Workplace supports for employees with intellectual disability: A systematic review of the intervention literature

Abstract

BACKGROUND:

Competitive integrated employment often remains out of reach for people with intellectual disability. Consistently poor outcomes have resulted in research and policies promoting employment through the provision of workplace supports. Researchers have established a substantial body of intervention research addressing pre-employment supports. However, minimal intervention research exists addressing the provision of supports subsequent to job placement.

OBJECTIVE:

The objective of this study was to systematically examine the body of intervention research associated with workplace supports used to address career maintenance and career advancement for employees with intellectual disability.

METHODS:

A systematic literature review was conducted, examining intervention research published between 1984 and 2018. Fourteen studies met inclusion criteria. These studies included 85 employees with intellectual disability and 57 support providers (e.g., employment specialists, job coaches, co-workers).

RESULTS:

Results revealed evidence of interventions addressing career maintenance through the provision of training to both support providers and employees with intellectual disability. Training addressed workplace performance and social integration. No interventions were identified promoting career advancement.

CONCLUSION:

This paper offers an overview of the current intervention research base addressing workplace supports for employees with intellectual disability and makes recommendations for research, policy, and practice.

Keywords

Literature review intellectual disability employment workplace supports

1 Introduction

Meaningful employment is a defining goal of adulthood. Having a disability does not lessen the desire to achieve this goal (Migliore et al., 2007). Work allows employees with disabilities opportunities to learn new skills and sharpen existing ones (Wehman, 2011). The pay associated with competitive integrated employment secures economic well-being, thereby increasing the likelihood of self-sufficiency and the potential for upward mobility (Blackorby & Wagner, 1996). The benefits of work are not just monetary, as employment expands personal and professional networks, builds social connections, and expands community participation (Brown et al., 2006). Most importantly, consistent and valued work has a substantial influence on feelings of self-worth and emotional well-being (Kober & Eggleton, 2005; Schur, 2002). It is clear that disability should not deter a person from entering the workforce, finding meaningful work, and experiencing career advancements.

The number of people with disabilities who are employed remains discouragingly low; and is even more dismal for people with intellectual disability, such as those with significant limitations in intellectual functioning and adaptive behavior (Erickson et al., 2012; Schalock et al., 2010). In 2000, the National Organization on Disability conducted a survey on a national cross-section of 1,000 adults with and without disabilities. Results indicated that only 8% of adults with intellectual disability were employed in the year 2000 compared to 81% of those without disabilities. More recent data confirm outcomes remain essentially unchanged (Hall et al., 2011). Research has demonstrated that overwhelmingly, people with intellectual disability and their families prefer competitive (i.e., full-time or part-time employment where an employee receives commensurate wages), integrated (i.e., at a location where people without disabilities make up the majority of employees) employment (Migliore et al., 2007).

When people with intellectual disability are employed, they are often involved in precarious work, such that their jobs offer minimal benefits, few hours, and low wages (Benach et al., 2014; Steinmetz, 2006). Employees with intellectual disability are twice as likely to experience job loss, partly because their jobs have lower status and less stability (Kaye, 2009; Yelin & Trupin, 2003). Low-quality jobs have resulted in far greater periods of unemployment than counterparts without disability, causing employees with intellectual disability to experience difficulties related to sustaining employment after initial placement (Rumrill & Roessler, 1999). Employees with intellectual disability are also less likely than counterparts without disabilities to progress or advance through promotion or job expansions (Steinmetz, 2006). These limited employment circumstances are highly consequential for employees with intellectual disability, leading to substantially lower job security and higher rates of poverty (Schur et al., 2009), as well as social isolation and issues with psychological and physical health (Brand, 2015).

Poor employment outcomes have prompted national and state-level efforts promoting meaningful employment for people with intellectual disability. National legislation, such as the Developmental Disabilities Bill of Rights Act of 1984 (P.L. 98–527) and the Americans with Disabilities Act of 1990 (P.L. 101–336), has promoted employment access and engagement for people with disabilities. More recent legislation has focused specifically on competitive integrated employment. In 2014, Congress passed the Workforce Innovation and Opportunity Act (WIOA), funding state and local workforce initiatives that provide job training and related services to people facing employment barriers, including people with disabilities (P.L. 113–128). Numerous legislative efforts have also been made at the state-level. For example, Employment First, a policy and advocacy position established in 2012, encourages the full inclusion of people with significant disabilities in integrated employment (Cannella-Malone & Schaefer, 2015). These policies and initiatives support opportunities for people with disabilities to have meaningful community employment (Nord et al., 2013).

