INSERM Unité 360, Paris, France
INSERM U88, Paris, France
INSERM U558, Toulouse, France
Georges Pompidou European Hospital, Paris, France
Correspondence: Sabrina Paterniti, INSERM U360, Hôpital de la Salpêtrière, 84 Bd de l'Hôpital, 75651 Paris CEDEX 13, France. Tel: +33 01 0142162554; fax: +33 01 0142162541; e-mail: paternit{at}chups.jussieu.fr
Funding detailed in Acknowledgements.
See editorial, pp.
9698, this issue.
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ABSTRACT |
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Aims To examine the relationship between psychosocial factors at work and changes in depressive symptoms, taking into account personality traits.
Method The role of occupational characteristics, psychosocial stress and personality traits in predicting an increase of depressive symptoms was evaluated in 7729 men and 2790 women working at the French National Electricity and Gas Company, with a 3-year follow-up.
Results In men, high decision latitude was predictive of a decrease in the Centre for Epidemiologic Studies Depression scale (CESD) scores. In both genders, high job demands and low social support at work were predictive of increased scores, irrespective of personality traits and covariates.
Conclusions Adverse psychosocial work conditions are predictors of depressive symptom worsening, independent of personality traits.
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INTRODUCTION |
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METHOD |
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Depressive symptoms
In 1993 and 1996, the French version of the Center for Epidemiologic
Studies Depression scale (CESD;
Radloff, 1977;
Fuhrer & Rouillon 1989)
was sent to the subjects to assess depressive symptoms. The CESD is a
20item self-report of depressive symptoms experienced in the past week.
Each item is rated from 0 to 3 (0=rarely; 1=some of the time; 2=occasionally;
3=most of the time); the total score ranges from 0 (no depressive symptom) to
60. The CESD scale has been used widely in epidemiological studies.
Psychosocial factors at work
In 1995, the self-administered questionnaire included 16 items concerning
the psychosocial aspects of work. Details of this questionnaire are published
elsewhere (Niedhammer et al,
1998). In brief, items were selected from two sources
(Karasek, 1979;
Johnson & Hall, 1988) as
being particularly suitable for measuring job stress in a heterogeneous
population. Three psychosocial work factors assessed the main components on
the job strain model: psychological demands (a five-item indicator measuring
job demands, time pressure and conflicting demands); decision latitude (a
six-item indicator measuring the subject's influence on or control over his or
her work, job variety, and the possibilities for learning new skills); and
social support at work (a five-item indicator measuring contacts with
co-workers during work and leisure).
Personality traits
In 1993 the subjects of the GAZEL cohort were sent a set of three
psychosocial questionnaires designed to evaluate the role of personality
traits in the risk of morbidity and mortality.
The Bortner scale (Bortner, 1969) and the Seeman and Syme scale (Seeman et al, 1995) were used to assess, respectively, pattern A behaviour and self-esteem. Both the Bortner scale and the Seeman and Syme self-esteem scale consist of 14 bipolar items graduated from 1 to 6; their scores range from 14 to 84. The Buss and Durkee Hostility Inventory (Buss & Durkee, 1957) consists of 75 true/false items and give rise to the computation of eight sub-scores: assault, verbal hostility, indirect hostility, irritability, negativism, suspicion, resentment and guilt. The sum of the first seven sub-scales leads to a total hostility score.
Occupational characteristics
In 1990, the questionnaire included questions about working hours and
exposure to six physical workload factors: standing for long periods; work in
uncomfortable positions; long, frequent or fast walking; handling or lifting
heavy weights; use of vibrating tools; and the use of a computer screen.
Workers belonged to one of three occupational grades: low (clerks and blue-collar workers); intermediate (technicians and associated professionals); and high (professionals, managers and engineers). Occupational grade was indicated by the personnel department of the company and was studied for the year 1993.
Four of the stressful events included in the 1993 questionnaire concerned occupational situations occurring in the previous 12 months (job change, transfer, reconversion and departmental restructuring).
Potential confounding factors
Data were obtained by the self-administered questionnaire for 1993
concerning the following items: age; gender; marital status (married or
cohabiting, single, divorced or widowed); stressful personal events during the
previous year (admission to hospital or accidents); and the presence of one or
more chronic diseases (asthma, infarction, angina, hypertension, diabetes,
osteoarthritis, hypercholesterolaemia or cancer).
Information about monthly family income (tertiles of distribution were < [UNK]2000, [UNK]2000-2600 and > [UNK]2600) and educational level (primary, secondary or university) were collected at the beginning of the study, in 1989.
Statistical analysis
Separate analyses were performed for men and women.
We considered 1993 as the baseline evaluation and 1996 as the 3-year followup evaluation. We defined change in the CESD score as the difference between the scores for 1996 and 1993. Psychosocial factors at work and personality traits were used as continuous variables in all the analyses.
