Introduction
In the UK, the recent Black report put the prevention of illness and the promotion of well-being and health at the heart of its vision for the working population (Black, Reference Black2008). Prospective evidence for an effect of psychosocial work stress on common mental disorders (CMDs) has increased over the past decade (Stansfeld & Candy, Reference Stansfeld and Candy2006; Siegrist, Reference Siegrist2008), with studies assessing psychosocial work stress, characterized by job strain (Karasek, Reference Karasek1979; Johnson & Hall, Reference Johnson and Hall1988) and effort–reward imbalance (ERI) (Siegrist, Reference Siegrist1996) showing effects on anxiety and mood disorders (de Lange et al. Reference de Lange, Taris, Kompier, Houtman and Bongers2003; Stansfeld & Candy, Reference Stansfeld and Candy2006; Netterstrom et al. Reference Netterstrom, Conrad, Bech, Fink, Olsen, Rugulies and Stansfeld2008; Siegrist, Reference Siegrist2008). Job strain and ERI are postulated to influence CMD via an imbalance between job demands and control (Karasek, Reference Karasek1979; Johnson & Hall, Reference Johnson and Hall1988) and job efforts and rewards (Siegrist, Reference Siegrist1996), respectively. However, while associations have been established between psychosocial work stressors and CMD, other factors such as recent life events (Melchior et al. Reference Melchior, Berkman, Niedhammer, Zins and Goldberg2007), prior psychological ill health (Hammen, Reference Hammen2005; Clark et al. Reference Clark, Rodgers, Caldwell, Power and Stansfeld2007a), childhood adversity (Rodgers, Reference Rodgers1990; Clark et al. Reference Clark, Caldwell, Power and Stansfeld2010), caring responsibilities (Weich et al. Reference Weich, Sloggett and Lewis2001; Pinquart & Sorensen, Reference Pinquart and Sorensen2003), socioeconomic status (Lorant et al. Reference Lorant, Deliege, Eaton, Robert, Philippot and Ansseau2003), domestic abuse (Al-Modallal et al. Reference Al-Modallal, Peden and Anderson2008), housing quality (Weich et al. Reference Weich, Blanchard, Prince, Burton, Erens and Sproston2002; Clark et al. Reference Clark, Stansfeld and Candy2007b), work-to-family conflict (Lennon & Rosenfield, Reference Lennon and Rosenfield1992; Allen et al. Reference Allen, Herst, Bruck and Sutton2000) and social support (Stansfeld et al. Reference Stansfeld, Rael, Head, Shipley and Marmot1997b; Fuhrer et al. Reference Fuhrer, Stansfeld, Chemali and Shipley1999) also show robust associations with CMD, indicating that psychological disorders have a multi-factorial causation (Hammen, Reference Hammen2005).
To date, only a few studies of psychosocial work stress and CMD have included non-work stressors. These studies suggest an independent effect of both work stressors and non-work stressors on depression and psychiatric sickness absence (Phelan et al. Reference Phelan, Schwartz, Bromet, Dew, Parkinson, Schulberg, Dunn, Blane and Curtis1991; Stansfeld et al. Reference Stansfeld, Fuhrer, Head, Ferrie and Shipley1997a, Reference Stansfeld, Bosma, Hemingway and Marmot1998; Weinberg & Creed, Reference Weinberg and Creed2000; Cole et al. Reference Cole, Ibrahim, Shannon, Scott and Eyles2002; Griffin et al. Reference Griffin, Fuhrer, Stansfeld and Marmot2002; Artazcoz et al. Reference Artazcoz, Artieda, Borrell, Cortes, Benach and Garcia2004; Wang, Reference Wang2006; Melchior et al. Reference Melchior, Berkman, Niedhammer, Zins and Goldberg2007) but have poorly conceptualized and weakly measured non-work stressors, with studies tending to focus on only one type of non-work stressor. To better inform interventions for managing stress in the workplace, associations between work stressors and a range of different types of non-work stressors need exploring in general population samples. It is not known if interventions that focus solely on work stressors will be as effective in tackling CMD as interventions addressing both types of stressors.
