnostic categories over time. Similar trend has been detected previously in both absolute and relative occupational class differences in health in Finland [
32]. However, a narrowing trend in the class differences was found in sickness absence attributable to musculoskeletal diseases in the present study. This change is noteworthy since musculoskeletal diseases constitute the single most common diagnostic cause of long-term sickness absence in Finnish working population. The potential for prevention has previously been shown to be particularly high in the case of musculoskeletal diseases [
62]. In the future, preventive actions should be continued and targeted particularly to lower occupational classes and to the major diagnostic causes for long-term sickness absence, i.e. musculoskeletal diseases, mental disorders and injuries, when attempting to reduce sickness absence and narrow the class differences.
Strengths and limitations
This study was based on a nationally representative sample of the Finnish working-age population covering a 10-year period and obtained from a comprehensive national register database. The sample data was linked to register data on sickness absence episodes exceeding 10 working days, with practically no missing information. All such episodes were medically certified, thus eliminating self-report bias. Additionally, the data covered a broad range of diagnoses. Data on occupational class (upper non-manuals, lower non-manuals and manual workers) were retrieved from a national register comprising information from several occupations in different sectors. We used both absolute and relative measures to examine occupational class differences in sickness absence, which is rare done in previous studies. Our results can be directly generalised to the labour force in Finland and with caution to other countries as well with regard to the occupational classes under scrutiny.
The present study also has some limitations. For instance, we were unable to suggest explanations for the class differences in sickness absence attributable to the different diagnostic causes because we lacked national register data on morbidity, health-related behaviours and working conditions. Nation-wide register data cover all sickness absence episodes in Finland lasting longer than 10 working days based on sickness allowance paid by Kela. However, there are no national registers incorporating shorter sickness absence episodes, which could therefore not be included in this study. Short sickness absence is more typical, in cases of respiratory diseases and gastrointestinal infections, for instance, whereas absences tend to be longer in cases of musculoskeletal diseases and mental disorders [
15]. A British study [
15] examined socioeconomic differences in shorter (7 days or less) periods of sickness absence due to several diagnostic causes, and also reposted particularly large differences in gastrointestinal infections and other diseases of the digestive system. This could have been the case in our study had we included shorter sickness absence episodes in the analyses.