Journal of Occupational Health Psychology
April 1999 Vol. 4, No. 2, 95-107
© 1999 by the Educational Publishing Foundation
For personal use only--not for distribution.
Job Strain and Evolution of Mental Health Among Nurses
Renée Bourbonnais
Department of Rehabilitation Laval University
Monique Comeau
Department of Rehabilitation Laval University
Michel Vézina
Department of Rehabilitation Laval University
ABSTRACT
The objective of this 2nd phase of a 2-year study among female nurses was to provide
further empirical validation of the demands—control and social support model. The
association of job strain with psychological problems and the potential modifying role
of social support at work were examined. A questionnaire was sent at the workplace
to 1,741 nurses. The same associations were found between psychological demands,
decision latitude, and a combination of the 2 with psychological distress and
emotional exhaustion for current exposure and for cumulative exposure. Social
support had a direct effect on these psychological symptoms but did not modify their
association with job strain. Longitudinal and prospective data are needed to study the
occurrence and persistence of health problems when exposure is maintained or
retrieved.
Health professionals in the United States have higher than expected rates of suicide
and alcohol and drug abuse, higher rates of hospital admission from mental disorders,
and elevated admission rates to mental health centers ( Sauter, Murphy, & Hurrell,
1990 ). French researchers have reported that among female hospital workers (43%
nurses), 26% of participants had a high score on the General Health Questionnaire,
indicating an elevated risk for minor psychiatric morbidity. Moreover, 32% declared
fatigue, 31% sleep impairment, and 28% drug use (antidepressants, sedatives, or
sleeping pills), and 21% had a psychiatric diagnosis at a routine medical visit (mostly
depressive state or irritability; Estryn-Behar et al., 1990 ). A cross-sectional study of
nurses from one hospital in the province of Quebec, Canada, in 1990 revealed that
29.8% reported symptoms of high psychological distress and 21.8% reported a work
inhibition syndrome ( Préville, Beauchemin, & Potvin, 1991 ). In our own study
among 1,891 nurses in 1994, high psychological distress was declared by 28.3% of
the participants compared with 25.5% in the Quebec working population in 1992—
1993 ( Santé Québec, Bellerose, Lavallée, Chénard, & Levasseur, 1995 ), and 8.4%
had a high score on the three dimensions of the Maslach Burnout Inventory.
Job Strain and Social Support at Work
It is now recognized that certain characteristics of the work environment may
contribute to the incidence of mental health problems among workers ( Vézina,
Cousineau, Mergler, Vinet, & Laurendeau, 1992 ). The three most studied
characteristics of the work environment in relation to health are job demands, job
latitude, and social support. Karasek's job strain model postulates that health
problems, both physical and psychological, are associated with job strain that results
from the combination of high psychological demands and low decision latitude at
work ( Karasek & Theorell, 1990 ). Social support, which refers to helpful social
interaction available on the job from coworkers and supervisors, is hypothesized to
reduce the effect of job strain on health ( Johnson, Hall, & Theorell, 1989 ; Karasek &
Theorell, 1990 ).
The effects of job strain on cardiovascular diseases have been observed in several
studies ( Kasl, 1996 ; Schnall, Landsbergis, & Baker, 1994 ). There is, however,
conflicting evidence on the association between job strain and mental health in
different populations ( Braun & Hollander, 1988 ; Carayon, 1993 ; Cree & Kelloway,
1993 ; De Jonge, Janssen, & Van Breukelen, 1996 ; Karasek & Theorell, 1990 ;
Landsbergis, 1988 ; Landsbergis, Schnall, Deitz, Frieman, & Pickering, 1992 ; Parkes,
1991 ; Stansfeld, North, White, & Marmot, 1995 ), and Karasek's model raises some
criticism ( Kristensen, 1995 ; Muntaner, Eaton, & Garrison, 1993 ; Parkes, 1991 ;
Söderfeldt et al., 1997 ; Wall, Jackson, Mullarkey, & Parker, 1996 ). These
discrepancies in results may be due to (a) the different populations studied
(homogeneous or heterogeneous); (b) different methodologies (cross-sectional or
longitudinal studies, self-reported or external measures of job strain, diverse measures
of exposure or outcome, the lack of control for confounders or effect modifiers); or
(c) varying statistical procedures used and lack of power to detect a significant risk in
certain studies.
