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Investigation of Work History

Investigation of Work History – To Measure Cumulative Exposure


In most research studies, “job strain” was only measured at one point in time (Schnall, Landsbergis & Baker, 1994). Yet, it is believed that cumulative exposure to “job strain” increases risk of hypertension or CHD. Most likely it is the chronic biological arousal due to sustained “job strain” that contributes to the development of essential hypertension (Schnall, Landsbergis & Baker, 1994). If duration of exposure to “job strain” is not measured, then we cannot determine whether the stressful work environment has existed for the person for only the previous month, or for the previous 40 years. Use of current exposure as a surrogate for lifetime exposure is inaccurate, in part, since people often gain skills with time and age, may be promoted, may select out of “high strain” jobs, or their job characteristics may change even within the same job title. For example, in the Cornell study, 22% of the study participants changed “job strain” status over the course of 3 years (Landsbergis et al., 1995). Many study participants with a lengthy history of “job strain” might thus be currently classified as “non-strain” because of recent promotions or other job changes. Use of inaccurate measures of exposure to “job strain” (i.e., non-differential misclassification) can bias results towards the null hypothesis, leading to the conclusion that the effect of “job strain” on blood pressure is weaker than it truly is.

A work history interview, developed by Paul Landsbergis for the Cornell ambulatory blood pressure study, included two questions each on job demands, decision latitude and social support. These questions were asked of the study participant for each past job held. Interviews of 284 cohort study participants (who reported a total of 1,366 jobs), were completed as of 1/1/95. All subjects participating in the third round of data collection agreed to the interviews. Eligible interview subjects included 212 men enrolled in the cohort study at Time 1, 6 men enrolled at Time 2, 21 women enrolled at Time 1 and 45 women enrolled at Time 2. In addition, 100 nurses and aides, newly enrolled in the study at time 3, have completed a questionnaire version of the work history interview.

For the 284 completed interviews, internal consistency of the three two-item scales was acceptable (workload demands, a=.81; job decision latitude, a=.62; workplace social support, a=.63). In order to increase the reliability of the critical job decision latitude scale, two items were added to the questionnaire: “the freedom to decide how you do your work” was added to the decision-making authority subscale; “the chance to be creative” was added to the skill utilization subscale. Thus, the decision latitude of each past job is now measured by four items. Among the 155 subjects who have answered all 4 latitude items, scale reliability has increased to a=.83.


Work History Questionnaire

Listed below are questionnaire items used to define job demands, job decision latitude and workplace social support for each past job in the Work History Questionnaire used in the Cornell study. “On that job, did you have….

A) Psychological Job Demands

1) To work very hard
2) An excessive amount of work

B) Job Decision Latitude

Decision Authority
1) The freedom to decide how you do your work
2) A lot of say about what happens on the job
Skill Utilization
3) The chance to be creative
4) A high level of skill

C) Workplace Social Support

Coworker Support
1) Helpful coworkers
Supervisor Support
2) A helpful supervisor


Data Analysis

Measures of cumulative exposure to be analyzed are based on recent research by Jeffrey Johnson and colleagues (Johnson et al., 1991; Johnson & Stewart, 1993). They used Swedish national data bases to compute average job demands, control (latitude) and support scores for each year of a person’s work history, based upon their job title, age, gender and years of employment. In order to determine the effects of total work history exposure, as well as the time course of exposure (whether earlier or later exposure affects outcome), they constructed both discrete and cumulative 5-year exposure windows. Thus, mean job characteristics scores in each of the following time periods were analyzed for association with future CVD:

  1. Discrete: 1-5 years prior to outcome, 6-10 years, 11-15 years, 16-20 years, 21-25 years, 26+ years.
  2. Cumulative: 1-10 years prior to outcome, 1-15 years, 1-20 years, 1-25 years, total work history.
    In addition, to further assess patterns of occupational movement (career trajectory), Johnson et al. (1991) and Johnson & Stewart (1993) analyzed the following exposure measure for association with future CVD:
  3. Direction of change: Whether job characteristics significantly increase, decrease or remain stable over the working life.

In the Swedish study, exposure among men to low control jobs, within the previous 25 years, was prospectively associated with CVD mortality (Johnson et al., 1991). Higher risk was observed among blue-collar men.


References

Johnson JV, Hall EM, Stewart W, Fredlund P, Theorell T. Combined exposure to adverse work organization factors and cardiovascular disease: Towards a life-course perspective. In Fechter L, ed. Proceedings of the Fourth International Conference on the Combined Effects of Environmental Factors, Baltimore: Johns Hopkins University, 1991:117-121 .

Johnson JV, Stewart W. Measuring work organization exposure over the life course with a job-exposure matrix. Scand J Work Environ Health 1993;19:21-28.

Landsbergis PA, Schnall PL, Schwartz JE, Warren K, Pickering TG. Job strain, hypertension and cardiovascular disease. In Organizational Risk Factors for Job Stress, eds. SL Sauter, LR Murphy. Washington, DC: American Psychological Association 1995:97-112.

Schnall PL, Landsbergis PA, Baker D. Job strain and cardiovascular disease. Ann Rev Public Health 1994;15:381-411.

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