The relationship between occupational characteristics and the change in CESD score was tested by covariance analysis, adjusting for baseline CESD score. The relationship between personality traits, psychosocial factors at work and CESD scores in 1993 was tested by Spearman's rank correlation coefficient because of the skewed distribution of CESD scores. The relationship between the above variables and the change in CESD score was tested by partial correlation analysis, adjusted for baseline CESD score. The correlation between personality traits and psychosocial factors at work was evaluated by Pearson's coefficients.
Hierarchical linear regression analyses were used to ascertain whether psychosocial factors at work are predictive of an increase in the CESD score, after adjustments for personality traits, occupational factors (occupational grade, stressful occupational events, working hours and physical workload factors) and covariates (age, education, income, marital status, stressful personal events and the presence of one or more chronic diseases). Three blocks of variables were entered. In the first block, change in CESD scores was regressed on occupational factors and covariates. Psychosocial factors at work and personality traits were added respectively to the second and third blocks. Improvement of fit was tested by the F-test.
Analyses were carried out using SAS software (release 6.12; SAS Statistical Institute, Cary, North Carolina, USA).
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RESULTS |
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Comparison of participants and non-participants
Socio-demographic characteristics and baseline depression scores were
compared for subjects included in the analysis and those who were not. The
rate of participation was lower among women, single or cohabiting subjects,
those with low incomes and those with at least one physical workload factor, a
low educational level and a low occupational grade. Participants were slightly
older than non-participants and had lower baseline CESD scores.
Characteristics of the sample
Men and women differed for all the socio-demographic, occupational and
psychosocial factors studied, as well as for CESD scores and
personality traits (Table
1).
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Socio-demographic and work characteristics and change in CESD
scores
For both genders low family income, and for women an accident or admission
to hospital during the previous 12 months, were associated with an increase in
the CESD score, after adjustment for baseline CESD scores. In
men, age was negatively and significantly correlated with the change in
CESD score; in women, the correlation was also negative but was not
significant. The presence of a chronic disease was predictive of a CESD
increase in men. Marital status and educational level were not associated with
CESD change.
Subjects belonging to the lowest occupational grade had the largest CESD score increase, as well as those who had experienced a stressful occupational event in the previous 12 months. The number of physical workload factors was predictive of the CESD score increase, as experiencing a stressful occupational event in the previous 12 months. Working hours were associated with an increase in the CESD score for men only (Table 2).
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Psychosocial factors at work, personality traits and CESD
scores
In both genders, decision latitude, social support at work and self-esteem
were predictive of a decrease in the CESD score, and job demands, total
hostility and pattern A behaviour of an increase in this score
(Table 3).
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Table 4 shows the correlations between personality traits and psychosocial factors at work. Although statistically significant, the coefficients were low.
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Multiple linear regressions
In the first step of linear regression analysis, we tested the effects of
occupational characteristics on CESD score increases, after adjustment
for the baseline CESD score, and other covariates
(Table 5). For both men and
women, occupational grade, stressful occupational events and the number of
physical workload factors were predictive of an increase in CESD
scores. In the second step, psychosocial factors at work were added to the
model. High job demands and low social support at work were associated with
increase in CESD score between 1993 and 1996 for both genders. In men,
high decision latitude was associated with a decrease in CESD scores.
Finally, personality traits were added to the model. Self-esteem and total
hostility were significantly predictive of a CESD change. The
predictive effects of psychosocial factors at work remained significant after
the inclusion of personality traits.
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Because of the weak but significant correlations between personality traits and the three dimensions of job stress, we performed collinearity analysis using the SAS PROC REG (option COLLIN) procedure for multivariate linear regression. This analysis did not detect collinearity problems.
Finally, we tested possible interactions between each personality trait and each job stress factor included in the study of CESD change. In men, significant inter-actions were found between decision latitude and total hostility (B= -0.009 (s.e.=0.003), P=0.005) and between social support at work and self-esteem (B= -0.01 (s.e.=0.004), P=0.005). Among hostile men, decision latitude was associated with a larger decrease in the CESD score than in non-hostile men. In addition, among men with low self-esteem, low social support at work was related to a larger increase in CESD score.
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DISCUSSION |
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Psychosocial factors at work influence subsequent affective
symptoms
Our findings are in agreement with those of previous longitudinal studies
showing that job stress influences subsequent affective symptoms. Thus, in a
sample of 325 male employees followed-up for 1 year, Bromet et al
(1988) found that job demands
were predictive of affective disorders (an episode of depression or a
generalised anxiety disorder), whereas co-worker support seemed to decrease
this effect. Niedhammer et al
(1998) found that high
psychological demands and low decision latitude and social support at work
were associated with subsequent high depressive symptoms. Kawakami et
al (1992) found that job
unsuitability and poor human relations in the workplace were risk factors for
depressive symptoms 2 and 3 years after the baseline evaluation.