In a previous study of white-collar workers, we found a significant association
between job strain and psychological distress ( Bourbonnais, Brisson, Vézina, &
Moisan, 1996 ). In that study, although social support at work had a direct effect on
psychological distress, it did not modify the association between job strain and
psychological distress ( Bourbonnais et al., 1996 ).
Job Strain, Social Support at Work, and Psychological Disorders
Among Nurses
Among nurses, several studies found an association between psychological disorders
and job demands or workload ( Bourbonnais, Vinet, Meyer, & Goldberg, 1992 ;
Bourbonnais, Vinet, Vézina, & Gingras, 1992 ; Constable & Russell, 1986 ; EstrynBehar et al., 1990 ; Fong, 1993 ; McCranie, Lambert, & Lambert, 1987 ; Oehler,
Davidson, Starr, & Lee, 1991 ), job latitude ( Parkes, 1982 ; Petterson, Arnetz, &
Arnetz, 1995 ), and social support at work ( Browner, 1987 ; Constable & Russell,
1986 ; Fong, 1993 ; Oehler et al., 1991 ; Ogus, 1990 ; Parkes, 1982 ; Revicki & May,
1989 ; Singh, 1990 ). Three studies have documented the association of job strain and
burnout or somatic symptoms among health care professionals ( De Jonge et al., 1996
; Landsbergis, 1988 ; Parkes, Mendham, & Von Rabenau, 1994 ). Landsbergis
reported a significant association between both high job demands and low job
decision latitude and depression, the emotional exhaustion component of burnout,
sleep disturbances, and physical symptoms in health care workers. An association
between job strain–a combination of high demands and low latitude–and emotional
exhaustion was also found in that study ( Landsbergis, 1988 ). De Jonge et al. reported
that high levels of autonomy at work attenuate the increase of emotional exhaustion
due to job demands ( De Jonge et al., 1996 ). The authors also reported that low job
demands and a high amount of work-related support seem to reduce feelings of
exhaustion among health care professionals. Only one study among a sample of health
care workers found some evidence that the interactive effects of job demands, control,
and social support at work significantly predicted somatic symptoms ( Parkes et al.,
1994 ). In that study, high job strain was associated with high somatic scores only
when support was low, whereas low job strain was associated with low symptom
levels irrespective of support level. No other study documented the modifying effect
of social support at work on the association between job strain and mental health in
nurses.
First Phase of 2-Year Prevalence Study
In the first phase of our study among nurses in 1994, we observed an association
between job strain and psychological distress and emotional exhaustion (
Bourbonnais, Comeau, Dion, & Vézina, 1998 ). However, exposure to either high
psychological demands or low job decision latitude was also associated with an
elevated level of psychological distress and emotional exhaustion. There was a
multiplicative effect of the combination of high psychological demands and low
decision latitude for psychological distress and an additive effect for emotional
exhaustion. The association among job strain, psychological distress, and emotional
exhaustion remained significant even after adjusting for potential confounders: age,
hospital seniority (for emotional exhaustion only), number of hours worked per week,
social support at work and outside of work, Type A behavior, and stressful life events
in the last 12 months: odds ratio (OR) = 2.34 (1.62—3.36) for psychological distress
and OR = 5.77 (3.92—8.50) for emotional exhaustion. Social support at work was
significantly associated with psychological distress and emotional exhaustion.
However, this negative association did not modify the association between job strain
and these psychological symptoms.
Other Risk Factors
Other risk factors in the psychosocial work environment may influence nurses' mental
health: the work unit and the type of patients ( Bourbonnais, 1985 ; Dewe, 1988 ),
work status ( Bourbonnais, Vinet, Meyer, & Goldberg, 1992 ), current position (
Leppanen & Olkinuora, 1987 ), and work schedules ( Estryn-Behar et al., 1990 ;
Skipper, Jung, & Coffey, 1990 ). Moreover, the effects of work stressors vary from
one individual to another. It is therefore important to control for personality factors
such as Type A behavior ( Arsenault & Dolan, 1983 ; Dompierre, 1989 ; Préville et
al., 1991 ) and factors outside the formal work environment to show the independent
effect of psychosocial constraints at work on health. Factors outside of work that have
to be taken into account include recent stressful life events ( Avison & Turner, 1988 ;
Ivancevich, 1986 ); domestic load, which adds to overall workload ( Barnett,
Davidson, & Marshall, 1991 ; Skipper et al., 1990 ; Tierney, Romito, & Messing,
1990 ); and social support from family and friends, which may have a buffering effect
against health problems ( Fong, 1990 ; House, Landis, & Umberson, 1988 ; Revicki &
May, 1989 ).
