Similarly, little research on issues such as job control and work demands is available for ethnic minority workers, although these are central constructs in occupational stress theory. Available research tends to show that these are important constructs for ethnic minority workers as well. For example, African-American licensed practical nurses (LPNs) report significantly less decision authority and more dead-end jobs (and hazard exposures) than do white LPNs and this difference is not a function of educational differences (Marshall and Barnett 1991); the presence of low decision latitude in the face of high demands tends to be the pattern most characteristic of jobs with low socio-economic status, which are more likely to be held by ethnic minority workers (Waitzman and Smith 1994); and middle- and upper-level white men rate their jobs consistently higher than their ethnic minority (and female) peers on six work design factors (Fernandez 1981).
Some areas of research have almost totally ignored ethnic minority populations. For example, hundreds of studies have examined the relationship between Type A behaviour and occupational stress. White males constitute the most frequently studied groups with ethnic minority men and women almost totally excluded. Available research - e.g., a study by Adams et al. (1986), using a sample of college freshmen, and e.g., Gamble and Matteson (1992), investigating black workersindicates the same positive relationship between Type A behaviour and self-reported stress as that found for white samples.
Most studies of work stress and mental illness have been conducted with scales from Karaseks Demand/Control model (Karasek and Theorell 1990) or with measures derived from the Dictionary of Occupational Titles (DOT) (Cain and Treiman 1981). In spite of the methodological and theoretical differences underlying these systems, they measure similar psychosocial dimensions (control, substantive complexity and job demands) (Muntaner et al. 1993). Job demands have been associated with major depressive disorder among male power-plant workers (Bromet 1988). Occupations involving lack of direction, control or planning have been shown to mediate the relation between socioeconomic status and depression (Link et al. 1993). However, in one study the relationship between low control and depression was not found (Guendelman and Silberg 1993). The number of negative work-related effects, lack of intrinsic job rewards and organizational stressors such as role conflict and ambiguity have also been associated with major depression (Phelan et al. 1991). Heavy alcohol drinking and alcohol-related problems have been linked to working overtime and to lack of intrinsic job rewards among men and to job insecurity among women in Japan (Kawakami et al. 1993), and to high demands and low control among males in the United States (Bromet 1988). Also among US males, high psychological or physical demands and low control were predictive of alcohol abuse or dependence (Crum et al. 1995). In another ECA analysis, high physical demands and low skill discretion were predictive of drug dependence (Muntaner et al. 1995). Physical demands and job hazards were predictors of schizophrenia or delusions or hallucinations in three US studies (Muntaner et al. 1991; Link et al. 1986; Muntaner et al. 1993). Physical demands have also been associated with psychiatric disease in the Swedish population (Lundberg 1991). These investigations have the potential for prevention because specific, potentially malleable risk factors are the focus of study.
Comparative studies of occupational categories suffer from the same flaws as social stratification studies. Thus, a problem with occupational categories is that specific risk factors are bound to be missed. In addition, lifestyle factors associated with occupational categories remain a potent explanation for results.
Several ECA studies have been conducted with more specific occupational categories. In addition to specifying occupational environments more closely, they adjust for sociodemographic factors which might have led to spurious results in uncontrolled studies. High 12-month prevalence rates of major depression (above the 3 to 5% found in the general population (Robins and Regier 1990), have been reported for data entry keyers and computer equipment operators (13%) and typists, lawyers, special education teachers and counsellors (10%) (Eaton et al. 1990). After adjustment for sociodemographic factors, lawyers, teachers and counsellors had significantly elevated rates when compared to the employed population (Eaton et al. 1990). In a detailed analysis of 104 occupations, construction labourers, skilled construction trades, heavy truck drivers and material movers showed high rates of alcohol abuse or dependence (Mandell et al. 1992).