We conducted analyses of the 2007 Adult Psychiatric Morbidity Survey (APMS) to determine the contribution of stressors in the workplace to psychological ill health compared with stressors from non-work domains in a general population sample. First, we examined the individual associations of CMD with a range of work stressors and non-work stressors (recent life events, caring responsibilities, domestic abuse, financial difficulties, poor housing quality and non-work social support). Interactions with gender were examined as the impact of stressors on CMDs differs for women and men, as do effects for non-work stressors (Kendler et al. Reference Kendler, Thornton and Prescott2001; Stansfeld & Candy, Reference Stansfeld and Candy2006; Oldehinkel & Bouma, Reference Oldehinkel and Bouma2010). Second, we determined the relative contribution of work stressors and non-work stressors to CMD by assessing whether any significant associations between work stressors and CMD were explained by adjustment for the non-work stressors. Finally, we examined whether non-work stressors such as social support (Phelan et al. Reference Phelan, Schwartz, Bromet, Dew, Parkinson, Schulberg, Dunn, Blane and Curtis1991; Stansfeld et al. Reference Stansfeld, Rael, Head, Shipley and Marmot1997b) and life events (Melchior et al. Reference Melchior, Berkman, Niedhammer, Zins and Goldberg2007) could also moderate effects of work stressors on CMD.
Method
Setting and participants
The 2007 APMS is a stratified probability sample survey conducted between October 2006 and December 2007 among adults aged ⩾16 years living in private households in England (McManus et al. Reference McManus, Meltzer, Brugha, Bebbington and Jenkins2009). The response rate was 57% (n=7461); 30% refused and 13% were uncontactable (McManus et al. Reference McManus, Meltzer, Brugha, Bebbington and Jenkins2009). These analyses selected working age participants (males 16–65 years, females 16–60 years, based on retirement age for each gender) who were employees and had provided complete data on all of the work and non-work stressors (N=3383: 1804 males; 1579 females). The sample included those on short-term sickness absence but excluded those on longer-term sickness absence. Employment status was self-reported.
The survey had a multi-stage, stratified random probability sampling design, using the small users Postcode Address File as a sampling frame. Approximately 14 500 addresses were selected. Interviewers visited the addresses and one eligible occupant aged ⩾16 years was randomly selected. Ethical approval for the APMS was awarded by the Royal Free Multi Regional Ethical Committee (Ref: 06/Q0501/71) (McManus et al. Reference McManus, Meltzer, Brugha, Bebbington and Jenkins2009). The survey involved a 90-min computer-assisted personal interview (CAPI), which assessed CMD, current work and non-work stressors and sociodemographic factors using standardized, validated self-report measures.
Measures
Common mental disorder
CMD was measured in the survey using a structured diagnostic interview – the Revised Clinical Interview Schedule, which assesses the prevalence of ICD-10 diagnoses of common depressive and anxiety disorders in the past 7 days (Lewis et al. Reference Lewis, Pelosi, Araya and Dunn1992). CMD was defined as any diagnosis of depressive episode, generalized anxiety disorder, obsessive compulsive disorder, agoraphobia, social phobia, panic or mixed anxiety and depression.
Work stressors
ERI occurs when job efforts are high and rewards are low (Siegrist, Reference Siegrist1996). Over-commitment, an individual's need for approval and esteem at work, can also exacerbate the effects of ERI on psychological health (Siegrist, Reference Siegrist1996). ERI was measured using items from the ERI questionnaire (Siegrist et al. Reference Siegrist, Wege, Pühlhofer and Wahrendorf2009) assessing the work environment in the past year. Effort was measured by three items assessing the demands of the work environment, e.g. having many interruptions and disturbances. Rewards were assessed using eight items covering job security, promotion prospects, respect and esteem. Over-commitment was assessed using six items assessing attitude to work. Reliability for these scales was good; Cronbach's α=0.79 for effort, 0.72 for reward and 0.80 for over-commitment.
