Job Strain, Social Class and CVD

Cardiovascular disease

CVD – cross-sectional – stronger effect for Swedish blue-collar men

CVD – cohort – stronger effect for Swedish blue-collar men

CVD mortality – case-control – stronger effect for Swedish men
with less than high-school education

CHD – cohort – stronger effect for Framingham clerical women

MI – case-control – slightly stronger effects among white- collar workers (Sweden)

CVD morbidity – cross-sectional – similar (NS) effects for blue-collar vs white-collar Swedish women

CVD mortality – cohort – stronger effects for low work control
and low social support for white-collar vs blue-collar Swedish women

Ambulatory blood pressure

Work Ambulatory SBP – cohort – stronger effect for low status
jobs (e.g., waiters) out of 6 job titles in Sweden

Work Ambulatory Blood Pressure, Risk of hypertension – stronger effect for New York City men with 12 years or less of education

Studies of Job Strain and Cardiovascular Disease (Or CVD Risk Factors) Which Stratify by Age

(“new” indicates articles published since the Ann. Rev. Pub. Health article by Schnall et al., 1994, was published; reference numbers are from the review article)

Cardiovascular disease

CVD – cohort – stronger effect for older Swedish white-collar men

CHD symptoms – cross-sectional – stronger effect for older Swedish white-collar workers

CHD – cohort – stronger effect for older women

Ambulatory blood pressure

Work Ambulatory SBP –
stronger effect for older New York City men

Studies of Job Strain and Cardiovascular Disease (Or CVD Risk Factors) Which Stratify by Social Support

(“new” indicates articles published since the Ann. Rev. Pub. Health article by Schnall et al., 1994, was published; reference numbers are from the review article)

Cardiovascular disease

CVD – cross-sectional – stronger Job Strain effect if low social support

All-cause mortality

Mortality – cohort – weaker high latitude effect if high social support

Mortality – cohort – stronger Job Strain effect if low social support

Ambulatory blood pressure

Work and Home Ambulatory DBP – stronger effect for New York City men with lower social support

Studies of Job Strain and Cardiovascular Disease (Or CVD Risk Factors) Which Stratify by Gender

(“new” indicates articles published since the Ann. Rev. Pub. Health review article by Schnall et al., 1994 was published; reference numbers are from the review article)

Cardiovascular disease

CHD – cohort – stronger effect for women (Framingham, U.S.)

MI (hospitalizations) – cohort – similar effects for men and women (Sweden)

CHD – cohort – similar effects for men and women (Finland)

CHD – case-control – similar effects for men and women (Sweden)

CHD symptoms – cross-sectional – similar effects for men and women (Sweden)

CHD symptoms – cross-sectional – similar effects for men and women (Sweden)

Ambulatory blood pressure

cross-sectional – job strain associated with AmBP only for men (North Carolina)

cross-sectional – job strain associated with AmBP only for men (New York City)

cross-sectional – job strain associated with AmBP for both women and men (North Carolina)

cohort – similar magnitude of association with systolic AmBP for both women and men, p-value >.05 since only 18 women vs 40 men in study (Sweden)

cross-sectional – job strain associated with AmBP for women
[note: while this study did not include males, it is noted since it is one of the 3 studies that have found associations between job strain and AmBP among women]

Smoking

cross-sectional – similar effects for men and women

cross-sectional – shift-work and piece-work associated with smoking only among men (Sweden)

Sedentary behavior

cross-sectional – lack of learning opportunities associated with sedentary behavior for both men and women – psychological work demands associated with sedentary beahvior only among women (Sweden)

Job Strain and Ambulatory Blood Pressure References

Job Strain and Ambulatory Blood Pressure

(“new” indicates articles published since the review article by Schnall et al., 1994 was published; reference numbers are from the review article)

Job Strain and Casual Blood Pressure

(all non-significant associations, except 37)

Reliability of Scales

Reliability of Measures of Job Demands and Job Decision Latitude

(“new” indicates articles published since the review article by Schnall et al., 1994 was published; reference numbers are from the review article)

In most studies where scale reliability is reported, coefficient alpha for job demands and job decision latitude is above .70. In the New York City ambulatory blood pressure study the following values were reported for men at Time 1 for job demands, job decision latitude, workplace social support, and their components:

