How does employment influence health outcomes? A systematic review of the intellectual disability literature

1.1 Bidirectional relationship between health and employment

As mentioned, employment is generally considered to have a positive influence on health and well-being. Work provides people structure during their day, regular activity, meaningful life goals, opportunities to increase skills, social status, and social connections (Dodu, 2005; Goodman, 2015). Research in the general population has shown a positive relationship between employment and health status (Marwaha & Johnson, 2004). Health has been found to be a predictor of employment (Achterberg, Wind, de Boer, & Frings-Dresen, 2009), as well as an outcome of employment.

There has been less research including people with disabilities that explores the relationship between employment and health, but the research that has been done indicates a similar relationship as in the general population. A review by the National Center on Leadership for the Employment and Economic Advancement of People with Disabilities (LEAD) concluded that employment has a protective impact on health and could lower public expenditures on health across disability populations (Goodman, 2015). Okoro, Strine, McGuire, Balluz, and Mokdad (2007) found that employed people with disabilities had better mental health outcomes than unemployed people with disabilities, even after adjusting for education, marital status, health risk behaviors, body mass index, health care coverage, and self-rated general health. For people with mental health conditions, employment has been associated with reductions in outpatient psychiatric treatment, improved self-esteem, increased social functioning, and improved quality of life (Bouwmans, de Sonneville, Mulder, & Hakkaart-van Roijen, 2015; Luciano, Bond, & Drake, 2014; Marwaha & Johnson, 2004; Weston, 2002). Issues related to job fit may also play a role, Milner, Krnjacki, Butterworth, Kavanagh, and LaMontagne (2015) found that workers with disabilities experienced poorer mental health outcomes when they were working jobs with lower psychosocial quality. Psychosocial job quality consisted of worker’s rating on four job factors: job demands and complexity, job control, perceived job security, and fair compensation. Optimal jobs are defined as jobs where all four factors are rated adaptively by the person. This suggests that the impact of employment on health may be mediated by the fit between a worker and the job.

For people with intellectual disability, employment supports for the past decade have focused on shifting toward integrated versus sheltered employment. Integrated employment occurs in settings where the majority of employees do not have a disability. This shift occurred in part because of the increased psychosocial job quality inherent in integrated employment (see Migliore, Mank, Grossi, and Rogan (2007) for a detailed discussion of integrated vs. sheltered employment). However, limited work has specifically explored the relationship between health and employment in people with intellectual disability, perhaps because issues related to promoting access to integrated employment opportunities have remained so salient.

Longitudinal research is needed in populations of people with and without disabilities to explore the relationship between health and employment over time in people with disabilities, as the nature of many current studies do not allow researchers to explore the directionality of the relationship. That is, does employment improve health, or are more healthy people employed? One review of prospective, longitudinal studies in the general population explored these issues. van der Noordt et al. (2014) found that there was strong evidence that employment positively affected mental health (depression, psychosocial distress, and decline in mental health) in the general population. However, given the potential bi-directional nature of the relationship between employment and health, the authors urged caution in interpreting the direction of the relationship stating “this means that the positive health effects of employment can be affected by the fact that healthier people are more likely to get and stay in employment (p. 735).” The authors also concluded that more work was needed to establish a link between employment and physical health or mortality. Several studies in the review examined general health, however the results from these studies were mixed, and influenced by measurement and definitional factors.

1.2 Contextual factors that impact employment

In the disability literature, personal and contextual factors have been considered relative to employment status. For example, in the general disability literature, self-esteem has been identified as a barrier to employment (Hall & Parker, 2010). In people with intellectual disability, higher motivation has been found to predict job attainment (Hensel, Kroese, & Rose, 2007). In young adults with Down syndrome, health-related issues, such as limited mobility and poorer mental health had negative effects on employment outcomes. Carter, Austin, and Trainor (2012) examined the National Longitudinal Transition Study-2 (NLTS-2) database and found that previous work experience, gender, lower self-care support needs, more social skills, more household responsibilities, and parent and teacher expectations of employment were associated with employment outcomes across disability populations. Other personal factors that researchers have suggested may be related to employment opportunities include younger age, higher levels of adaptive behavior, and absence of emotional and behavioral support needs (Siperstein, Heyman, & Stokes, 2014).