Objective of Second Phase of the Study
The objective of the second phase was to provide further empirical validation of the
demands—control and social support model. The specific objectives were to
determine (a) whether a current exposure to job strain, defined as high psychological
demands and low decision latitude, was associated with a higher prevalence of
psychological distress and emotional exhaustion among nurses, and (b) whether a
cumulative exposure to job strain was associated with higher prevalence of
psychological distress among nurses. A secondary objective was to determine if social
support at work modified these associations.
Method
Participants
All female nurses with permanent status employed in six acute care hospitals in the
province of Quebec, Canada, were asked to participate in a 2-year study on
psychosocial factors and mental health. A self-reported questionnaire was distributed
on two occasions: during spring 1994 (Time 1 or T1) and during fall 1995 (Time 2 or
T2). 1 In 1994, for 3,065 nurses, the response rate after two recalls was 62%, or 1,891
participants. This response rate compares favorably with the 51% to 74% response
rate of the studies reviewed that also had members of the research team distribute
questionnaires to the nursing staff on each unit ( Baker, Carlisle, Riley, Tapper, &
Dewey, 1992 ; Beehr, King, & King, 1990 ). The possibility of a selection bias has
nevertheless been discussed in a previous article and is not believed to substantially
affect the results of the study ( Bourbonnais et al., 1998 ).
At T2, a questionnaire was sent to 1,741 of the 1,891 nurses who had participated at
T1. One hundred and thirty nurses were excluded because they were absent from
work during the second period of data collection. The questionnaires of 20 other
respondents could not be used because of missing data. The overall response rate at
T2 was 79% ( n = 1,378), with a range of 77% to 86%. One hospital had a response
rate of 64%. Comparisons of characteristics at T1 were made between respondents
and nonrespondents at T2. These comparisons showed no significant differences in
the prevalence of job strain exposure, psychological distress, or emotional exhaustion
at T1.
In 1994, the nurses who participated in the study were mostly bedside nurses (80%)
and mainly worked full time (58%). Their mean age in 1994 was 39.6 years, and the
mean level of seniority was 15 years. Half of them had a college education, 35% had a
university degree, and 15% had hospital training only. Every work schedule was
represented with 40% of the nurses working during the day, 19% during the evening,
15% at night, and 26% on rotating shifts. Most of them worked on general or
specialized units (57%), whereas the others worked on critical care or emergency
units, including float team. According to human resources representatives and union
members, these proportions among the participants were similar to those found in
their respective hospital.
Psychological Distress
A 29-item self-administered questionnaire, the Psychiatric Symptom Index (PSI), was
used to measure the presence and degree of anxiety, aggressiveness, depressive
symptoms, and cognitive problems during the last week ( Préville, Boyer, Potvin,
Perreault, & Légaré, 1992 ). It is a French version of an American-validated
instrument ( Ilfeld, 1976 ). This French PSI has been validated and used in a
provincial population-based survey: the Québec Health Survey (QHS; Préville et al.,
1992 ). In the present study, the Cronbach coefficient for internal consistency was .93.
A total score of psychological distress with a range of 0 to 100 was calculated from
the responses to the 29 items of the PSI. The PSI score was then dichotomized at the
highest quintile of the distribution of psychological distress in the population of the
QHS ( Santé Québec, 1988 ). Respondents scoring over the fifth quintile were
considered as having a high level of psychological distress symptomatology.