Another critical tactic for improving the employment outcomes of people with intellectual disability is the use of employment support interventions. One early intervention, supported employment, was promoted in the Developmental Disability Act of 1984 (P.L. 98–527) and the Rehabilitation Act of 1986 (P.L. 99–506). This intervention acknowledged the necessity of ongoing supports to people with disabilities to obtain and maintain employment. Supported employment is defined as competitive employment (i.e., full or part-time) for which wages paid are commensurate with coworkers’ earnings occurring in integrated settings where supported employees are working and interacting with co-workers without disabilities (Sima et al., 2015). This intervention calls for professionals to provide individualized and intensive assistance to employees with disabilities through (a) job development and placement, (b) job-site training and advocacy, (c) on-going assessment, and (d) follow-along employment services (Wehman, 2012). A more recent intervention is customized employment. Customized employment is a flexible process designed to personalize the employment relationship between a job candidate and an employer in a way that meets the needs of both (Parent, 2004). It is based on an individualized match between the strengths, conditions, and interests of a job candidate and the identified business needs of an employer.

In addition to providing specialized supports to employees with intellectual disability, employment support interventions also identify and utilize supports available within the employee’s work environment. These supports, known as natural supports, include assistance, relationships, and interactions that enable a person to secure, maintain, and advance in ways that correspond to the typical work routines and social actions of other employees (Rogan et al., 1993). Natural supports, which are both typically available and perceived as normative within the employee’s work environment, are provided by workplace resources (Butterworth et al., 1997). Although conceptualized differently throughout the literature, definitions of natural supports consistently emphasize typical settings, conditions, and features of employment as well as reliance on co-workers and other company personnel in designing and providing supports to employees with disabilities.

Although employment support interventions, such as supported and customized employment and the use of natural supports, have been established for over three decades, little research has been conducted examining how to effectively provide supports to employees with intellectual disability. The intervention research that does exist focuses primarily on strategies to support attainment of employment. However, the process of sustaining and advancing after a job is secured includes added complexities that have not been sufficiently examined. Considering that work is dynamic, changes in the work environment may necessitate changes to the types and frequency of supports provided to employees with intellectual disability (Bellamy et al., 1988). Workplace supports may be needed to ensure that an employee’s needs are met, thereby guaranteeing sustained employment with opportunities for career advancement (Berg et al., 1997).

The issue of supporting employees with intellectual disability to maintain and advance in careers is not new, however it appears to remain unanswered. Therefore, a systematic review of the literature is warranted. The purpose of this review is to identify intervention research related to the provision of workplace supports after an initial job placement is secured for an employee with intellectual disability. We sought not to document the magnitude of intervention effects or to compare the efficacy of different intervention approaches; but rather, to delineate the extent to which specific intervention strategies have been evaluated thus far and to characterize the overall quality of the studies comprising the literature. In doing so, we aimed to provide the field with information about the range of potential intervention strategies and to identify key gaps in the current knowledge base. To accomplish this, we sought to answer the following research questions:

What types of supports are used to promote career maintenance and advancement among employees with intellectual disability?

With whom and by whom have these supports been provided?

What is the methodological quality of the intervention research identified?

2 Method

We applied a structured approach to identify intervention research addressing the provision of employment supports by both support providers (e.g., job coaches/employment specialists) and natural supports (e.g., co-workers/managers) to employees with intellectual disability after initial job placement. In the following section, we describe the methods used to systematically examine the literature base, including inclusion criteria, literature search procedures, and coding methods.

2.1 Inclusion criteria

We selected studies based on six criteria. First, we included publications from peer-reviewed journals describing empirical, intervention-based investigations using group (i.e., experimental or quasi-experimental) or single-case designs. We excluded case reports, observational studies, qualitative studies, or other non-intervention studies. Second, we only included studies in which participants with a diagnosis of intellectual disability were included. We chose to limit the search, thereby excluding publications targeting employees with emotional, behavioral, learning, or physical disabilities, unless the publication also included participants with intellectual disability. Third, we only included studies in which employees were in high school through adulthood. Fourth, we only included studies occurring in integrated employment settings. We excluded any study conducted in a sheltered workshop or segregated or simulated work setting. Fifth, we only included studies examining outcomes related to career maintenance or advancement. We excluded studies focused on career development or job attainment. Finally, we only included studies published in English, peer-referenced print or online journals between January 1984 and June 2018. We selected 1984 as the start date because it marked the passing of the Developmental Disability Act (P.L. 98-527), which authorized the original provision of supported employment.

2.2 Literature search procedures

We employed a systematic approach to identify studies meeting the inclusion criteria. First, we performed electronic searches using the following databases: ERIC, EbscoHost, and PsycInfo. We utilized various combinations of keywords describing the population (i.e., intellectual disabilit*), domain (i.e., employment), and type of support (i.e., formal support, informal support, natural support, job coach, employment agency, and family support). Operational definitions of keywords are available from the lead author upon request. This initial search produced 487 articles. We reviewed titles to determine if the abstract should be read and evaluated for possible inclusion. Of the 487 articles, we excluded 431 because the study title: (a) related to other adult domains (i.e., independent living), (b) described supports provided to family members of people with intellectual disability (i.e., mothers), and (c) utilized non-intervention research methodologies (i.e., surveys and questionnaires). This resulted in 56 articles identified for subsequent abstract review. We reviewed the abstracts of each article to determine if the full article should be read and evaluated for inclusion. Of the 56 articles, we excluded 32 based on abstracts, primarily because abstracts described the use of non-intervention research methodologies; leaving the remaining 24 articles for a full article review.