In our study we considered three personality traits that could affect psychosocial factors at work and/or could be associated with depressive symptoms. Subjects with low self-esteem can drift into jobs in which they have little control over decision-making. Personality traits such as hostility and pattern A behaviour can directly affect the choice of work or modify the work environment (Miller et al, 1996), and could also influence perception of both depressive symptoms and psychosocial factors at work.
The strength of the association between psychosocial factors at work and increase of depressive symptoms was not altered in our study by introducing measures involving personality traits into multivariate models. Our results are in agreement with one cross-sectional study which found that cynicism and hostility did not alter the relationship between psychosocial work conditions and psychological distress (Bourbonnais et al, 1996). Kawakami et al (1992) found a similar result when the type A behaviour pattern was included among the covariates in a longitudinal analysis of the effects of psychosocial factors at work on depressive symptoms.
In the female sample studied here, decision latitude was not associated with a CESD score increase when other covariates, particularly occupational grade, were taken into account. However, as occupational grade strongly affected psychosocial factors at work, the true association between psychosocial factors at work and depressive outcome could have been under-estimated by adjusting for grade (North et al, 1996).
Personality traits and depressive symptoms
In our study, self-esteem and total hostility were independent predictors
of an increase of depressive symptoms. Lowered self-esteem is a
well-recognised symptom of depressive illness and a prognostic factor in
patients with depression (Andrew et
al, 1993; Sherrington
et al, 2001). However, it is unclear whether low
self-esteem predicts the onset of depressive disorders in the general
population. Hokanson et al
(1989) found that low
self-esteem pre-disposed individuals to subsequent general psychopathology,
including depression. Some community surveys showed that low self-esteem does
predict future episodes of depression in conjunction with other factors, such
as environmental stressors or prior psychiatric consultations
(Brown et al, 1986;
Ingham et al, 1987).
In a prospective study Roberts & Kendler
(1999) suggest that
neuroticism could explain the association between self-esteem and the risk of
major depression. To our knowledge, there is no empirical literature on the
role of hostility in increasing risk of depression, although studies have been
published showing an association between the two dimensions
(Schless et al,
1974).
Psychosocial factors at work and personality traits
Interestingly, low self-esteem and high hostility were both associated, in
our study, with high job demands, low decision latitude and low social support
at work, that is with dimensions known to be stressors at work. So, our
results seem in agreement with those of Williams et al
(1997), who found that
psychosocial factors at work and dimensions of psychological distress cluster
together. Our findings lead to the hypothesis that the same individuals
suffering from low self-esteem and/or high hostility are perceiving high job
strain conditions at work, that is the same individuals do have personality
and work factors that increase the risk of developing depressive symptoms.
However, causal direction between psychosocial factors at work and personality
traits may not be defined on the basis of our data. Work status is known to
have an impact on self-esteem (Andrews
& Brown, 1995) and personality traits could influence
perception of job strain.
We found some interactions between personality traits and the psychosocial factors at work in increasing depressive symptoms. Similarly, Stansfeld et al (1999) found that adjustment for hostility decreased the effect of job demands on psychiatric disorders in men.
Limitations of the study
Our study had some limitations. As our group only consisted of
participants, there could have been a selection bias. In addition, subjects
not included in the analyses had more depressive symptoms and more job stress
factors at baseline than subjects that were included, thus suggesting a
healthy worker effect, i.e. that subjects selected had fewer depressive
symptoms and fewer job stress factors. This selection bias might have
decreased the strength of the relationship between risk factors (job stress
factors) and morbidity (CESD score increase).
Two other potential biases could have limited our conclusions about the possible causal effects of psychosocial factors at work on the increase of the severity of depressive symptoms. First, we did not use a full two-wave panel design, as only one evaluation of psychosocial stress factors at work was available. Therefore, we were unable to test reciprocal causal relationships. Second, both exposure and outcome were measured by subjective means, i.e. self-evaluation. Subjects with depression report work conditions in a more negative manner than non-depression subjects do.
In our study, we had no objective measurement for the psychosocial work environment and we could not establish whether objective conditions had caused the perception of high stress at work. However, some studies indicate that self-reports of job stress are stronger predictors of health outcomes than objective indexes of job stress (Hammar et al, 1994). On the basis of the results of our study, we could hypothesise that the perception of high stress at work leads to an increase of depressive symptoms. However, it is not possible to exclude the possible presence of the following vicious cycle: being depressed handicaps coping and further impairs role functioning, thus increasing perceived job stress, which in turn increases depression.
Clinical implications
Psychosocial stress factors at work are predictive of an increase in the
CESD score. Interventions designed to reduce perception of excessive
job demands and increase the degree of perceived decision latitude or social
support could slow down the development of depression. In addition, our
results suggest that better knowledge of the interactions between personality
traits and job stress factors might be helpful for the choice of more
effective interventions.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication August 2, 2001. Revision received January 16, 2002. Accepted for publication February 17, 2002.
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