Several studies have established a link between personal self-determination and employment. Self-determination is defined as acting as a causal agent over one’s life, and is manifested by a person setting goals, believing they can affect the outcome of the goals, and directing action to achieve those goals (Shogren et al., 2015). Early research found that people who worked in community settings were more self-determined (Wehmeyer & Bolding, 2001). More recent research has established that self-determination predicts outcomes, including employment (Shogren, Forber-Pratt, Nittrouer, & Aragon, 2013; Shogren, Wehmeyer, Palmer, Rifenbark, & Little, 2015). Additionally, researchers have demonstrated a link between components of self-determination and employment. Shogren and Shaw (2016) found autonomy predicted employment and Santilli, Nota, Ginevra, and Soresi (2014) found that the relationship between life satisfaction and career adaptability was mediated by hope. In this study, career adaptability referred to problem solving and coping strategies that support adaptation to the changing demands of the workplace; while hope referred to a sense of being willing and able to accomplish goals. Similarly, Shogren, Lopez, Wehmeyer, Little, and Pressgrove (2006) found that hope and optimism predicated life satisfaction in youth with cognitive disabilities.

1.3 Contextual factors that impact health and quality of life

Research with people with intellectual disability, generally, tends to either focus on health outcomes or quality of life as an outcome, rather than both. As such, in this review, we will consider the constructs separately while acknowledging that there is a strong relationship between health and quality of life (Wilson & Cleary, 1995). Many similar factors to those described in the section on employment are also associated with health or quality of life. For example, self-determination has been found to be related to quality-of-life outcomes (Lachapelle et al., 2005; Nota, Ferrari, Soresi, & Wehmeyer, 2007), suggesting self-determination may play an influencing role in the relationship between employment and quality of life.

Other personal characteristics, such as health status, adaptive behavior, and challenging behavior are also related to quality of life in people with intellectual disability (Schalock, 2004). Character strengths, involvement in community activities, and religious faith have also predicted well-being in youth with intellectual disability (Biggs & Carter, 2016). In addition, environmental variables, such as perceived social support, residential setting, household activities, earnings, integrated activities, and some caregiver characteristics predict quality of life (Schalock, 2004). In adults with autism, higher levels of perceived support and lower number of unmet formal support needs were associated with higher levels of quality of life (Renty & Roeyers, 2006). This highlights the complex relationship between these constructs.

Studies have consistently shown that people with intellectual disability have poorer health outcomes than people without a disability. However, little research has investigated the predictors of health for people with intellectual disability, and integrated more systematic examination of the relationship between physical health, mental health, and quality of life outcomes generally, or in the context of employment. One review of the literature found that for people with intellectual disability, severity of disability, male gender, and presence of specific genetic disorder have been associated with poorer health (Bittles et al., 2002). Additionally, lower socioeconomic status (SES), social participation, and smaller social networks were related to poorer health. Other research has shown that SES was a stronger predictor of self-rated health than employment status and social participation (Emerson & Hatton, 2007a). SES from childhood can continue to have effects on health through adulthood (Emerson, 2014; Emerson & Hatton, 2007b).

The current research seeks to clarify what is known in the literature about the relationship between employment, health, mental health, and quality of life to provide guidance for future research and practice to expand this body of research. The research questions that guided our review were:

What are the characteristics of studies that focus on employment, health, and quality of life in the intellectual disability field?

2.1 Search strategy

To identify articles for our systematic review, searches of Medline, PsycINFO, CINAHL, and ERIC databases were conducted. To capture the totality of research related to employment, health and quality of life, we did not specify a specific date of publication range. Our search terms were employment AND (health OR life satisfaction OR quality of life) AND (intellectual disability OR mental retardation).

Our initial search resulted in 429 articles. We used a systematic process to identify articles that met our inclusion criteria. In the first step, the lead author reviewed titles and abstracts of articles in the initial search and removed articles that were clearly out of the scope of the review (e.g. studies of caregiver health and predictors of employment). This process removed 358 articles (including 57 duplicates). The lead author then reviewed the remaining 62 articles to determine whether or not the article met the inclusion criteria. To be included in our review, each article had to: (a) include young adult or adult participants with intellectual disability; (b) report the systematic collection of data on health and/or quality of life; (c) either compare groups where one group was employed and one was not OR prospectively follow participants before and after employment; (d) be peer reviewed; and (d) be in English. Thirteen articles were identified that met these criteria. One additional article was added from a reference review of previous studies on employment, bringing the total number of articles to 14.

2.2 Coding procedure

The included articles were coded on three criteria: (1) health construct measured (i.e. health, quality of life, or closely-related construct); (2) relationship between health construct and employment (i.e. positive, negative, or neutral); and (3) design (i.e. prospective or retrospective). If an article reported some positive and some negative results, it was coded as neutral. An article was coded as prospective if a health construct was measured before and after employment. If the study was a secondary analysis looking at relationships between a health construct and employment, it was coded as retrospective.