Additionally, we performed a hand search of the Journal of Vocational Rehabilitation. This journal, which frequently publishes articles relevant to this review, was not available in the institution’s online library databases. Thus, a hand search was necessary. We reviewed issues published between the years of 1991, the journal’s first year of publication, through 2018. We reviewed the index of each issue to identify articles focusing on people with intellectual disability, workplace supports, and career maintenance or advancement. We then reviewed the title, abstract, method, and results sections of articles identified as potentially eligible to determine if the study met inclusion criteria. This resulted in the identification of 43 additional articles.

Among the 67 articles selected from the electronic search (n = 24) and hand search (n = 43), 14 were removed as duplicates, with the 53 remaining articles read in their entirety. After downloading and reading each article, 45 were removed. Twelve studies were excluded because they utilized a correlational design, while nine were removed because they utilized qualitative research methodologies. Ten additional articles were excluded because of issues with research design. More specifically, these articles (a) were practitioner papers, (b) were demonstration projects, or (c) used surveys or questionnaires. Fourteen articles were removed for other reasons, such as not including people with intellectual disability, not addressing career maintenance and advancement, or not focusing on workplace supports. This left a total of eight articles.

Finally, an ancestral search of the eight identified articles was conducted to identify additional articles meeting inclusion criteria not identified by either of the prior search methods. This led to the identification of five additional articles. One article provided results for two separate studies. Thus, fourteen empirical studies published in thirteen peer-reviewed articles were included in the final review. Figure 1 provides a flowchart of the search process.

Fig. 1

Summary of the literature search procedures.

2.3 Coding procedures

We coded each article twice. First, we coded each study according to a number of key elements (e.g., demographics, research design, and intervention characteristics). Key elements were coded using a researcher-developed coding sheet. When information was not available in an article, it was coded as not reported (NR).

The articles included in this review involved multiple groups of participants, including supported employees, job coaches, employment specialists, co-workers, and workplace managers. As a result, demographic information was coded for each participant group. For supported employees (i.e., employees with intellectual disability), demographic information included age, gender, disability, and race. Information regarding the supported employees’ jobs were coded for location, job duties, work hours, and job tenure. For support providers (i.e., job coaches/employment specialists and co-workers/managers), the demographic information included age, gender, race, job tenure, and educational level.

Next, we coded the research design based on whether the study was quantitative or mixed method. For quantitative studies, research method, research questions, independent and dependent variables, duration of the intervention, assessment measures, analysis procedures, treatment reliability, inter-observer agreement, maintenance, and social validity codes were collected if present. For mixed-methods studies, we coded both quantitative elements as described above as well as qualitative elements according to method, research questions, duration, location, and results.

Finally, we coded intervention characteristics. Training was an essential element of each study’s intervention. As a result, we coded training intervention’s according to content, methods, materials, recipient, trainer, location, and length. We also coded for intervention results, noting the location and length of data collection.

To answer the research question associated with methodological quality, we coded each study utilizing single-case or group design according to the Council for Exceptional Children’s Evidence-Based Practice Standards, a set of standards for identifying evidence-based practices in special education. CEC’s Evidence-Based Practice Standards, which were systematically vetted by expert special education researchers through a Delphi study, provide an integrated set of standards for classifying the evidence base of practices based on findings from both group design and single-case design studies (Cook et al., 2014). Standards for group design studies include 24 quality indicators, while standards for single-case design studies include 22 quality indicators. The standards for both single-case and group design studies address eight areas of research: (a) context and setting, (b) participants, (c) intervention agents, (d) description of practice, (e) implementation fidelity, (f) internal validity, (g) outcome measures/dependent variables, and (h) data analysis. If the study addressed a specific quality indicator, it received a score of “1.” If it did not address a quality indicator, it received a score of “0.” If the quality indicator did not apply to a particular study, it was marked as not applicable (NA). Each study’s score on individual quality indicators was totaled, divided by the total number of quality indicators, and multiplied by 100%.

2.4 Interrater reliability

Interrater reliability was established across all studies. The first and third authors compared each study item-by-item. Agreements and disagreements were recorded and used to calculate interrater reliability (i.e., number of exact agreements, divided by agreements plus disagreements). For key elements, the mean interrater reliability was 91.8% (range: 89.5% to 94.7%). For quality indicators, the mean interrater reliability was 93.3% (range: 81.8% to 100.0%). Consensus was met on disagreements.

3 Results

A total of 14 studies were included in this systematic review. Studies were published across nine journals between 1984 and 2016. The majority of studies (n = 8, 57.1%) were published before 2000, with four studies (28.6%) published between 1984 and 1989 and four studies (28.6%) published between 1990 and 1999. Three studies (21.4%) were published between 2000 and 2005, and three more were published between 2010 and 2016.