Burnout
A 22-item self-administered questionnaire, the Maslach Burnout Inventory, was used
to measure emotional exhaustion (EE), depersonalization (DP), and personal
accomplishment (PA; Maslach & Jackson, 1986 ). It is a validated French version (
Dion & Tessier, 1994 ) of a validated and frequently used American instrument. In the
present study, the Cronbach coefficients for internal consistency were .89 for EE, .72
for DP, and .74 for PA. A score for each dimension of burnout is obtained on a
continuum of low to high burnout. The cutoff point to determine a high level on each
dimension was established at the upper third (lower third for PA) of the distribution of
the scores at T1. In this article, only the EE dimension was analyzed in detail because
it is considered to be the key dimension of the syndrome. This component also has
been found to have the most robust and consistent relationships with various job
stressors such as work overload, lack of social support, and problems with role (
Schaufeli & Dierendonck, 1993 ).
Job Strain
A self-administered 18-item questionnaire from the Job Content Questionnaire (JCQ),
recommended by Karasek (1985) , was used to measure psychological demands and
job decision latitude. Psychological demands evaluates the quantity of work, the
intellectual requirements, and the time constraints of the job; decision latitude
evaluates opportunities to make decisions, to be creative, and to use and develop one's
abilities at work. The validity of the JCQ has been assessed in national populationbased studies in the United States ( Karasek, 1985 ; Karasek & Theorell, 1990 ). The
French version of the JCQ was validated with a population of 8,263 white-collar
workers from 20 organizations in Quebec City ( Brisson et al., in press ). In our study,
internal consistency based on Cronbach's coefficient alpha is .72 for job decision
latitude and .79 for psychological demands. The exposure to psychological demands
and decision latitude was determined by a threshold fixed at the median of the
distribution of the total score of each of these variables in our study population (high
psychological demands: score >= 11 and low decision latitude <= 70). This allowed
the classification of nurses into four exposure groups with respect to job strain. Nurses
exposed to a combination of high psychological demands and low job decision
latitude (PD + DL) composed the high job strain group; nurses exposed to high
psychological demands but having high decision latitude (PD + DL+) and nurses
exposed to low decision latitude but not exposed to high psychological demands (PD
 DL) were considered to have intermediate exposure; and finally, nurses exposed to
none of these conditions (PD  DL+) composed the nonexposed group.
Because job strain was measured at T1 and T2, cumulative exposure to high job strain
was assessed. Four groups were identified: nurses unexposed at both times, nurses
exposed at T1 but not at T2, nurses unexposed at T1 but exposed at T2, and nurses
exposed at both times.
Social Support at Work
Social support at work was measured by a validated index of eight items from the
JCQ assessing support from supervisors and colleagues ( Karasek, 1985 ), which were
summed to generate a total score. The Cronbach internal consistency coefficient for
the total score in our data was .83. The scores were then dichotomized using the total
sample median to differentiate between high and low social support at work.
Demographic and Work-Related Variables
Participants provided information on their age, seniority, level of training, job title,
hours worked per week, work unit, and shift worked. Measures of Type A behavior,
domestic load, recent stressful life events occurring in the past 12 months, and social
support outside of work were also included in the questionnaire (details of these
measures can be found in Bourbonnais et al., 1998 ).
Data Analysis
For the cross-sectional data, the data were analyzed at T2 independently from T1, and
the aggregated data were compared between T1 and T2. Prevalence ratios were
calculated with their 95% confidence interval for the association among job strain,
psychological distress, and emotional exhaustion. The modifying effect of each
covariate was evaluated by stratification ( Rothman, 1987 ). There is no easy way to
do multiple analysis that is interpretable in terms of prevalence ratio (PR). Therefore,
logistic regression was used to generate adjusted odds ratios (ORs) controlling for
potential confounders ( Hosmer & Lemeshow, 1989 ).
For the evolution of psychological distress between T1 and T2, the data were
analyzed as matched pairs to calculate a cumulative exposure and to control for the
level of psychological distress at T1. A comparison of means was done for each level
of cumulative job strain exposure. A stratified analysis by linear regression was done
on each covariate to evaluate effect modification and confounding ( Kleinbaum,
Kuppen, & Muller, 1988 ). Data analysis was done with SAS/Stat User's Guide ( 1990
). The significance level for all statistical tests was fixed at .05.