In addition, Job Content Questionnaire scale reliabilities (coeffecient alpha) in a major cross-sectional study in Japan are included in:

Four studies from Sweden as well as one from Australia and one from the U.S. have also reported values for scale reliability using a variety of scale items. These studies are:

In the U.S., many studies have used the basic set of 14 items from the U.S. Quality of Employment Surveys to measure job demands (5 items) and job decision latitude (9 items). One of these studies, in addition to the New York City ambulatory blood pressure study, used subjects’ individual self-reports to measure job characteristics:

Many other U.S. studies have applied national averages of job characteristics by job title from the U.S. Quality of Employment Surveys. U.S. studies of CHD using this procedure are:

U.S. CHD risk factor studies using this procedure are:

Scale reliability information for scales developed from the U.S. Quality of Employment Surveys is reported in:

Since few studies have measured job characteristics at more than one point in time, our study at Cornell is one of the few studies (other than QES) which can provide test-retest reliability. In our sample , among men, over three years, test-retest reliability was r=0.64 for both job demands and job decision latitude — and that includes people who changed job titles (data in paper under review).

Job Strain Scales

The job strain measure is derived from the Job Content Questionnaire. This is a 42-item questionnaire developed by Robert Karasek, MD, PhD, based, in part, on questions drawn from the US Department of Labor/University of Michigan Quality of Employment Surveys. Two scales are used to define job strain-decision latitude and psychological demands.

The first scale, decision latitude, is defined as the sum of two subscales given equal weight:

Skill discretion, measured by six items (keep learning new things, can develop skills, job requires skills, task variety, repetitious, and job requires creativity), and decision authority, measured by three items (have freedom to make decisions, choose how to perform work, and have a lot of say on the job).

The second scale is psychological job demands, defined by five items (excessive work, conflicting demands, insufficient time to work, work fast, and work hard). All questions are scored on a Likert scale of 1 to 4, and psychological demands ranges from 12 to 48 while decision latitude ranges from 24 to 96. (In published papers from the Cornell Blood Pressure Study, a slightly different formula was used to compute the decision latitude scale score, in which the score was not multiplied by 2. Therefore, in papers from the Cornell study, the decision latitude score ranges from 12 to 48.)

The Job Content Questionnaire is copyrighted. Further information regarding the Job Content Questionnaire (referred to as the JCQ) including permission for its use and instructions for scoring, please visit their website.

Job Content Questionnaire Items

Items from the Job Content Questionnaire often used to define psychological job demands and job decision latitude

Psychological job demands

1. My job requires working very fast
2. My job requires working very hard
3. I am not asked to do an excessive amount of work*
4. I have enough time to get the job done*
5. I am free from conflicting demands that others make*

Job decision latitude (the sum of two equally weighted subscales)

Decision authority

1. My job allows me to make a lot of decisions on my own
2. On my job, I have very little freedom to decide how I do my work*
3. I have a lot of say about what happens on my job

Skill utilization

1. My job requires that I learn new things
2. My job involves a lot of repetitive work*
3. My job requires me to be creative
4. My job requires a high level of skill
5. I get to do a variety of different things on my job
6. I have an opportunity to develop my own special abilities

*Reverse scored

Job Strain Quadrant Graphic

The reference for the following graphic is: Landsbergis PA, Schnall PL, Schwartz JE, Pickering TG, Warren K. The association of ambulatory blood pressure with alternative forms of job strain. Scand J Work Env Health; 20:349-63,1994.

Quadrant term

Quadrant formed by dichotomizing latitude and demands scores at the medians of the current sample (latitude <74 and demands >32).

Quadrant term using national means

Area formed by using national (U.S. QES) means for latitude and demands (latitude <72.6 and demands>30.6 for males: latitude <65.7 and demands > 31.3 for females).

Quotient term

Sample demands divided by latitude. This continuous form of the variable can be dichotomized at an arbitrary cutpoint.

Linear term

Linear function created by y=(b) demands-(c) latitude. (If both variables are on the same scale, y=(0.5) demands – (0.5) latitude.) This continuous form of the variable can be dichotomized at an arbitrary cutpoint.