The first and third authors jointly coded all of the articles to ensure reliability in coding. Agreement or disagreement was scored for each criteria listed previously. Percent agreement was calculated for each criterion by summing the number of agreements and dividing by the total number of articles. When there was disagreement, the authors discussed the article in question and came to a consensus on the coding. The authors ended with 86% average agreement across the criterion.

3.1 Characteristics of the studies

Seven of the thirteen studies investigating health outcomes of employment were conducted in the last ten years. Of the six conducted more than ten years ago, four focused on quality of life (Eggleton, Robertson, Ryan, & Kober, 1999; Kober & Eggleton, 2005; Salkever, 2000; Sinnott-Oswald, Gliner, & Spencer, 1991), one focused on mental health (Petrovski, 1997) and one focused on physical health (Inge, Banks, Wehman, Hill, & Shafer, 1988). The number of participants with intellectual disability in each article ranged from 4 to 3,856, with a mean of 493 and a median of 164. Ages of participants ranged from 10 to 90. The mean age of the articles that reported an age distribution was 28.59. Seven of the articles studied populations outside of the United States. Countries included in the review were Spain, Wales, England, Australia, Ireland, and the United States.

Table 1 lists the design features of each study in the review. Twelve studies measured health constructs retrospectively. Five of the retrospective studies compared health or quality of life outcomes related to daytime status (generally defined as competitive employment, sheltered employment, or day program) of adults with intellectual disability (Beyer et al., 2010; Blick et al., 2016; Foley et al., 2013; Foley et al., 2014;, Salkever et al., 2000). Two studies compared quality of life outcomes of people in supported versus sheltered employment (Kober et al., 2005; Verdugo et al., 2006). Additionally, two studies compared health outcomes based on employment status (paid employment versus unemployed; McGlinchey et al., 2013; Emerson et al., 2008). The remaining two studies investigated health outcomes of employed adults with intellectual disability with no comparison group (Emerson et al., 2014; Petrovski et al., 1997).

Table 1 details the tools that were used to measure health and quality of life. No study measured both health and quality of life. The most common measure of health was a survey question on self-rated health. For example, Emerson and colleagues (2014) asked one survey question “In general, would you say your health is ...  (1) excellent, (2) every good, (3) good, (4) fair, (5) poor’.” Responses for this question were used as the outcome variable in the retrospective analysis. One study used biometric measures of health, including weight, resting pulse rate, blood pressure, hand strength, and body fat content to compare the control (sheltered workshop) and experimental (competitive employment) groups (Inge et al., 1988). A research team member trained in administering biometric assessments measured participants at the research center every three months during the study.

Other researchers used a variety of self-report questionnaires to measure quality of life. The most common measure, the Quality of Life Questionnaire, was used in three studies (Eggleton et al., 1999; Kober & Eggleton, 2005; Verdugo, Jordan de Urries, Jenaro, Caballo, & Crespo, 2006). Additionally, Sinnott-Oswald et al. (1991) used a survey that was based on the Quality of Life Questionnaire. Beyer et al. (2010) used the intellectual disability version of the Comprehensive Quality of Life Scale (Cummins, 1997). The remaining two studies used questionnaire items. Salkever (2000) used three survey questions to measure satisfaction with life in general, spare time, and productivity. The items were used to compare groups based on employment status (Idle, house work only, volunteer, or work). Blick, Litz, Thornhill, and Goreczny (2016) used an 85-item interview that evaluated inclusion; satisfaction; dignity, rights, and respect; fear; choice and control; and family satisfaction. The survey results were compared across groups in different daytime activities (integrated employment, sheltered employment, and day program).

3.3 Overall health and quality of life outcomes

Overall, studies investigating the health effects of employment yielded mixed results. Studies that used self-rated health found that employment was related to better health (Emerson & Hatton, 2008; Emerson et al., 2014; McGlinchey, McCallion, Burke, Carroll, & McCarron, 2013). However, Inge et al. (1988), who measured physical health, found that weight loss, but not pulse, blood pressure, body fat content, or hand strength was impacted by employment. Foley (2013) found that young adults in integrated employment had more visits to the doctor and hospital than those in sheltered employment. It was not clear from this survey, however, if the increased doctor visits indicated poorer health. Related to mental health, Petrrovski (1997) found that workers with intellectual disability who were more satisfied with their job also reported being lonelier. McGlinchey et al. (2013) found that people in paid employment were less likely to have a diagnosis of depression.