3.1 What types of supports are used to promote career maintenance and advancement?

Two types of supports emerged: (a) supports for workplace performance and (b) supports for social integration. All 14 studies addressed career maintenance. None of the studies incorporated an intervention to promote career advancement. Among the 14 studies, seven focused on improving workplace performance, six aimed to enhance social integration, and one intervened on both workplace performance and social integration. Most of the studies intervened by providing training (n = 11, 78.6%). Training was provided to job coaches/employment specialists (n = 4, 28.6%), co-workers/managers (n = 1, 7.1%), supported employees (n = 2, 14.3%), supported employees and co-workers/managers (n = 3, 21.4%), and job coaches/employment specialists and co-workers/managers (n = 1, 7.1%). Two studies (14.3%) intervened through contextual interventions, or changes to the work environment. One study utilized both training and contextual interventions (e.g., Hood et al., 1996). See Table 1 for a summary of the interventions’ key elements.

Table 1
Summary of Interventions’ Key Elements

Purpose of Support Type of Intervention Recipient of Intervention Intervention Design Intervention Features Location of Intervention Skills Address by Intervention

Study Workplace Performance Social Integration Training Contextual Intervention Supported Employees Employment Specialists Co-Workers/Managers Single-Case Group Mixed-Methods Maintenance Social Validity Worksite Online Other

Brock et al. (2016) X X X X X task analysis, simultaneous prompting, least-to-most prompting

Chadsey et al. (1997) X X X X X social interactions, employment integration, co-worker involvement

Chadsey-Rusch et al. (1984) X X X X X frequency of questions, topics initiated, topics continued, conversational ability

Farris &Stancliffe (2001) X X X X X X co-worker involvement

Gilson &Carter (2016) X X X X X X X X social interaction, task engagement, proximity of job coach

Hagner et al. (2014) X X X X X workplace culture, level of job coach support, job satisfaction, level of teamwork

Hood et al. (1996) X X X X X X X accuracy of task completion, supervisor satisfaction

Lee et al. (1997) X X X X X X types of social interactions, number of social interactions

Likins et al. (1) (1989) X X X X X X X accuracy, time

Likins et al. (2) (1989) X X X X X X X accuracy, time, quality control checking

McHugh et al. (2002) X X X X X vocational integration, social validation

Park &Gaylord-Ross (1989) X X X X X X social behavior of supported employees, social validation

Parsons et al. (2001) X X X X X X X job coach support, performance of supported employee

Storey &Garff (1997) X X X X X X X vocational integration, social validation

3.2 Training

Eleven studies assessed the impact of training support providers using single-case design (n = 8), group-design (n = 2), and mixed-methods (n = 1) to provide workplace performance and social integration supports. Support provider training covered a wide variety of topics and content, including workplace supports (n = 9), social integration strategies (n = 3), disability history and awareness (n = 2), contextual changes (n = 2), workplace culture (n = 1), and employment consulting (n = 1). Studies focused on workplace performance addressed prompting strategies, evaluation methods, and systematic instructional strategies (i.e., cueing, corrective feedback, reinforcement, fading, task analysis). For studies addressing social integration, training included content related to natural support strategies (e.g., asking questions, understanding workplace norms). Job coaches/employment specialists were the only group to receive training on employment consulting practices, while co-workers/managers were the only group to receive training on topics of disability awareness and disability history.

Overwhelmingly, the collected data was positive, demonstrating that the training interventions resulted in anticipated changes. Of the articles describing positive outcomes, they were described with varying levels of detail. Several of the studies described positive outcomes through statistical significance. In the following studies, all of the outcome measures were statistically significant: Hagner, Dague, & Philips (2014) and Farris & Stancliffe (2001). For studies not using statistical significance, positive outcomes were demonstrated through single-case design graphs. The following single-case studies demonstrated significant findings as reported by the authors: Brock, Page, & Seaman (2016); Gilson & Carter (2016); Hood, Test, Spooner, & Steele (1996); and Storey & Garff (1997). The remaining five studies demonstrated mixed results, meaning significant results were demonstrated on certain measures while non-significant results were obtained on others.

Seven studies assessed the impact of training supported employees using single-case design. Training provided to supported employees addressed both social integration (n = 3) and workplace performance (n = 4). Studies focused on social integration addressed the topics of question-asking, social behaviors, and social integration. Studies addressing workplace performance address the topics of accuracy, speed, quality control, and supervisor satisfaction. Three of the studies demonstrated positive results, meaning that the training interventions resulted in anticipated changes. Significant outcomes were demonstrated through single-case design graphs. The following single-case studies demonstrated significant findings as reported by the authors: Hood, Test, Spooner, & Steele (1996); Parsons, Reid, Green, & Browning (2001); and Storey & Garff (1997). The remaining four studies demonstrated mixed results, meaning significant results were demonstrated on certain measures while non-significant results were obtained on others.