Note: The cutpoints for job decision latitude listed above reflect corrections made for the U.S. QES means for the job decision latitude scale score in December 2000. In addition, the cutpoints for job decision latitude listed above are based on the formulas in the Job Content Questionnaire manual in which the job decision latitude scale score is multiplied by 2. Papers published from the Cornell Blood Pressure Study used a different version of the formula in which the job latitude scale score was not multiplied by 2. Thus, for anyone wishing to compare their findings to the Cornell study findings, do not multiply the job decision latitude by 2and use the following cutpoints: 
1) for the job strain quadrant term based on Cornell sample medians, use latitude <37 and demands >32. 
2) for the job strain quadrant term using national means, use latitude <36.3 and demands >30.6 for males; latitude <32.9 and demands >31.3 for females.

Definitions and Formulations of Job Strain

(All reference, Table and Figure numbers are from: Schnall PL, Landsbergis PA, Baker D. 1994. Job strain and cardiovascular disease. Annu Rev. Public Health 15:381-411. In addition, Figure 2 is from Landsbergis et al., 1994. Association between ambulatory blood pressure and alternative formulations of job strain. Scand J Work Environ Health 20:349-63. Other articles are cited by authors and year and listed at the end of this report.)

Robert Karasek originally developed and provided evidence the “job strain” concept and model. Karasek, writing in 1979, argues that work stress and the resulting physical and mental health effects of work stress, result “not from a single aspect of the work environment, but from the joint effects of the demands of a work situation and the range of decision-making freedom (discretion) available to the worker facing those demands… Job strain occurs when job demands are high and job decision latitude is low” (52, p. 287).

Decision latitude is an operationalization of the concept of control and has often been defined as the combination of job decision-making authority and the opportunity to use and develop skills on the job. (Questionnaire items from the Job Content Questionnaire which have often been used to define job demands and job decision latitude are listed in Table 1.)

The “job strain” model (see Figure 1) states that the combination of high job demands and low job decision latitude will lead to negative physical health outcomes such as hypertension and cardiovascular disease (CVD). In addition, the model contains important predictions regarding the socialization of personality traits and behavior patterns which occurs at work. Chronic adaptation to low control-low demand situations (“passive” jobs in Figure 1) can result in reduced ability to solve problems or tackle challenges, and feelings of depression, or “learned helplessness” (58). Conversely, when high job demands are matched with greater authority and skill use (controllable stressors, or “active” jobs), more active learning and greater internal locus of control develop. This can enable individuals to develop a broader range of coping strategies. The discussion below of formulations of the “job strain” concept will primarily focus on studies of negative physical health outcomes, which have been more thoroughly reviewed.

Joint Statement on the Two Theoretical Models

“Quadrant” model

In order to operationalize the interaction between job demands and job decision latitude that creates “job strain”, the most common procedure in CVD research studies has been to create a dichotomous (“yes”/”no”) “job strain” variable (also called the job strain “quadrant” definition — see Figures 2a and 2b). Study participants are classified as having “job strain” (or “high strain” jobs) if they are above the median or mean on demands and also below the median or mean on decision latitude. Such employees may be identified by dichotomizing self-reports of demands and latitude at either the medians or means of the study sample (Figure 2a) or reference samples such as a national sample (Figure 2b).

However, researchers have not always agreed on the best method to operationalize the interaction between job demands and job decision latitude. Various mathematical forms of “job strain” have been reported with significant results suggesting a certain robustness to the “job strain” concept. However, this may be, in part, an artifact of the usual selection process of reporting positive associations and ignoring negative ones. The following forms (in addition to the “quadrant” model) have been reported:

“Quotient” model

A newer approach, used in seven CVD studies with positive results (32, 108-110, 114, 115, Landsbergis et al., 1994) has been to create a continuous independent variable — demands divided by latitude (figure 2c). This measure can then be dichotomized at an arbitrary cutpoint. Since this quotient term is non-linear, and tends to give more weight to latitude (the denominator) than demands, a similar continuous (but linear) formulation has been proposed in which the contributions of low latitude and high demands are equally weighted (figure 2d) The linear formulation, essentially demands minus latitude, can then also be dichotomized at an arbitrary cutpoint.

In one other study with positive associations between “job strain” and heart disease (59), a similar formulation was used to isolate 20% of the sample as “high strain”. The “high strain” group was defined as (demands + 1) x (latitude – 1) < -1.2, where demands and latitude are standardized scores.

