work & stress, 2001, vol. 15, no. 4, 297± 313
Scale reliability and validity of the Karasek `Job Demand-Control-Support’ model in the Belstress study EDWIN PELFRENE² *, PETER VLERICK³ , RUDOLF P. MAK² , PATRICK DE SMET§, MARCEL KORNITZER§ and GUY DE BACKER² ² Vakgroep Maatschappelijke Gezondheidkunde, Universiteit Gent, UZGÐ Block A, De Pintelaan 185, B-9000 Gent, Belgium ³ Vakgroep Personeelsbeleid, Arbeids- en Organisatiepsychologie, Universiteit Gent, H. Dunantlaan 2, B-9000 Gent, Belgium §Laboratoire d’ EpideÂmiologie et de Me decine Sociale, Universite Libre de Bruxelles, Route de Lennik 808, B-1070 Belgium Keywords:
Job Demand-Control-Support model; Job strain; Scale reliability; Validity.
In studies of occupational stress, a leading theoretical model is the `Job Demand-Control-Support’ model (Karasek, and Theorell, 1990). This states that the most adverse job-related strain reactions are to be expected in jobs characterized by high job demands, low control and low worksite support. The reliability and validity of the scales was evaluated in a sample of 21,419 employees out of 25 large companies across Belgium. Participants completed items from the Job Content Questionnaire (Karasek, 1985) in either French or Dutch translation. Data were handled by a French-speaking and a Dutch-speaking centre, respectively. Occupational groups were identi® ed according to the International Standard of Classi® cation, ISCO. Basically, the data support the assumptions of the model. The internal consistency was adequate: Cronbach’s a varied between .77 and .83 for Psychological demands (9-item version), Decision latitude, Supervisor social support and Co-worker social support. These four common factors were clearly distinguished in a factor analysis. A con® rmatory factor analysis pointed to the correlation among these factors and illustrated similar loading structures within subgroups according to age, gender and education. Lower occupational grades tended to display lower mean values of psychological demands and decision latitude than those observed in higher grades. Blue collar workers, at least in men, were found to be less exposed to high strain working conditions (high demands± low control) than clerks and service workers. `Feeling stressed’ was found to be more strongly associated with psychological demands than with decision latitude or social support; the reverse held true for `job satisfaction’.
1. Introduction StressÐ in essenceÐ refers to a perception of an imbalance between the demands made and available resources to match them. The idea is that when it persists, it may cause physical and psychological ill-health (Bonn, and Bonn., 2000). The chronic stressors, *Author for correspondence. e-mail:
[email protected]
Work & Stress ISSN 0267-8373 print/ISSN 1464-5335 online 2001 Taylor & Francis Ltd http://www.tandf.co.uk/journals/ DOI: 10.1080/02678370110086399
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however, cannot be identi® ed directly from physical or chemical measurements. Rather, a conceptual framework is needed to identify and elucidate the stressful characteristics that are involved (Marmot et al., 1999). In studies of occupational or work-related stress, a leading theoretical model that is widely used is the `Job Demand-Control’ model ( JDC model). It was developed by Karasek and ® rst proposed in his 1979 paper (Karasek 1979). In this, he combined two lines of research dealing with the relation between psychosocial work characteristics and well-being. These were the Michigan tradition (French, and Kahn, 1962; Kahn, 1981) and related epidemiological studies (Dohrenwend, and Dohrenwend, 1974; Theorell, 1976), which focused on the health eVects of workload and con¯ icting job demands, and the Job Design tradition that stressed the importance of job control and skill level with respect to job satisfaction and mental health (Hackman, and Lawler, 1971; Hackman, and Oldham, 1980). The JDC model predicts that job strain and subsequent physical or psychological illness results from the interaction of job demands and job control. A ® rst hypothesis, also referred to as the `strain hypothesis’, states that the combination of heavy job demands along with low control over one’s own tasks and conduct during the working day precipitates `high strain’. In contrast, the combination of low demands and high control results in `low strain’ or relaxed jobs. A secondÐ and sometimes overlookedÐ hypothesis of the model is that learning, personal development and active participation in social life have the best possibilities in `active jobs’ characterized by high demands and high control, opposed to `passive jobs’ characterized by low demands and low control. Job demands primarily refers to the psychological demands such as the mental workload, organizational constraints on task completion or con¯ icting demands. Job control, on the other hand, is also referred to in Karasek’s model as the decision latitude of the worker. It relates to the freedom permitted to the worker in deciding how to meet the demands or how to perform tasks and is seen as a composite measure that is built up from two related psychosocial working conditions, e.g. skill discretion and decision authority. It is precisely the opportunity to use skills and make decisions that reduces possible adverse eVects of heavy psychological demands (Karasek, 1979). In the 1980s, the model was elaborated in several ways but the most important extension relates to the addition of a third dimension, worksite social support. According to the extended `Job Demand-Control-Support’ model ( JDCS model), the highest risk of poor psychological well-being and ill-health is to be expected in the `iso-strain group’ with jobs characterized by high demands, low control and low social support or, as one could say, in isolation ( Johnson, and Hall, 1988; Karasek, and Theorell, 1990). The model has served as a paradigm that inspired and engendered a lot of empirical research. For that purpose, Karasek published a standardized and oYcial version of the Job Content Questionnaire ( JCQ), a research tool to assess work-related stress that incorporates the scales that belong to the JDCS model (Karasek, 1985; Karasek et al., 1998). Our study, which has been labelled the `Belstress’ study, uses Karasek’s full recommended JCQ to assess work-related stress in a large non-random sample of the working population in Belgium. The objectives of Belstress are to describe variations of job stress among occupational groups and to study the predictive power of the job stress scales for one year of sickness absence and a 3-year incidence of coronary heart disease (in men only). As such, `Belstress’ is part of a broader longitudinal European study, i.e. Job Stress, Absenteeism and Coronary heart disease European co-operation study [JACE] (Houtman et al., 1999). The purpose of the investigation reported in this paper was to evaluate the scale reliability and the validity of the JDCS scales used to assess `(iso-)strain’ in Belstress. With respect to the validity issue, a distinction was made between factorial, discriminant and external validity.