3.3 Contextual interventions

To provide workplace performance and social integration supports, some studies in this review intervened through the use of contextual interventions (i.e., interventions altering the work environment to enhance supported employees’ performance). Two contextual interventions changed environmental aspects of the worksite. For example, Hood, Test, Spooner, and Steele (1996) implemented the use of visual supports detailing necessary environmental arrangements (e.g., specific tables, positions of workers relative to equipment). Contextual interventions were also used to increase social integration using an ecological model. Chadsey, Linneman, Rusch, and Cimera (1997) interviewed co-workers to gather information about the culture of the work setting (e.g., social customs, gathering places, celebrations, and work space). They then used this information to rate the supported employee’s level of social integration. After identifying discrepancies, the authors suggested possible contextual changes, such as having the supported employee take breaks at the same time as another co-worker, or changing the supported employee’s route from their workstation to the break room to interact with co-workers along the way.

3.4 To whom and by whom are supports provided?

Across the 14 studies, 85 supported employees with intellectual disability were provided supports by 57 support providers, including job coaches/employment specialists and co-workers/managers. In the following sections, we describe the characteristics of these two groups of participants. Summaries of these descriptions can be found in Tables 2 and 3.

Table 2
Demographics of Supported Employees (N = 85)

n (%)

Gender

Female 45 (52.9%)

Male 40 (47.1%)

Race/ethnicity

African American 1 (1.2%)

White 2 (2.4%)

Not specified 82 (96.5%)

Disability

Intellectual Disability 85 (100%)

Reported severity

Mild 8 (9.4%)

Moderate 1 (1.2%)

Severe 38 (44.7%)

Other descriptors (e.g., “moderate to severe) 38 (44.7%)

Job type

Food service 55 (64.7%)

Housekeeping/janitorial 11 (12.9%)

Office setting 5 (5.9%)

Cashiers 4 (4.7%)

Animals 2 (2.4%)

Grocery stores 2 (2.4%)

Customer service 2 (2.4%)

Education 1 (1.2%)

Retail 1 (1.2%)

Healthcare 1 (1.2%)

Dock assistant 1 (1.2%)

Job status

Part-time 54 (63.5%)

Full-time 2 (2.4%)

Not specified 29(34.1%)

	n (%)
Gender
Female	45 (52.9%)
Male	40 (47.1%)
Race/ethnicity
African American	1 (1.2%)
White	2 (2.4%)
Not specified	82 (96.5%)
Disability
Intellectual Disability	85 (100%)
Reported severity
Mild	8 (9.4%)
Moderate	1 (1.2%)
Severe	38 (44.7%)
Other descriptors (e.g., “moderate to severe)	38 (44.7%)
Job type
Food service	55 (64.7%)
Housekeeping/janitorial	11 (12.9%)
Office setting	5 (5.9%)
Cashiers	4 (4.7%)
Animals	2 (2.4%)
Grocery stores	2 (2.4%)
Customer service	2 (2.4%)
Education	1 (1.2%)
Retail	1 (1.2%)
Healthcare	1 (1.2%)
Dock assistant	1 (1.2%)
Job status
Part-time	54 (63.5%)
Full-time	2 (2.4%)
Not specified	29(34.1%)

Table 3

Demographics of Support Providers (N = 57)

	n (%)
Type of supports
Job coach/employment specialists	24 (42.1%)
Co-workers	18 (31.6%)
Managers	10 (17.5%)
Other employees	5 (8.8%)
Gender
Female	24 (42.1%)
Male	6 (10.5%)
Not Specified	27 (47.4%)
Race/ethnicity
African American	1 (1.8%)
European American	5 (8.8%)
Not specified	51 (89.5%)
Education
High school diploma	3 (5.3%)
GED	1 (1.8%)
Associate’s degree	2 (3.5%)
Bachelor’s degree	7 (12.3%)
Master’s degree	2 (3.5%)
Not specified	42 (73.7%)
Work experience
Experience	30 (52.6%)
No experience	6 (10.5%)
Not specified	21 (36.8%)

3.5 To whom are supports provided

People with severe intellectual disability were most frequently represented (n = 38, 44.7%) across all studies. A few participants were identified with mild (n = 8, 9.4%) and moderate (n = 1, 1.2%) intellectual disability. Authors used ranges, such as moderate to severe, to describe 38 supported employees. No persons were labeled with profound intellectual disability. Supported employees ranged in age from 16 to 73 years old and were evenly distributed between males (n = 40, 47.1%) and females (n = 45, 52.9%). Only one study reported race, and among the three subjects, two were white, and one was African American.

3.6 By whom are supports provided

Supports were provided by 57 support providers across the 14 studies, including job coaches/employment specialists (n = 24, 42.1%), co-workers (n = 18, 31.6%), managers (n = 10, 17.5%), and other employees (n = 5, 8.8%). Only one study targeting six job coaches reported race: five were white and one was African American. Level of education was only described for 15 job coaches/employment specialists, many of whom held a bachelor’s degree (46.7%). Most job coaches/employment specialists (93.7%) were experienced, with job tenure ranging from 16 months to 30 years.