The job demand-control model (JDC) (Karasek, Reference Karasek1979) proposes that job strain arises when high job demands are combined with low job control. The job demand-control-support model (JCDS) (Johnson & Hall, Reference Johnson and Hall1988) further accounts for the potential for social support at work to moderate the effect of high job demands on psychological health. JDC and JDCS were measured using questions adapted from the Whitehall II study (Karasek, Reference Karasek1979; North et al. Reference North, Syme, Feeney, Shipley and Marmot1996), assessing the work environment in the past year. Due to time constraints, demands were assessed using the questions measuring effort from the ERI model. Job control was measured using two items assessing the extent to which employees have control over their work. Social support in the workplace was assessed using four items, e.g. were colleagues willing to listen to their work-related problems? Reliability for these scales was good; Cronbach's α=0.73 for control and 0.79 for social support at work. The ERI+over-commitment model and the JDCS questions are listed in full in the Appendix.
For both the ERI and the JDC/JDCS measures scores for each individual measure (effort/demands, rewards, over-commitment, control, workplace social support) were summed and divided into tertiles – high, mid, low. As in previous papers, analyses compare the high tertile for effort/demands and over-commitment with the mid- and low tertiles and the low tertile for rewards, control and social support with the mid- and high tertiles (Stansfeld et al. Reference Stansfeld, Bosma, Hemingway and Marmot1998; de Jonge et al. Reference de Jonge, Bosma, Peter and Siegrist2000), The high and low tertiles for the effort and reward measures were then used to allocate respondents into four categories assessing ERI: high effort/low reward (ERI); high effort/high reward; low effort/low reward; low effort/high reward. The tertiles for demands and control were used to allocate respondents into four categories assessing job strain: high demands/low control (job strain); high demands/high control; low demands/low control; low demands/high control.
Three further work-related stressors were assessed using the list of threatening experiences (LTE) (Brugha et al. Reference Brugha, Bebbington, Tennant and Hurry1985) measure of life events in the past 6 months. These were being made redundant, looking for work for >1 month and experiencing violence at work.
Non-work stressors
Recent life events, caring responsibilities, non-work social support, financial strain and housing quality were assessed using CAPI. Non-work life events in the past 6 months were assessed using the LTE (Brugha et al. Reference Brugha, Bebbington, Tennant and Hurry1985), e.g. separation/divorce and financial difficulties.
Caring responsibilities were assessed using a dichotomous measure (no/yes) of whether the participant undertook caring responsibilities: n=584 reported caring for 0–10 h per week; n=212 reported >10 h per week. Debt was indicated by whether the household had become behind with payments for any of a range of bills and loans in the past year (Jenkins et al. Reference Jenkins, Bhugra, Bebbington, Brugha, Farrell, Coid, Fryers, Weich, Singleton and Meltzer2008).
Non-work social support was assessed using the Interview Measure of Social Relationships (Brugha et al. Reference Brugha, Sturt, MacCarthy, Potter, Wykes and Bebbington1987, Reference Brugha, Morgan, Bebbington, Jenkins, Lewis, Farrell and Meltzer2003), a standardized validated measure. Scores on the items are summed and categorized as good support (score=21), mid-support (score 18–20) and low support (score <18).
Housing quality was assessed by a dichotomous measure based on whether there was mould in the respondent's home over the past year. This variable indicates poor housing quality in the UK as it is a marker of an energy-inefficient home and also indicates fuel-related poverty (Harris et al. Reference Harris, Hall, Meltzer, Jenkins, Oreszczyn and McManus2010).
Domestic violence and abuse was assessed using computer-assisted self-interview to encourage full disclosure. A dichotomous variable contrasting the absence of domestic abuse with any report of domestic abuse was created from reports of whether in the past year a previous or current partner had hit them, slapped/pinned them down, threatened them with a weapon, threatened to kill them or used a weapon on them.
Sociodemographic factors
The analyses use measures of age, gender, tenure (home owned/mortgaged versus rented/other) and marital status (married; single; separated/divorced/widowed/other) (McManus et al. Reference McManus, Meltzer, Brugha, Bebbington and Jenkins2009).