Multiplicative interaction

In six CVD studies (19, 37, 49, 90, 93, Landsbergis et al., 1994), a multiplicative interaction term partialled for main effects (demands x latitude, controlling for demands and latitude) was used. However, in only three of those studies (37, 49, Landsbergis et al., 1994) did the interaction term significantly improve the variance explained by the model beyond what could be obtained with only the main effects.

Graphical approaches

Exploratory graphical approaches have been used (49, 54, Landsbergis et al., 1994) to examine interaction effects and thresholds (non-linear effects). For example, demands and latitude have been divided into tertiles or quartiles, and patterns of heart disease risk or blood pressure elevation examined across the resulting nine (49, Landsbergis et al., 1994) or 16 (54) exposure cells.

Main effects models

A number of CVD studies have examined the main effects of job demands and job decision latitude on risk of illness rather than their interaction. Nineteen (4, 8, 19, 30, 36-38, 49, 53-55, 59, 68, 69, 81, 90, 110, Johansson et al., 1991; Alterman et al., 1994) of 31 studies that examined main effects found some significant associations between job decision latitude and outcome. However, associations between job demands and outcome were significant in only nine (6, 30, 37, 49, 54, 55, 59, Johansson et al., 1991) of 29 studies.

Issues related to the concept of interaction

Research studies have provided some evidence of an interaction between demands and decision latitude in producing increased risk of heart disease and high blood pressure. However, evidence for this interaction in predicting measures of psychological strain such as anxiety and depression have not been consistent. Some researchers (for example, Ganster, 1989) argue that while the main effects of demands and decision latitude are associated with stress outcomes, the interaction between the two is not. Karasek (1989, p. 143) argues that while “a multiplicative interaction would strengthen the plausibility” of the original “job strain” concept, “the practical implications for job redesign are largely unchanged if two separate linear effects for control and demand are observed. Also, an important caveat is that the ability to detect such interactions is severely limited in many ordinary-least-squares analytical techniques…leading to strong possibilities that such interactions are systematically underestimated. However, for the demand-control model, the existence of a multiplicative interaction term is not the primary issue. The primary ‘interaction’ claimed for the model is that two separate sets of outcomes [both physical illness and active learning] are jointly predicted by two different combinations of psychological demands and decision latitude — an interaction of significant practical importance.”

Addition of social support

Workplace social support has also been examined in conjunction with the job strain model in several studies of CVD (50, 8, 25, 49, Hall et al., 1993; Landsbergis et al., 1994) as well as studies of psychological strain outcomes. Evidence has been provided for both a social support main effect (25, 49) and a buffering by social support of the effects of job strain (8, 25, 49). A third approach (50, Landsbergis et al., 1994), which does not try to disentangle main effects and interaction, simply hypothesizes that socially isolated (i.e., without supportive coworkers or supervisors) “high strain” work (“iso-strain” rather than simply “job strain”) carries the highest risk. This approach was proposed since “iso-strain” is a univariate measure, “a more parsimonious instrument for measuring and analyzing workplace conditions” (50, p. 272)

Contrast to other models of work stress

The “job strain” model was not designed to replace the earlier more complex person-environment model of occupational stress originating from the University of Michigan (16, 42) or the recent refinement of the Michigan model by the National Institute for Occupational Safety and Health (NIOSH) (44). The Michigan model incorporates: both perceived and objective stressors; the potential moderating effects of social support, personality factors, non-work factors, and demographic measures; feedback loops; and a wide variety of outcome measures. Issues of self-reported vs. objective job characteristics and effect modification are, of course, also important issues for the “job strain” model. However, the “job strain” model, in contrast to the Michigan model, emphasizes the need to distinguish features of the work environment that can be categorized as demands or control (and does not simply list all job factors as potential stressors), examines the interaction between demands and control, and emphasizes the stress-producing properties of these objective factors, and not solely individual perceptions, or person-environment fit.

References

Alterman T, Shekelle RB, Vernon SW, Burau KD. Decision latitude, psychological demand, job strain and coronary heart disease in the Western Electric Study. American Journal of Epidemiology 1994;139:620-7.

Ganster DC. Worker control and well-being: A review of research in the workplace. In Job Control and Worker Health, eds. SL Sauter, JJ Hurrell, CL Cooper. New York: Wiley, 1989;3-23.

Hall EM, Johnson JV, Tsou T-S. Women, occupation, and risk of cardiovascular morbidity and mortality. Occupational Medicine: State of the Art Reviews 1993;8:709-19.