3.7 What is the methodological quality of the intervention literature?

The majority of studies (n = 11, 78.6%) assessed the impact of interventions, directed at both supported employees and support providers, through the use of single-case design, with ten of the eleven studies utilizing multiple baseline or multiple-probe designs. Three studies (21.4%), conducted with both supported employees and support providers, utilized a combination of descriptive statistics, repeated measures ANOVA, and non-parametric analyses (i.e., Mann-Whitney U-Tests). One study aimed at job coaches/employment specialists implemented a mixed-methods approach, utilizing a combination of content-analysis and regression.

When coding single-case and group design studies according to CEC’s Evidence-Based Practice Standards, we assessed the percentage of quality indicators described in each study. The average percentage of quality indicators described in each study was 84.9%, with percentages ranging from 66.7% to 100%. Only two studies addressed every quality indicator. We also assessed the percentage of studies addressing each of the quality indicators, with percentages ranging from 0% to 100%. Seventeen of the quality indicators were addressed by 100% of studies. Studies consistently did not address: (2.1) participant description, (3.1) intervention agent description, (7.6) evidence of validity, and (8.3) appropriate effect size. See Table 4 for a detailed summary of described quality indicators.

Table 4
Summary of Quality Indicators Described

Quality Indicator Brock et al.(2016) Chadsey et al. (1997) Chadsey-Rusch et al. (1984) Farris &Stancliffe (2001) Gilson &Carter (2016) Hagner et al. (2014) Hood et al. (1996) Lee et al. (1997) Likins et al. (1) (1989) Likins et al. (2) (1989) McHugh et al. (2002) Park &Gaylord-Ross (1989) Parsons et al. (2001) Storey &Garff (1997) % of Studies addressing QI

1.1 Context and setting 1 1 1 1 1 1 1 1 1 1 1 1 1 1 100

2.1 Participant description 1 0 0 0 1 0 0 0 0 0 0 0 0 0 7.1

2.2 Participant disability or risk status NA 0 0 0 1 0 1 0 1 1 1 1 1 0 53.8

3.1 Intervention agent description 1 0 0 0 1 0 1 0 0 0 1 0 0 0 28.6

3.2 Training of Intervention agents 1 1 1 1 1 1 1 1 1 1 1 1 1 1 100

4.1 Description of intervention materials 1 1 1 1 1 1 1 1 1 1 1 1 1 1 100

4.2 Description of intervention materials 1 1 1 1 1 1 1 0 1 1 0 1 1 1 85.7

5.1 Implementation fidelity 1 1 1 0 1 0 1 1 1 1 0 1 1 1 78.6

5.2 Treatment dosage/exposure 1 0 1 0 1 0 1 1 1 1 0 1 1 1 71.4

5.3 Comprehensive assessment of fidelity 1 0 1 0 1 0 0 1 1 1 0 1 1 1 64.3

6.1 Systematic manipulation of independent variable 1 1 1 1 1 1 1 1 1 1 0 1 1 1 92.9

6.2 Baseline description 1 1 1 1 1 1 1 1 1 1 1 1 1 1 100

6.3 Limited access to treatment in baseline 1 1 1 1 1 1 1 1 1 1 1 1 1 1 100

6.4 Description of assignment to groups NA NA NA 1 NA 1 NA 1 NA NA NA NA NA NA 100

6.5 Three demonstrations of experimental effect 1 1 1 NA 1 NA 1 NA 1 1 1 1 1 1 100

6.6 Sufficient baseline length and pattern 1 1 1 NA 1 NA 1 NA 1 1 1 1 1 1 100

6.7 Control for common threats to internal validity 1 1 1 NA 1 NA 1 NA 1 1 1 1 1 1 100

6.8 Overall attrition NA NA NA 1 NA 1 NA 1 NA NA NA NA NA NA 100%

6.9 Differential attrition NA NA NA 1 NA 1 NA 1 NA NA NA NA NA NA 100

7.1 Socially important outcome variable 1 1 1 1 1 1 1 1 1 1 1 1 1 1 100

7.2 Dependent variable definition and measurement 1 1 1 1 1 1 1 1 1 1 1 1 1 1 100

7.3 Findings fully reported 1 1 1 1 1 1 1 1 1 1 1 1 1 1 100

7.4 Timing/frequency of outcome measures 1 1 1 1 1 1 1 1 1 1 1 1 1 1 100

7.5 Interobserver agreement 1 1 1 1 1 1 1 1 1 1 0 1 1 1 92.9

7.6 Evidence of validity NA NA NA 0 NA 0 NA 0 NA NA NA NA NA NA 0

8.1 Appropriate data analysis techniques NA NA NA 1 NA 1 NA 1 NA NA NA NA NA NA 100

8.2 Single-subject graph 1 1 1 NA 1 NA 1 NA 1 1 1 1 1 1 100

8.3 Appropriate effect size NA NA NA 0 NA 0 NA 0 NA NA NA NA NA NA 0

% of QIs identified 100 77.3 86.4 66.7 100 66.7 91.0 81.8 91.0 91.0 68.2 91.0 91.0 86.4