Analysis
The prevalence of each work and non-work stressor for the sample and for those reporting CMD was established. Preliminary logistic regression analyses assessed associations between the individual work and non-work stressor measures and CMD, adjusted for gender, marital status, age and tenure. For job strain and ERI, subsequent adjustments were made for social support at work and over-commitment, respectively, to assess the full work stress models.
A multivariate regression model assessing the adjusted odds for CMD was then run, combining the JDCS work stressors and the non-work stressors. This model was adjusted for all the JDCS work and non-work stressors, which had been significantly associated with CMD in the preliminary regression analyses, as well as age, gender, tenure and marital status. The potential moderators of gender, non-work social support and financial difficulties were examined using multiplicative interaction terms (Zammit et al. Reference Zammit, Lewis, Dalman and Allebeck2010a, Reference Zammit, Wiles and Lewisb). This process was repeated for a multivariable regression model combining the ERI+over-commitment work stressors and the non-work stressors.
Analyses were conducted in SPSS Version 16.0 (SPSS Inc., USA) using the complex samples analysis function taking weighting and survey design into account.
Results
Descriptives for the sample
The mean age was 38 years; 53% were male; 52% were married, 13% cohabiting, 27% single, 5% divorced and 3% widowed/separated; 16% owned their home, 57% were buying with a mortgage, 24% rented and 3% lived in the house for free.
Of the sample, 14.4% had a CMD defined as one or more of the following diagnoses: depressive episode; generalized anxiety disorder; mixed anxiety disorder; social phobia; agoraphobia; panic or obsessive compulsive disorder.
Prevalence of work stressors and associations with CMD
Nearly 12% of the sample reported job strain. Table 1 shows the associations of the JDC and the JDCS models with CMD, adjusted for gender, age, marital status and tenure. After adjustment for social support at work, job strain (high demands/low control) was associated with a three-fold increase in odds for CMD and an active job (high demands/high control) was associated with nearly double the odds. Low and mid-levels of social support at work were also significantly associated with increased odds of CMD.
Odds ratios showing the associations of job strain, effort–reward imbalance and work-related recent life events on common mental disorder adjusted for age, gender, tenure and marital status
CMD, Common mental disorder; JDC, job demand-control; JDCS, job demand-control-support; ERI, effort–reward imbalance.
Nearly 13% of the sample reported ERI. Table 1 also shows the associations of the ERI and the ERI+over-commitment models with CMD adjusted for gender, age, marital status and tenure. After adjustment for over-commitment, ERI (low rewards/high effort) was associated with a three-fold increase in odds for CMD and low reward with low effort was associated with double the odds. High over-commitment was associated with a 3.5-fold increase in odds for CMD.
No significant associations were observed between the work-related life events in the past 6 months – being made redundant, looking for work without success or violence at work – and CMD. No gender interactions were observed between the work stressors and CMD, with the exception of being made redundant in the past 6 months (p=0.047). After stratification there was a significant effect of being made redundant on CMD for females [odds ratio (OR) 4.32, 95% CI 1.39–13.46] but not for males (OR 0.60, 95% CI 0.14–2.65) but these analyses were underpowered, with only 23 males and 15 females reporting redundancy in the past 6 months.
Prevalence of non-work stressors and associations with CMD
Table 2 shows the associations between the individual non-work stressors and CMD. In total, 18% of the sample reported experiencing at least one of the non-work life events in the past 6 months, which was associated with a 1.5-fold increase in odds for CMD. The serious illness/injury/assault of a close relative was associated with a 2.2-fold increase in odds for CMD, separation and divorce with nearly a 2.4-fold increase in odds, a major financial crisis with a 3.9-fold increase in odds and problems with the police with a 6.8-fold increase in odds. Domestic violence, caring responsibilities, low non-work social support, mould in the home and being in debt were also associated with increased odds for CMD (odds range=1.84–3.59).
Odds ratios showing the associations of non-work stressors (recent life events, caring responsibilities, domestic violence, non-work social support, housing quality and financial strain) on common mental disorder adjusted for age, gender, tenure and marital status
CMD, Common mental disorder.