More conclusive results were found in studies measuring employment and quality of life. Nine of the 13 articles reported positive health or quality of life outcomes related to employment (see Table 1). Six of these studies compared adults with intellectual disability in supported employment versus sheltered work or attendance in a day program, and generally found that adults in supported employment scored higher on measures of quality of life (Beyer, Brown, Akandi, & Rapley, 2010; Blick et al., 2016; Eggleton et al., 1999; Kober & Eggleton, 2005; Salkever, 2000; Sinnott-Oswald et al., 1991). One article found no difference in quality of life between workers with intellectual disability in supported versus sheltered employment in a Spanish context (Verdugo, 2006). However, this article did find higher ratings of quality of life in workers employed in jobs with a higher degree of “typicalness” (i.e. the degree to which a job resembled the same work as non-disabled coworkers).

4.1 Health outcomes of employment

This literature review suggests that we know little about the health outcomes related to participation in employment for people with intellectual disability. The majority of research occurred in the last ten years, which indicates a larger - but not sufficient - focus on research investigating employment – and health outcomes in particular. The focus on health could be a result of the ICF’s focus on health and participation (Dean, Fisher, Shogren, & Wehmeyer, 2016). Additionally, there has been a major push from stakeholders (policy makers, self-advocates, family members, and professionals) in the last ten years to move employment supports from sheltered employment (i.e. sheltered workshops) to integrated employment (e.g. Employment First initiatives, changes to Medicaid rules regarding employment supports). These initiatives have begun to create momentum for change, but have not yet influenced the overall employment rates for adults with intellectual disability. Therefore, the main research focus right now is on developing and validating models of employment supports to increase integrated employment (Nord et al., 2015). As more people are employed, the field will be able to shift attention to measuring health outcomes, in addition to integrated employment status. However, given research in the general population pointing to a complex, likely reciprocal, relationship between employment and health outcomes additional research, building on the findings of this review is needed to better understand the long-term relationships between employment, health, and quality of life to inform intervention research aimed at improving health for people with intellectual disability through participation in employment.

The five studies that focused on health in this review were not conclusive, although issues related to measurement and time of follow up need to be addressed in future research. McGlinchey et al. (2013) compared self-rated health based on employment status (paid, unpaid, and unemployed) of people with intellectual disability living in Ireland. They found that people in paid employment had higher self-rated health than people in sheltered or unpaid employment, and those in all three employment categories had higher self-rated health than those who were unemployed. Additionally, workers (in paid, sheltered, and unpaid employment) reported higher quality of life, participated more in social activities, and lower levels of depression. Petroviski et al. (1997) studied a small sample of workers with intellectual disability and found that workers with more job satisfaction were less lonely and experienced less stigma at work. This evidence demonstrates the importance of creating contexts where employment is supported. For example, research has found that a good fit between a job and an employee’s interest leads to increased job retention, wages, and hours worked (Pierce, McDermott, & Butkus, 2003). Additionally, more supportive employers and coworkers can enhance the perceived quality of work environment for workers with intellectual disability (Flores, Jenaro, Begoña Orgaz, & Victoria Martín, 2011). Considering the bi-directional influence of health on employment, Foley et al. (2013) healthier workers had a greater likelihood of community employment. This suggests the importance of supporting health to lead to employment as well as recognizing that employment may have a positive impact on health in people with intellectual disability.

Inge et al. (1988) was the only study to use biometric measures of health. The researchers followed workers with intellectual disability and a matched sample of workers in a sheltered workshop for one year starting with job attainment. The only biometric measure to show a difference was weight. Workers in competitive employment showed a significant amount of weight loss compared to workers in the sheltered workshop. This finding indicates that more work is needed to understand biometric measurement related to health. For example, we do not know what changes in biometric measures are reasonable to expect from employment. The vast amount of literature studying health in the general population is not specific about changes in individual health markers (van der Noordt et al., 2014; Waddell & Burton, 2006). Additionally, using biometric measures in employment research can be difficult. Employment specialists are generally not trained to administer biometric measures. Additionally, the process can become unnecessarily cumbersome to the participant if they need to travel to a clinic for measurement. However, with new technologies (e.g. fitbit), obtaining health information for research purposes is becoming more feasible. More work is needed to explore measurement procedures that are psychometrically sound and do not create undue burden on participants.

Two studies done by Emerson and colleagues had somewhat different results related to employment and require further discussion. Emerson and colleagues (2014) found that more social and civic participation, including employment, was related to better self-reported health. In their previous study, Emerson et al. (2008) also found employment to be an indicator of health, but employment was defined as a part of socioeconomic disadvantage, along with overall neighborhood deprivation, and hardship. The authors in the 2008 study were considering employment in terms of financial outcomes rather than participation. These studies, by the same lead author, highlight a dual role that employment can play regarding health. In one case, employment can influence health through more enhancing economic self-sufficiency. In the other, participation through meaningful activities is the indicator of health. In both studies, however, employment showed a positive influence on health. Future research should include measures of participation as well as economic self-sufficiency to better understand the multiple benefits of employment, and their interactions.