Results
The distribution of nurses in the four job strain exposure groups at T2 was 22% in the
nonexposed nurses (PD  DL+), 22% and 29% for the moderately exposed nurses
(PD + DL+ and PD  DL, respectively), and 31% in the most exposed nurses (DP +
DL). For the cumulative exposure, 57% of nurses were not exposed to high job
strain at either times, 12% of participants were not exposed at T1 but were exposed at
T2, 16% were exposed at T1 but not at T2, and finally, 16% were exposed to high job
strain at both times. Social support scores were divided on the median of the
distribution of nurses participating in the study at T1. At T2, the proportions of high
and low social support are similar to the ones reported at T1, around 50%. In 1995,
35% of nurses declared being highly concerned about their job security even though
they had permanent status in the hospital. This is a 50% increase from 1994. The
desire to change job or to stop working was present everyday or once a week in 22%
of the nurses, whereas 24% never thought of this possibility.
At T2, the prevalence of psychological distress was 32% (with a range of 26% to 35%
throughout the six hospitals in the study) compared with 28% in 1994. The prevalence
of burnout (high level of EE and DP and low level of PA) was 11% (with a range of
9% to 15%) compared with 8% at T1. It is noteworthy that the prevalence of the two
mental health indicators in this study is rather stable between T1 and T2. There was
no statistical difference in scores between the two data collection periods.
As shown in Table 1 , at T2, a combination of high psychological demands and low
decision latitude was associated with psychological distress (PR = 2.31). A moderate
exposure to job strain was also associated with psychological distress (PR = 1.71 for
exposure to high psychological demands only and PR = 1.43 for exposure to low
decision latitude only), as was low social support at work (PR = 1.69). Other factors
were associated with psychological distress: high job insecurity, night work, Type A
behavior, low alcohol intake during the last week, low social support outside of work,
stressful life events occurring during the last year, and high asymmetry in domestic
chores. Nurses with a university degree rated low on psychological distress. Most of
the variables associated with psychological distress at T2 were also risk factors at T1
although the strength of the association has decreased at T2. Other factors not
associated with the prevalence of psychological distress at T2 were age, hospital,
work unit, number of hours worked in a week, work status, job title, and seniority in
the hospital or in the work unit.
As shown in Table 2 , at T2, emotional exhaustion was associated with high job strain
(PR = 3.81), with moderate job strain (PR = 2.61 for high psychological demands
only and PR = 1.62 for low decision latitude only), and with low social support at
work (PR = 1.91). Other factors associated with emotional exhaustion were high job
insecurity, having to work 35 hr or more per week, alcohol intake, Type A behavior,
and low social support outside of work. The association between emotional
exhaustion and work unit was also significant, showing a protective effect of working
in pediatrics. As for psychological distress, most factors associated with emotional
exhaustion were also associated at T1. Factors that were not associated with the
prevalence of emotional exhaustion at T2 were age, smoking, hospital, type of
training, job title, schedule, seniority in the hospital or the work unit, domestic load,
and stressful life events.
We evaluated the modifying effect of each covariate, including social support at work,
on the association between job strain and psychological distress and job strain and
emotional exhaustion. Social support did not modify the association. For every
exposure groups, the OR did not vary meaningfully with the level of social support.
No other factors modified the association in this study.
A multivariate logistic regression analysis was performed to adjust simultaneously for
several potential confounders. Table 3 shows adjusted ORs for psychological distress,
emotional exhaustion, and job strain. This association tended to be stronger when
there was a combination of high psychological demands and low job decision latitude.
There was a multiplicative effect of the combination of high psychological demands
and low decision latitude with psychological distress and emotional exhaustion.
However, exposure to one or the other of these factors was also associated with an
elevated level of psychological distress and emotional exhaustion. The association
between job strain, psychological distress, and emotional exhaustion remained
significant even after adjusting for the following potential confounders: social support
at work, tenure in the hospital (for emotional exhaustion only), number of hours
worked in a week, age, Type A behavior, social support outside of work, and stressful
life events in the last 12 months.
Evolution in Psychological Distress Between 1994 and 1995
The next analyses measured the association between psychological distress at T2
among nurses according to cumulative exposure to high job strain, that is, a
combination of high psychological demands and low decision latitude. Table 4 shows
the means of psychological distress at T2 adjusted for psychological distress at T1.