No gender interactions were observed between the non-work stressors and CMD, with the exception of being in trouble with the police (p=0.018): due to low power, only 10 males and five females reported this life event, preventing stratification by gender to further explore this finding.
Multivariable models of work and non-work stressors
JDCS
Table 3 shows the multivariate regression model, giving the adjusted odds for CMD for the JDCS work stressor measures and the non-work stressors, adjusted for age, gender, marital status and tenure. In this fully adjusted model, both work and non-work stressors were significantly associated with CMD. Job strain remained associated with nearly a three-fold increase in odds for CMD and an active job (high demands/high control) with nearly double the odds for CMD. Low and mid-levels of social support at work also remained associated with CMD. A serious illness/injury/assault to a close relative in the past 6 months, domestic violence in the past year, caring responsibilities, low and mid-levels of non-work social support, mould in the home and debt were associated with increased odds for CMD, with odds ranging from 1.59 to 2.79.
Adjusted odds ratios showing associations of job-demand-control-support and non-work stressors on common mental disorder
CMD, Common mental disorder.
a Adjusted odds ratios are derived from a model adjusting for age, gender, tenure, marital status, job strain, social support at work, serious illness/injury/assault to self, serious illness/injury/assault to close relative, separation or divorce, serious problem with a friend or relative, major financial crisis, problem with the police, domestic violence, caring responsibilities, non-work social support, mould in the home and being in debt.
ERI model
Table 4 shows the multivariate regression model, giving the adjusted odds for CMD for the ERI+over-commitment work stressor measures and the non-work stressors, adjusted for age, gender, marital status and tenure. In this fully adjusted model, both work and non-work stressors were significantly associated with CMD. ERI (low rewards/high effort) remained associated with nearly a three-fold increase in odds for CMD and low rewards/low effort with a 1.6-fold increase in odds for CMD. High over-commitment was associated with a 3.4-fold increase in odds for CMD. A serious illness/injury/assault to a close relative in the past 6 months, domestic violence, caring responsibilities, low and mid-levels of non-work social support, mould in the home and debt also remained associated with increased odds for CMD, with odds ranging from 1.59 to 2.50.
Adjusted odds ratios showing associations of effort–reward imbalance+over-commitment and non-work stressors on common mental disorder
CMD, Common mental disorder; ERI, effort–reward imbalance.
a Adjusted odds ratios are derived from a model adjusting for age, gender, tenure, marital status, job strain, over-commitment, serious illness/injury/assault to self, serious illness/injury/assault to close relative, separation or divorce, serious problem with a friend or relative, major financial crisis, problem with the police, domestic violence, caring responsibilities, non-work social support, mould in the home and being in debt.
Moderators of the effect of work stress on CMD
There was no significant interaction between JDC or ERI and non-work social support (p=0.435 and p=0.475). There was also no significant interaction between ERI and over-commitment (p=0.887) or between JDC or ERI and being in debt (p=0.318 and p=0.427).
Discussion
Main findings
In a representative general population sample, we found independent effects of work and non-work stressors on CMD. Job stress, whether conceptualized as job strain or ERI, together with lower levels of social support at work, recent stressful life events, domestic violence, caring responsibilities, lower levels of non-work social support, debt and poor housing quality were all independently associated with CMD. Effects of work stressors on CMD were not explained by co-existing non-work stressors. There were no gender differences in the associations observed between the stressors and CMD. Non-work social support and debt did not moderate the effect of work stressors on CMD.
Strengths and limitations
Due to the cross-sectional nature of this study, we are unable to assess causality between the work and non-work stressors and CMD. The analyses may overestimate the associations and need replicating with prospective data. Further limitations include: the reliance on self-reports of stressors and CMD; lack of examination of differential diagnoses of depression and anxiety because of the high prevalence of anxiety and/or co-morbid anxiety disorders; the possibility that poor psychological health may result in negative ratings of job characteristics (de Lange et al. Reference de Lange, Taris, Kompier, Houtman and Bongers2003); a lack of assessment of personal vulnerability for psychological disorders (Weinberg & Creed, Reference Weinberg and Creed2000); the use of the ERI model effort items to assess demands for the JDC model, which weakens the JDC model assessment; underpowered analyses for individual recent life events; the possibility that the non-work social support measure may reflect social support provided by work colleagues; lack of information about the number of roles within and outside the household; a lack of objective assessment of work characteristics and psychological health. Our sample excludes people with long-term sickness absence, which may influence the strength of associations observed. Our healthy worker sample may be more resilient than the general population.