4.2 Quality of life outcomes of employment

The evidence from this review generally points to a positive relationship between employment and quality of life. Four of the seven studies compared the self-rated quality of life by daytime activity or type of employment. For example, Beyer (2010), Blick (2016, and Salkever (2000) all compared community employment (including supported employment), sheltered workshop, and day program. All of these articles found that adults with intellectual disability who worked had higher quality of life than those attending day programs. However, there were mixed results related to work setting. Beyer (2010) found no difference on quality of life for people working in community versus sheltered employment. However, two studies that compared groups of workers in integrated and sheltered work and found that workers in integrated settings reported higher levels of quality of life (Kober & Eggleton, 2005; Sinnott-Oswald et al., 1991). It’s possible that Verdugo and colleague’s (2006) finding related to the “typicalness” of the job may shed light on these conflicting results. Further investigation related to not just the location of the employment but also the fit of the job to the person and the degree to which the job is similar to other workers may be useful. Blick (2016) found that workers in community settings had higher levels of financial autonomy, higher sense of community integration, and more choice and control of work responsibilities than people in sheltered employment. This study also found no difference in individuals’ satisfaction of daytime activity. Salkever (2000) found that individuals with intellectual disability who worked, attended school, or volunteered had higher life satisfaction than individuals who were idle during the day or only performed household work. These findings are likely influenced by the fact that so few of adults with intellectual disability work in integrated settings, limiting research that can be done. Additionally, those that do work in integrated settings typically do not work full time. The average number of hours worked in integrated settings by adults with intellectual disability is 25 (Butterworth et al., 2011). This means that those who work in competitive employment likely also spend a significant part of their week in traditional day program settings or at home. This could confound the results since it is in not clear in these studies the amount of time people are spending in integrated employment. A useful future direction of research would be to use number of hours worked in integrated settings as a predictor of quality of life. It is possible that the more time spent in integrated settings (and, therefore the less time spend in sheltered settings) could increase quality of life.

Another possible reason for the difference in findings based on work setting is that each of these studies used a different measure of quality of life. Blick et al. (2016) used a measure developed for a state-wide survey and measured community participation, satisfaction, dignity, rights, respect, fear, choice and control, and family satisfaction as elements of quality of life. Salkever (2000) used data from the National Consumer Survey, which measured life satisfaction using three survey questions asking about satisfaction with life overall, satisfaction with free time, and a rating of self-perceived productivity. Finally, Beyer et al. (2010) used the Comprehensive Quality of Life Scale, which measures material well-being, health, productivity, intimacy, safety, place in society, and emotional well-being. It is possible that the variability in measurement of quality of life led to different results among these studies.

The other three studies measured differences in quality of life in workers with intellectual disability in community (including supported) employment and either sheltered or no employment. Kober (2005) found that Australian workers in community employment reported higher quality of life than workers in sheltered employment. Another Australian study compared quality of life of people in competitive employment to people who were looking for work and found that workers reported a better quality of life (Eggleton et al., 2000). Verdugo et al. (2006), however, found no difference in quality of life between workers in community and sheltered employment in Spain. This research helps us begin to understand the relationships between employment and quality of life from an international perspective. More research is needed to understand these relationships in other countries, and explore contextual differences in employment settings and supports.

4.3 Limitations of research

This review highlights several shortcomings in intellectual disability employment research. Only one article in this study prospectively measured health or quality of life. Inge et al. (1988) used biometric markers to measure health. The authors measured the markers at the time of job attainment and again every three months. Prospective studies are important for understanding the direction and complexity of the relationship between health and employment. The current review highlights the need for prospective studies investigating the relationships between employment, health, quality of life, and closely related constructs. Further, much of the research on the general population points to a bidirectional relationship between employment and health (van der Noordt et al., 2014; Waddell & Burton, 2006). That is, employment promotes health, but also healthier people are employed more often. The dearth of prospective studies in the intellectual disability field prevents us from knowing if participation in employment does lead to better health.

Additionally, many of the articles included in this study had a small number of participants with intellectual disability. A likely reason could be the small number of people with intellectual disability who are employed. However, this limitation makes it difficult to understand the causal influences of employment and health. Large studies are needed to draw more conclusive results about the relationship between employment and health, and to document and measure change as people transition from segregated or no work to employment over time and as a function of job match and supports.