This adjustment is made because psychological distress at T2 is influenced by its
value at T1. Nurses who were not exposed at T1 and were still not exposed at T2 had
the lowest mean of psychological distress, 19.3; those who were exposed at T1 but not
at T2 followed with a mean of 19.8; then, those who were not exposed at T1 but were
exposed at T2 had a mean of 22.3; finally, nurses who were exposed at both times had
the highest mean, 23.7. The mean of psychological distress of nurses exposed at T2
and the mean of those exposed at T1 and T2 were significantly higher than the mean
of nurses never exposed to high job strain. Other factors associated with a statistically
significant difference in means of psychological distress were social support at work,
job insecurity, Type A behavior, alcohol intake during the last week, social support
outside of work, the occurrence of stressful life events during the last year, and
asymmetry in home chores ( Table 5 ).
Next, the association between psychological distress at T2, adjusted for psychological
distress at T1, and the cumulative exposure to job strain was examined to assess the
influence of confounding factors. The adjustment of the means for each of these
factors taken one by one did not change the means; therefore, only the crude measures
are presented in Table 4 . These results support the association between job strain and
psychological distress among nurses. Nonexposed nurses at both times had the lowest
mean of psychological distress scores, whereas nurses exposed at both times had the
highest mean scores. The other nurses had intermediate means that corresponded to
either the withdrawal of the exposure at T2 with some remaining effect or current
exposure only with some meaningful effect.
Discussion
The present results are consistent with our earlier reported findings ( Bourbonnais et
al., 1998 ). The same associations were found between psychological demands,
decision latitude, and a combination of the two with psychological distress and
emotional exhaustion for current exposure (at T1 and T2) and for cumulative
exposure. Social support had a direct effect on these psychological symptoms but did
not modify their association with job strain.
Landsbergis (1988) also found an association among emotional exhaustion, job strain,
and social support among health care workers. Fong (1993) found that job demands,
time pressure, and support from supervisors and colleagues at T1 predicted emotional
exhaustion of nursing educators 2 years later, at T2. They did not measure decision
latitude or job strain. In their study among Finnish nurses, Elovainio and Kivimaki
(1996) found that job demands and control had an independent effect on strain
symptoms but no interaction effect. There was a significant interaction of job
demands and goal clarity, the latter modifying the effect of job demands on
symptoms. Their measure of job control did not include the use of one's abilities in
the job as in Karasek's concept of decision latitude but was rather restricted to the
opportunity to influence quantitative and qualitative aspects of their job. De Jonge et
al.(1996) supported the effect of a combination of high demands and low autonomy in
the occurrence of emotional exhaustion among health care professionals.
Only Parkes et al. (1994) demonstrated a significant interaction among job strain,
social support, and symptomatic symptoms, showing a buffering effect of social
support in a population of health care professionals. Others who found a significant
association of job stress or job strain on emotional exhaustion among nurses or health
professionals did not find a significant interaction with social support ( De Jonge et
al., 1996 ; Parker & Kulik, 1995 ). Landsbergis (1988) did not test the modifying
effect of social support at work in his study among health care professionals.
Most of the studies on job strain showed direct effects of psychological demands,
decision latitude, and social support at work on the prevalence of psychological
symptomatology; most of them supported an effect of the combination of high
demands and low latitude but did not support a modifying effect of social support. As
suggested by Kinicki and McKee (1996) , the inconsistent results on the role of social
support in the stress—strain association may be due to different operationalizations of
social support.
All hospitals in the study had an employee assistance program (EAP), but in some
cases, these programs were recent and not greatly used by the employees.
Furthermore, in the province of Quebec, the EAPs deal mostly with personal
problems not necessarily related to the work activity and are not intended to stimulate
the development of organizational mechanisms to alleviate job stress. The EAPs were
therefore not included as a factor potentially confounding the association measured in
our study.
Because of the cross-sectional design, the causal direction between job strain and
psychological disorders cannot be determined. However, in the absence of a thorough
follow-up, our measure of cumulative exposure over more than 1 year enabled us to
study the development of psychological distress over time according to job strain.
This is an original contribution to the field.