This study is larger than the previous UK study, which sampled 64 healthcare workers (Weinberg & Creed, Reference Weinberg and Creed2000). Other strengths include: the generalizability of the findings from this representative sample, encompassing a broad range of occupations; the assessment of an extensive range of work and non-work stressors; and measures of non-work stressors, which are not limited to life events.
Work stressors
Job strain and ERI were strongly associated with CMD even after adjustment for non-work stressors, confirming previous prospective studies (Stansfeld & Candy, Reference Stansfeld and Candy2006; Siegrist, Reference Siegrist2008). Given the cross-sectional data, our findings may overestimate the strength of the associations. However, high job demands coupled with high job control and high efforts coupled with high demands also significantly increased the odds for CMD. High control and high rewards were not protective for psychological health, as would be predicted (Karasek, Reference Karasek1979; Siegrist, Reference Siegrist1996). Previous findings could be accounted for by sampling issues, as most studies use occupational samples. However, our findings may reflect that demands and efforts are more damaging for psychological health than for physical health, irrespective of levels of control and effort. In addition, jobs may have become more demanding in recent years, leading to less of a protective effect from control and rewards. Furthermore, the meaning of control may have changed in recent years as technological advances have eroded and altered the boundaries between work and home. Further research examining the moderating effect of control and rewards on the effect of high job demands/efforts on CMD in population samples is required before firmer conclusions can be drawn.
The effect sizes for the work stressors were little attenuated after adjustment for a wide range of non-work stressors, confirming their independent effect on CMD. One exception, where the attenuation was slightly larger, was for those with low reward/low effort jobs. Non-work stressors may play a slightly greater role in the aetiology of CMD for those with low reward/low effort jobs. This could reflect differences in resources or skills to cope with exposure to stressors and potential selection into low reward/low effort jobs for individuals with social disadvantage or previous CMD (Stansfeld et al. Reference Stansfeld, Clark, Caldwell, Rodgers and Power2008).
Our study confirms previous findings that high levels of work social support are protective of psychological health (Stansfeld et al. Reference Stansfeld, Fuhrer, Head, Ferrie and Shipley1997a; Stansfeld & Candy, Reference Stansfeld and Candy2006). The current study found no association between the work-related life events of being made redundant, looking for work or violence at work and CMD, which may reflect the lack of power for these analyses, as we would expect these events to be associated with CMD (Montgomery et al. Reference Montgomery, Cook, Bartley and Wadsworth1999). Our analyses examined individuals who experienced redundancy or unemployment but who found employment again quickly, which is likely to have had a counteracting positive effect on mental health. These associations are likely to differ in a sample including individuals who did not find employment again so quickly. Over-commitment, a measure of excessive striving, showed the strongest association with CMD in the current study and is associated with alterations in the hypothalamic-pituitary-adrenal axis system (Wirtz et al. Reference Wirtz, Siegrist, Schuhmacher, Hoefels, Maier and Zobel2010) and stress responses in the sympathetic nervous system (Wirtz et al. Reference Wirtz, Siegrist, Emini and Ehlert2008). Over-commitment may capture elements of over-investment at work or work–life imbalance. However, over-commitment is also a measure of personality that may reflect low self-esteem; over-commitment could be influencing CMD independently of work characteristics. Over-commitment may prove to be an important aspect to be targeted in occupational interventions for psychological health and should be a focus of future research.