Johansson G, Johnson JV, Hall EM. Smoking and sedentary behavior as related to work organization. Soc Sci Med 1991;32:837-846.

Karasek RA. Control in the workplace and its health-related aspects. In Job Control and Worker Health, eds. SL Sauter, JJ Hurrell, CL Cooper. New York: Wiley, 1989;129-159.

Landsbergis PA, Schnall PL, Warren K, Pickering TG, Schwartz JE: Association between ambulatory blood pressure and alternative formulations of job strain. Scand J Work Environ Health 1994;20:349-363.

CSE Education Activities for 2010

CSE Staff and Consultants teach a Work and Health Course at UCLA one semester each year and have, over the last ten years, provided over 100 students with skills on conducting surveillance at the workplace and measurement of exposures and outcomes such as blood pressure.

The CSE sponsors a number of education activities including 1) a course at UCLA (Work and Health), 2) a course at UCI of Occupational Cardiology, 3) conferences and workshops in international settings, and 4) regular meetings of the  California Work and Health Study Group (last held this past May 2010 in Berkeley).

The Center is involved in the preparation and publication of scientific articles and books. CSE is proud to have had two books published during the past decade each with over 30 internationally recognized authors; the first, The Workplace and Cardiovascular Disease published by Hanley and Belfus in 2000 and the second, Unhealthy Work: Causes, Consequences, Cures published by Baywood in 2009. In 2010 book parties were held in Los Angeles and Berkeley to promote Unhealthy Work at which several of the books editors gave presentations.

The Center is excited to have just had Unhealthy Work translated by colleagues into Korean and Spanish. The Korean version was published in September 2010, Seoul, Korea by GyeChuk Mun Wha Sa (Publisher) while the University de Los Andes in Bogota, Colombia is publishing the Spanish version edited by Dr. Viviola Gomez, Department of Psychology.

During 2010, CSE consultants have prepared multiple abstracts, some based on a pilot web survey of Orange County Fire Authority (OCFA) firefighters conducted with colleagues at the UCI COEH. Several abstracts were accepted as oral presentations, a few others as poster presentations at the 4^th International Conference of Occupational Health (ICOH) Work Organization and Psychosocial Stressors (WOPS) conference in Amsterdam in June 2010.

Paul Landsbergis, consultant to the CSE, with Peter Schnall, recently published a book chapter on job strain and cardiovascular disease for the second edition of the Handbook of Occupational Health Psychology. He is in the process of working on several new manuscripts, including a meta-analysis of job strain and ambulatory blood pressure (in collaboration with Marnie Dobson and Peter Schnall of the CSE) and a study of job strain and masked hypertension. Additionally, Paul authored papers for the 2010 Global Obesity Summit recently held in Jackson, Mississippi.

BongKyoo Choi, consultant to the CSE, published papers on work and obesity during 2010 in the American Journal of Industrial Medicine and the International Journal of Occupational Medicine and Environmental Health.. His other research on work and obesity using a US national dataset was well received at the 2010 ICOH-WOPS conference in Amsterdam, the Netherlands (Best Abstract Award and 2010 Global Obesity Summit, Jackson, MS (New Investigator Travel Award). In addition, he submitted a critical commentary to NIH on their draft strategies for research into obesity.

The Center also considers the education of the public one of its main goals. To support this aim, the Center’s Informations Systems Manager (ISM), Erin Wigger, moderates a network of health professionals through several listservs and manages a website using web design software (Dreamweaver).

Expansion of the ISM’s role at the Center includes broadening the Center’s fundraising efforts, the redesign of the Center’s Job Stress Network website as well as the creation and development of a blog and new website based on the Center’s recently published book, Unhealthy Work: Causes, Consequences, Cures, Baywood, 2009. This website represents the first of the Center’s efforts to begin presenting information on work and health to the lay-public.

Workplace Stressors

A wide range of workplace conditions have been implicated as risk factors for a variety of health problems. These workplace conditions include shift work, long work hours, psychosocial stressors, as well as physical conditions.

Health Consequences

Occupational groups exposed to a large number of work stressors are found to be at high risk for hypertension, cardiovascular disease, stroke, peptic ulcer disease, headache, musculoskeletal disorders, burnout, depression, anxiety and other undesirable outcomes.