A selection bias may have happened because we could not contact the nurses who
were absent from work during data collection at T1 or at T2. This could have
introduced an underestimation of the prevalence of psychological symptomatology
among the study population, if the nurses were absent because of psychological
disorders. To estimate the effect of this potential bias on the association between job
strain and psychological disorders, we compared nurses who did not respond to the
questionnaire at T2, including those who could not be contacted, with the nurses who
responded at T1 for the main factors of the study: job strain, social support at work,
psychological distress, and emotional exhaustion. There were no significant
differences in the prevalence of these factors at T1 from the participants and the
nonparticipants at T2, thus reducing the possibility of a bias in the associations
measured.
Information bias could be a potential threat to the validity in our study, because
information on exposure or work constraints and health was obtained through selfreports. This bias may have caused overestimated ORs if nurses having psychological
disorders tended to perceive and report their work situation differently and report
more job strain, or because a complaining attitude toward work and health may have
resulted in negative reports of both constraints and mental health problems. A few
authors measured negative affectivity to help interpret their data or control for this
potential bias ( Chen & Spector, 1991 ; Stansfeld et al., 1995 ). They found that
although the associations between self-reported work conditions and psychiatric
disorders were partly explained by negative affectivity, these associations were still
significant after adjusting for negative affectivity ( Chen & Spector, 1991 ; Stansfeld
et al., 1995 ). We did not measure this factor. However, the purpose of the study was
to identify adverse environmental conditions, which are amenable to intervention,
rather than personality traits associated with high vulnerability, which are not readily
changed. In addition, the possible impact of high-strain jobs on presumably stable
personality variables such as negative affectivity has yet to be explored ( Landsbergis
et al., 1992 ). In fact, adjusting for negative affectivity while examining the
association between job strain and psychological disorders may result in
overadjustment because negative affectivity may be influenced by psychological
disorders, job strain, or both.
Another way to control for information bias is to include objective measures of job
strain. We did not have an objective or outside measurement of job constraints. We
had planned to take the work unit as an independent indicator of job demands, but
after consulting with the organization responsible for giving us access to this
information to characterize job demands on each unit and each hospital in the study,
we found that the validity of data for a research purpose was not sufficient. Yet,
authors who made a comparison between self-report exposure and one that was
independently assessed found moderate associations between the two ( Karasek, 1979
; Spector, Dwyer, & Jex, 1988 ). This suggests that self-rated measures of work are at
least partially measuring the same underlying construct as the external measures of
work. Questionnaires have mostly been used to measure perceived work environment,
which has been shown to have a stronger association with health and well-being than
external evaluations of work ( Lindstrom, 1994 ). Thus, it may be the perception of
constraints that affect mental health the most. Indeed, perception of work environment
may be a mediating factor between objective work conditions and psychological
outcomes, which would suggest that it may be the nurses' perceptions and
interpretation of their working conditions rather than these conditions per se that
influence psychological disorders.
One advantage of self-report measures of work constraints in our study was that they
produced individual measures rather than average measures based on occupational
titles, which are often used in studies and which lead to potential exposure
misclassification and information bias because they might limit between-jobs variance
in psychological demands and decision latitude. Furthermore, we had three dependent
variables in our study and all three were in the same direction as a more objective one,
certified sick leave, which was also associated with the symptoms reported (
Bourbonnais, Comeau, Dion, & Vézina, 1997 ).
An information bias may have been introduced through the cumulative exposure
measure of job strain, if there was exposure variation during the period between the
two measures. This would produce a nondifferential information bias and would
signify an underestimation of the true effect of cumulative job strain on psychological
disorders.
Finally, we have to mention that although the job strain model has mostly been tested
among nonspecific work groups, our study was done in a specific and homogeneous
work group: nurses working in acute care hospital centers. In studying nurses, we had
to make some changes from the usual way of analyzing job strain. In fact, we could
not take the cutoff point for the scores of psychological demands and decision latitude
from the median value of the distribution in the general population (9 for demands
and 72 for latitude; Brisson et al., in press ) as is ordinarily done for a dichotomous
variable of job demands and job latitude. If we had done so, too many nurses would
have been in the exposed group for high demands (75%), low latitude (67%), and high
job strain (49%), and there would have been too few nurses in the nonexposed groups
(7% in the reference category of job strain). As the goal of our study was to classify
nurses correctly according to their own workload (internal validity) rather than to
compare nurses with the general population (external validity), we chose a cutoff
point at the median of the distribution among the nurses for each of the two factors:
70 for latitude and 11 for demands. In this way, more nurses were in the nonexposed
category of job strain (17%). The association between high demands combined with
low latitude and psychological distress at T1 with the national cutoff points (72 for
latitude and 9 for demands) was PR = 2.88 compared with PR = 2.44 in our analysis,
thus showing an underestimation in our study caused by the unexposed group being a
mix of exposed and unexposed nurses according to the definition of exposure based
on national medians.