Non-work stressors
This study examines a broad array of non-work stressors, finding independent associations of domestic violence, caring responsibilities, mould in the home and being in debt with CMD, supporting previous findings (Weich et al. Reference Weich, Blanchard, Prince, Burton, Erens and Sproston2002; Lorant et al. Reference Lorant, Deliege, Eaton, Robert, Philippot and Ansseau2003; Clark et al. Reference Clark, Stansfeld and Candy2007b; Al-Modallal et al. Reference Al-Modallal, Peden and Anderson2008). While the individual measures of recent life events were significantly associated with CMD, these associations were mediated by the other measures of work and non-work stressors. After adjustment, there remained only a significant association for serious illness/injury/assault of a close relative. In terms of implications for models of stress in the workplace, an employee with one or more of these stressors is at increased risk for poor psychological health, which could influence sickness absence.
Overall, the current survey found a lower prevalence and subsequently weaker associations between the life events and CMD than the previous APMS 2000 survey (Jordanova et al. Reference Jordanova, Stewart, Goldberg, Bebbington, Brugha, Singleton, Lindesay, Jenkins, Prince and Meltzer2007). While some of the associations between the life events with CMD were similar for the two surveys, e.g. relationship breakdown, associations for most life events were weaker and often non-significant in the APMS 2007 compared with the APMS 2000, e.g. death of a partner or close relative and problems with friends/relatives. The studies share a similar methodology and it is unclear why the findings differ over the 7-year period. The years preceding 2007 may have been beneficial for mental health in the UK but the difference could represent under-reporting of life events in the current survey. Whether similar differences in the prevalence of life events are observed over this period in other panel studies should be examined. The low prevalence for events such as financial crisis, problems with the police and separation/divorce raise the possibility of type II errors. This seems likely given that the effect sizes for these life events in the multivariate models are similar to those for other life events that reach statistical significance.
Independent effects
Our study confirms previous findings of independent effects of work and non-work stressors on CMD (Phelan et al. Reference Phelan, Schwartz, Bromet, Dew, Parkinson, Schulberg, Dunn, Blane and Curtis1991; Griffin et al. Reference Griffin, Fuhrer, Stansfeld and Marmot2002), albeit using a broader range and multiple measures of work and non-work stressors. Non-work stressors do not appear to make a person more susceptible to work-related stressors. Weinberg & Creed (Reference Weinberg and Creed2000) found independent effects of work and non-work stressors on CMD in a small UK healthcare sample, which we replicate in a representative population sample. They found that lack of management support and conflict of work role were independently associated with CMD, while using theoretically based measures, we found effects for job strain and ERI. Taken together, the evidence supports the suggestion that models of stress in the workplace need to incorporate stress outside of the workplace, together with social support (Phelan et al. Reference Phelan, Schwartz, Bromet, Dew, Parkinson, Schulberg, Dunn, Blane and Curtis1991). Moreover, the findings suggest that it is beneficial for employers to tackle workplace stress even if the employee's home life is stressful. The independent effects of work and non-work stressors imply that, potentially, gains can be made from improving the work environment alone.
Gender
Our study confirms those that find no gender differences in the effects of psychosocial work stress on psychological health (Netterstrom et al. Reference Netterstrom, Conrad, Bech, Fink, Olsen, Rugulies and Stansfeld2008) The contrast with studies that suggest gender differences (Artazcoz et al. Reference Artazcoz, Artieda, Borrell, Cortes, Benach and Garcia2004; Chandola et al. Reference Chandola, Martikainen, Bartley, Lahelma, Marmot, Michikazu, Nasermoaddeli and Kagamimori2004) may reflect the occupational homogeneity of those studies compared to the current study. The independent contribution of work and non-work stressors to CMD is compatible with other studies that have concluded that gender differences in rates of CMD are not explained by the number or type of social roles occupied by men and women (Weich et al. Reference Weich, Sloggett and Lewis1998, Reference Weich, Sloggett and Lewis2001). Our findings suggest that it may not be multiple roles that are important for CMD, but the strain experienced within each domain per se.