Quality Indicator	Brock et al.(2016)	Chadsey et al. (1997)	Chadsey-Rusch et al. (1984)	Farris &Stancliffe (2001)	Gilson &Carter (2016)	Hagner et al. (2014)	Hood et al. (1996)	Lee et al. (1997)	Likins et al. (1) (1989)	Likins et al. (2) (1989)	McHugh et al. (2002)	Park &Gaylord-Ross (1989)	Parsons et al. (2001)	Storey &Garff (1997)	% of Studies addressing QI
1.1	Context and setting	1	1	1	1	1	1	1	1	1	1	1	1	1	1	100
2.1	Participant description	1	0	0	0	1	0	0	0	0	0	0	0	0	0	7.1
2.2	Participant disability or risk status	NA	0	0	0	1	0	1	0	1	1	1	1	1	0	53.8
3.1	Intervention agent description	1	0	0	0	1	0	1	0	0	0	1	0	0	0	28.6
3.2	Training of Intervention agents	1	1	1	1	1	1	1	1	1	1	1	1	1	1	100
4.1	Description of intervention materials	1	1	1	1	1	1	1	1	1	1	1	1	1	1	100
4.2	Description of intervention materials	1	1	1	1	1	1	1	0	1	1	0	1	1	1	85.7
5.1	Implementation fidelity	1	1	1	0	1	0	1	1	1	1	0	1	1	1	78.6
5.2	Treatment dosage/exposure	1	0	1	0	1	0	1	1	1	1	0	1	1	1	71.4
5.3	Comprehensive assessment of fidelity	1	0	1	0	1	0	0	1	1	1	0	1	1	1	64.3
6.1	Systematic manipulation of independent variable	1	1	1	1	1	1	1	1	1	1	0	1	1	1	92.9
6.2	Baseline description	1	1	1	1	1	1	1	1	1	1	1	1	1	1	100
6.3	Limited access to treatment in baseline	1	1	1	1	1	1	1	1	1	1	1	1	1	1	100
6.4	Description of assignment to groups	NA	NA	NA	1	NA	1	NA	1	NA	NA	NA	NA	NA	NA	100
6.5	Three demonstrations of experimental effect	1	1	1	NA	1	NA	1	NA	1	1	1	1	1	1	100
6.6	Sufficient baseline length and pattern	1	1	1	NA	1	NA	1	NA	1	1	1	1	1	1	100
6.7	Control for common threats to internal validity	1	1	1	NA	1	NA	1	NA	1	1	1	1	1	1	100
6.8	Overall attrition	NA	NA	NA	1	NA	1	NA	1	NA	NA	NA	NA	NA	NA	100%
6.9	Differential attrition	NA	NA	NA	1	NA	1	NA	1	NA	NA	NA	NA	NA	NA	100
7.1	Socially important outcome variable	1	1	1	1	1	1	1	1	1	1	1	1	1	1	100
7.2	Dependent variable definition and measurement	1	1	1	1	1	1	1	1	1	1	1	1	1	1	100
7.3	Findings fully reported	1	1	1	1	1	1	1	1	1	1	1	1	1	1	100
7.4	Timing/frequency of outcome measures	1	1	1	1	1	1	1	1	1	1	1	1	1	1	100
7.5	Interobserver agreement	1	1	1	1	1	1	1	1	1	1	0	1	1	1	92.9
7.6	Evidence of validity	NA	NA	NA	0	NA	0	NA	0	NA	NA	NA	NA	NA	NA	0
8.1	Appropriate data analysis techniques	NA	NA	NA	1	NA	1	NA	1	NA	NA	NA	NA	NA	NA	100
8.2	Single-subject graph	1	1	1	NA	1	NA	1	NA	1	1	1	1	1	1	100
8.3	Appropriate effect size	NA	NA	NA	0	NA	0	NA	0	NA	NA	NA	NA	NA	NA	0
% of QIs identified	100	77.3	86.4	66.7	100	66.7	91.0	81.8	91.0	91.0	68.2	91.0	91.0	86.4

We also coded studies for treatment reliability, inter-observer agreement, maintenance data, and social validity. Nine studies reported on treatment reliability, while ten studies reported inter-observer agreements. Less than 30% of studies (n = 4) collected maintenance data. Less than half of studies (n = 6) collected social validity data.

4 Discussion

The purpose of this systematic literature review was to better understand career maintenance and advancement for employees with intellectual disability. To accomplish this, we characterized the intervention literature base describing the provision of workplace supports after initial job placement. Findings from this review highlight several considerations, complexities, and challenges associated with the provision of such supports. Four critical issues emerged from the results. These issues, described below, relate to the focus of the literature, descriptions of supported employees, descriptions of support providers, and the methodological quality of the literature base.

4.1 Limitations

Prior to discussing the results of this systematic literature review, it is important to explain search and analysis decisions and how they may have limited the conclusions drawn. First, we only included intervention-based research found in educational and psychological databases. It is possible that including correlational literature could have revealed additional research useful in answering our review’s research questions. Second, our review focused on characterizing the current intervention literature base. It did not consider the magnitude of intervention effects or the efficacy of different intervention approaches. Although outside of the scope of the current review, these are important topics that should be addressed by future research.