Conclusion
Overall, although the study may have some biases that are hard to eliminate in a
cross-sectional design, it provides more support for the hypothesis of an association
between job strain and psychological disorders, which has obtained controversial
results up until now. However, it does not support the demand—control and social
support hypothesis, although it shows a direct effect of social support at work on
psychological symptomatology. Furthermore, in the absence of a thorough follow-up,
our measure of cumulative exposure over more than 1 year enabled us to study the
development of psychological distress over time according to job strain. This is an
original contribution to the field.
Although we used cumulative exposure to test the model, a more precise measure of
the exposure in time is necessary to study the chronic effect of job strain on mental
health as well as physical health. To reach this goal, one needs longitudinal and
prospective data to study the occurrence and persistence of health problems when
exposure is maintained or retrieved. Interventions in the workplace should consider
both the subjective and the objective environment if psychological health is to be
enhanced.
Work conditions associated with psychological distress and emotional exhaustion are
often modifiable. In answer to an open-ended question, nurses identified
improvements that could be made to ameliorate their work conditions. The
improvement most frequently mentioned concerned job demand, which could be
lessened if the division of work was more explicit between the different members of
the healing team. The second improvement suggested referred to social support at
work, which should be enhanced with more tangible cognitive support from
supervisors and colleagues to facilitate clinical decisions, more recognition and
appraisal from superiors, and the opportunity to discuss tensions at work. Job latitude
was mentioned by fewer nurses, but many indicated their wish to be part of the
decision-making process and to have the possibility to develop their professional
skills.
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1
This study was conducted before the major restructuring and downsizing in the health
care system in the province of Quebec for which a 3-year plan was presented in spring
1995 but the major changes occurred in spring 1996. Therefore, these issues are not
addressed in this article.
This research was founded by the Conseil Québécois de la Recherche Sociale and the
Fonds Pour la Formation de Chercheurs et l'Aide à la Recherche. We wish to thank all
nurses who participated in the study and the people from human resources
management and unions responsible for its realization in each hospital. We
acknowledge the contribution of Guylaine Dion to the planning phase of the study.
We are also thankful to Danny Laverdière, Caroline Migneault, Brigitte Gagnon, and
Dominique Dion for data collection and coding, Pascale Bernard and Myrto Mondor
for data processing, and Angela Colantonio for reviewing the English version of this
article.
Correspondence may be addressed to Renée Bourbonnais, Faculty of Medicine, Laval
University, Ste-Foy, Quebec, Canada, G1K 7P4.
Electronic mail may be sent to renee.bourbonnais@erg.ulaval.ca
Received: February 16, 1998
Revised: May 6, 1998
Accepted: July 28, 1998
Table 1. Crude Prevalence Ratio (PRep) and 95% Confidence Interval (CI) for
Psychological Distress According to Work and Nonwork Conditions at Time 2
Table 2. Crude Prevalence Ratio (PR) and 95% Confidence Interval (CI) for
Emotional Exhaustion (EE) According to Work and Nonwork Conditions at Time 2
Table 3. Crude and Adjusted Odds Ratio (OR) and 95% Confidence Interval (CI)
Between Psychological Distress or Emotional Exhaustion (EE) and Job Strain at Time
2
Table 4. Psychological Distress Mean Scores at Time 2 Adjusted for PSI at Time 1
and 95% Confidence Intervals (CI) According to Cumulative Exposition to Job Strain
Table 5. Psychological Distress Mean Scores at Time 2 Adjusted for PSI at Time 1
and 95% Confidence Intervals (CI) According to Associated Variables at Time 1