Moderators of work stress effects on psychological health
We found no support for hypothesized effects of non-work social support, debt and over-commitment as moderators of effects of work stressors on CMD. Other studies have also failed to demonstrate interactions between life events or family stressors or non-work social support and work stressors (Griffin et al. Reference Griffin, Fuhrer, Stansfeld and Marmot2002; Wang, Reference Wang2006; Melchior et al. Reference Melchior, Berkman, Niedhammer, Zins and Goldberg2007). Our findings, taken together with the independent effect of non-work and work stressors on CMD, are supportive of the additive burden model (Dohrenwend & Dohrenwend, Reference Dohrenwend, Dohrenwend, Dohrenwend and Dohrenwend1981), which suggests that each stressor contributes uniquely and independently to CMD.
Conclusions
In terms of the prevention of illness, interventions for managing stress in the workplace have been focused on changing job conditions, teaching people skills to help them cope with job conditions and treating those experiencing high levels of distress (Briner, Reference Briner1997). However, evidence for the effectiveness of interventions to improve workers' health and reduce sickness absence is limited (BOHRF, 2005; Nieuwenhuijsen et al. Reference Nieuwenhuijsen, Bultmann, Neumeyer-Gromen, Verhoeven, Verbeek and Feltz-Cornelis2008). It has also been suggested that the early detection of psychological disorders is important (Weinberg & Creed, Reference Weinberg and Creed2000) and we reiterate the suggestion that existing models of work stress be developed to incorporate non-work stressors. Interventions incorporating non-work stressors may be successful, as non-work stressors can trigger sickness absence. This is of vital importance given, in recent years, the increasing likelihood because of an increase in dual-career couples and working mothers, that employees have substantial household responsibilities as well as work responsibilities (Allen et al. Reference Allen, Herst, Bruck and Sutton2000). It would also be useful for future research to examine which factors predict sickness absence for those with CMD. The development of schemes that incorporate non-work stressors and an assessment of their effectiveness for the prevention of psychological ill health remains the next challenge. However, the findings of this study also suggest that schemes that tackle workplace stress alone may also be effective in improving employee psychological health.
Acknowledgements
The Adult Psychiatric Morbidity Survey 2007 was commissioned by The NHS Information Centre for Health and Social Care with funding from the Department of Health. This secondary analysis was funded by a grant from the Health and Safety Executive and the Department for Work & Pensions. Ethical approval for APMS 2007 was obtained from the Royal Free Hospital and Medical School Research Ethics Committee (reference number 06/Q0501/71).
Declaration of Interest
S. M. and J. H. are employed by the National Centre for Social Research, the primary contractor for APMS 2007.
Appendix
ERI+over-commitment model
Job effort
I have constant time pressures due to heavy workload.
I have many interruptions and disturbances in my job.
Over the past few years, my job has become more and more demanding.
Job rewards
I receive the respect I deserve from my line manager.
Considering all my efforts and achievements, I receive the respect and prestige I deserve from my colleagues.
Considering all my efforts and achievements, I receive the respect and prestige I deserve from my clients.
Considering all my efforts and achievements, I receive the respect and prestige I deserve from my customers.
I have experienced or expect to experience an undesirable change in my work situation.
My job security is poor.
My job promotion prospects are poor.
Considering all my efforts and achievements, my work prospects are adequate.
Over-commitment
I get easily overwhelmed by time pressures at work.
As soon as I get up in the morning I start thinking about work problems.
When I get home I can easily relax and switch off work.
People too close to me say I sacrifice too much for my job.
Work rarely lets me go, it is still on my mind when I go to bed.
If I postpone something that I was supposed to do today I'll have trouble sleeping at night.
Job demand control social support model
Job control
Do you have a choice in deciding how you go about your work?
Do you have a choice in deciding what you do at work?
Job demands
The same eight items listed under Job effort for the ERI+over-commitment model.
Social support in the workplace
Do you get help and support from your colleagues?
Are your colleagues willing to listen to your work-related problems?
Do you get help and support from your line manager?
Is your line manager willing to listen to your work-related problems?
Questions answered using a 4-point Likert scale (1=strongly agree; 2=agree; 3=disagree; 4=strongly disagree; or 1=often; 2=sometimes; 3=seldom; 4=never/almost never).
Open access