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2. Method 2.1. Participants In the period between 1994 and 1998, the ® eld work of the `Belstress’ study was conducted in 25 large organizations across Belgium. Among these were 13 large industrial plants, six bank and insurance companies, four public administration organizations and two hospitals, all willing to co-operate with the study. In this set, the target population comprised all employees in the organization in the age-span between 35 and 59 years, according to their year of birth at the onset of the study. All members of the target population were invited through a personal letter to comply with the study. A reply form was included in which each invited employee could freely choose whether or not to participate. The invitations and the data-gathering was co-ordinated by the participating research centres, either connected with the French-speaking Universite Libre de Bruxelles or the Dutch-speaking Universiteit Gent, following a strict manual of operations (Coetsier et al., 1996). For practical purposes, invitation letters were distributed internally within the organizations under the supervision of the occupational health service connected with one such organization. A total of 21,419 participants were reached, which is 48.1% of the invited target population. The sample cannot be considered representative of the Belgian workforce, but can be expected to contain a large variation of exposure to job stress, which is what matters in analytical studies (Kristensen, 1995). Participants were asked to ® ll in the questionnaire and to attend a medical examination designed to monitor cardiovascular risk factors. Recollection of data was strictly under closed form. In turn, each of the participants was mailed a detailed medical report with respect to his or her observed risks. About 2 in 3 respondents ® lled in the Dutch version of the questionnaire, 1 in 3 used the French version. Translations into French and Dutch of the JDCS items were back translated into English and submitted to the JCQ Centre, University of Massachusetts, Lowell. Table 1 provides details of the study population. The large majority were men (76%). Most of the respondents also belonged to the younger age group from 35 to 49 years (73%), particularly so for women. Low, medium and high levels of education were well represented, but in women the medium level was signi® cantly better represented than in men. Occupational groups were identi® ed according to the ® rst digit of the International Standard Classi® cation of Occupations, abbreviated ISCO (ILO, 1990). These occupational grades are seen in table 1. It should be noted that in the ISCO System, the lower grades are given to higher-ranked (i.e. more senior) occupations. `Senior oYcials or managers’, `craft workers’ and `plant or machine operators and assemblers’ were more highly represented in men than women; `clerks’ and `elementary occupations’ were relatively more highly represented in women. The large majority were full-time workers; there was a much larger concentration of part-time workers among women as compared to men.
2.2. Instrument Items designed to measure `Psychological Demands’ (nine items), `Decision Latitude’ (nine items) and `Social Support’ (eight items) are those that belong to the full recommended 1985 version of the Job Content Questionnaire ( JCQ) (Karasek, 1985; Karasek et al., 1998). In the JCQ, psychological demand relates to the perception of work load or role ambiguity, which is distinguished from physical demand. Decision Latitude is composed of two subscales, e.g. Skill Discretion (six items) and Decision Authority (three items). The ® rst subscale refers to the level of skill and creativity required on the job, the second
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Age (years) 35± 49 15,291 50± 59 5,550 Educational level Elementary and Junior High 9,029 High school and some College 6,495 College and Graduate school 5,694 Occupational level (ISCO grades 1± 9) 1. Senior oYcials and managers 1,117 2. Professionals 2,241 3. Technicians and associate professionals 3,662 4. Clerks 5,214 5. Service, shop and market sales workers 1,259 7. Craft and related trades workers 2,754 8. Plant and machine operators/assemblers 2,935 9. Elementary occupations 1,613 Number of hours worked /week