Census categories for occupations constitute a readily available source of information that allows one to explore associations between occupations and mental illness (Eaton et al. 1990). Epidemiological Catchment Area (ECA) study analyses of comprehensive occupational categories have yielded findings of a high prevalence of depression for professional, administrative support and household services occupations (Roberts and Lee 1993). In another major epidemiological study, the Alameda county study, high rates of depression were found among workers in blue-collar occupations (Kaplan et al. 1991). High 12-month prevalence rates of alcohol dependence among workers in the Unites States have been found in craft occupations (15.6%) and labourers (15.2%) among men, and in farming, forestry and fishing occupations (7.5%) and unskilled service occupations (7.2%) among women (Harford et al. 1992). ECA rates of alcohol abuse and dependence yielded high prevalence among transportation, craft and labourer occupations (Roberts and Lee 1993). Workers in the service sector, drivers and unskilled workers showed high rates of alcoholism in a study of the Swedish population (Agren and Romelsjo 1992). Twelve-month prevalence of drug abuse or dependence in the ECA study was higher among farming (6%), craft (4.7%), and operator, transportation and labourer (3.3%) occupations (Roberts and Lee 1993). The ECA analysis of combined prevalence for all psychoactive substance abuse or dependence syndromes (Anthony et al. 1992) yielded higher prevalence rates for construction labourers, carpenters, construction trades as a whole, waiters, waitresses and transportation and moving occupations. In another ECA analysis (Muntaner et al. 1991), as compared to managerial occupations, greater risk of schizophrenia was found among private household workers, while artists and construction trades were found at higher risk of schizophrenia (delusions and hallucinations), according to criterion A of the Diagnostic and Statistics Manual of Mental Disorders (DSM-III) (APA 1980).
There are numerous studies in which the focus has been a single occupation. Depression has been the focus of interest in recent studies of secretaries (Garrison and Eaton 1992), professionals and managers (Phelan et al. 1991; Bromet et al. 1990), computer workers (Mino et al. 1993), fire-fighters (Guidotti 1992), teachers (Schonfeld 1992), and maquiladoras (Guendelman and Silberg 1993). Alcoholism and drug abuse and dependence have been recently related to mortality among bus drivers (Michaels and Zoloth 1991) and to managerial and professional occupations (Bromet et al. 1990). Symptoms of anxiety and depression which are indicative of psychiatric disorder have been found among garment workers, nurses, teachers, social workers, offshore oil industry workers and young physicians (Brisson, Vezina and Vinet 1992; Fith-Cozens 1987; Fletcher 1988; McGrath, Reid and Boore 1989; Parkes 1992). The lack of a comparison group makes it difficult to determine the significance of this type of study.
Mental illness is one of the chronic outcomes of work stress that inflicts a major social and economic burden on communities (Jenkins and Coney 1992; Miller and Kelman 1992). Two disciplines, psychiatric epidemiology and mental health sociology (Aneshensel, Rutter and Lachenbruch 1991), have studied the effects of psychosocial and organizational factors of work on mental illness. These studies can be classified according to four different theoretical and methodological approaches: (1) studies of only a single occupation; (2) studies of broad occupational categories as indicators of social stratification; (3) comparative studies of occupational categories; and (4) studies of specific psychosocial and organizational risk factors. We review each of these approaches and discuss their implications for research and prevention.
Sauter and Swanson (1996) suggest that the relationship between biomechanical stressors (e.g., ergonomic factors) and the development of musculoskeletal problems is mediated by perceptual processes which are influenced by workplace psychosocial factors. For example, symptoms might become more evident in dull, routine jobs than in more engrossing tasks which more fully occupy the attention of the worker (Pennebaker and Hall 1982).
Psychosocial factors may influence the physical (ergonomic) demands of the job directly. For example, an increase in time pressure is likely to lead to an increase in work pace (i.e., increased repetition) and increased strain. Alternatively, workers who are given more control over their tasks may be able to adjust their tasks in ways that lead to reduced repetitiveness (Lim and Carayon 1994).
Individuals who are under stress may alter their work behaviour in a way that increases musculoskeletal strain. For example, psychological stress may result in greater application of force than necessary during typing or other manual tasks, leading to increased wear and tear on the musculoskeletal system.