Several elements of the studies included within this review also influenced its results and conclusions. The majority of included studies utilized single-case research designs carried out with as few as one or two participants. The external validity of these studies may be limited, as intervention effects are not sufficiently replicated across multiple participants, settings, or skills. Also, including studies from a nearly three-decade time span opened this review to inconsistencies in understandings of intellectual disability and research design standards.

4.2 Workplace supports are limited

The results of this systematic literature review found that all studies focused only on career maintenance, as evidenced by interventions’ focus on workplace performance and social integration supports. The studies confirmed the importance of accessing workplace performance supports for successful employment outcomes among employees with intellectual disability as established from prior research (Brady & Rosenberg, 2002; Cannella-Malone & Schaefer, 2015; Rogan et al., 2000). A person’s ability to perform the essential work tasks of a job influences the likelihood that they access competitive integrated employment (Heller et al., 2005). Results also confirmed previous literature espousing the importance of social integration as a critical element of integrated employment (Brickey et al., 1985; Butterworth & Strauch, 1994; Chadsey, 2007). It has been consistently demonstrated that employees with disabilities who are socially included at work are more likely to maintain their employment (Agran et al., 2016). Unfortunately, this systematic review did not identify a single study connected to career advancement. The degree to which workplace performance and social integration improve the likelihood of career advancement remains unanswered.

What this systematic literature review did reveal was the critical role of training to the provision of workplace supports. Training was an essential element in all of the intervention studies, most often targeted at support providers (i.e., job coaches, employment specialists, co-workers, managers). This finding does not come as a surprise, as past research revealed that quality employment supports are dependent upon the education and training of providers (Butterworth et al., 2012; Novak et al., 2014). Ongoing training has been identified as essential for providing quality supports to employees with intellectual disability (United States Department of Health and Human Services, 2017). It is known that supported employment programs report difficulties in finding appropriate training for support providers (Test et al., 2004). Furthermore, Test and colleagues found that available training programs are often driven by compliance regulations, prescribed topics, or annual reviews of specific information, not by the demands of the worksite or the needs of support providers.

Developing comprehensive, cohesive, and cost efficient training systems are needed, given the importance of training as well as the difficulties in finding, providing, and financing training for employment providers. The results of this systematic review demonstrate that training support providers, whether job coaches or co-workers, leads to enhanced employment outcomes. This information can be used by employment agencies and policymakers when advocating for policy changes to ensure a high quality provision of training.

Our findings also have implications for practitioners, including support providers and supported employment programs. Research has indicated that the quality of workplace supports is dependent upon the skill level of the support provider (Grossi et al., 1991). The results of this systematic literature review demonstrate that the provision of training does enhance the skills of support providers. As adult agencies continue to develop programs for employees with intellectual disability, it is imperative they prioritize training among support providers, including job coaches, employment specialists, co-workers, and managers. They should focus specifically on how they administer trainings and ensure the content of training extends beyond learning a job and increasing social inclusion to training promoting career advancement.

4.3 Limited understanding of those receiving and providing supports

The studies included in this literature review did not sufficiently describe supported employees in regards to their racial/ethnic backgrounds. Of the fourteen studies, only one reported the race of three participants. A lack of information about race potentially masks larger issues reported previously, such as underutilized employment services among people with disabilities who are culturally and linguistically diverse. This is particularly evident among formal programs providing employment supports, such as Vocational Rehabilitation (Middleton et al., 1996; National Council on Disability, 1999). When people with disabilities who are culturally and linguistically diverse do access employment services, they are more likely to experience disparities in the services received and outcomes achieved (Taylor-Ritzler et al., 2010). Researchers have identified several potential disparities, including cultural groups’ lack of trust in governmental institutions and racial mismatches between service providers and supported employees (Taylor-Ritzler et al., 2010). The lack of robust demographic data found among the studies in this literature review may mask this potential issue. In the future, defining and describing participants is clearly needed.

The second research question also focused on the staff providing employment support. Literature review results were able to ascertain the level of education of formal support providers (i.e., job coaches/employment specialists), but not those of the informal supports (i.e., co-workers/managers). Most job coaches held a bachelor’s degree, with some holding even higher degrees. For example, Gilson and Carter (2016) included three job coaches in their study, all of whom had a bachelor’s degree or master’s degree in special education. Formal support providers also had a significant amount of related work experience. Almost all (94%) job coaches and employment specialists had prior experience, ranging in length from 16 months to 30 years. The fact that employment providers were well-educated and experienced may have influenced their proficiency in facilitating supports, independent of the training they received. More effective staff, such as those with higher levels of education and greater amounts of training, translate into better outcomes for people with disabilities, a factor that may have influenced results and impacted generalizability (Wehman & Targett, 2002; Butterworth et al., 2012).

Unlike the job coaches and employments specialists included in these studies, the national picture illustrating the quality of job coaches and employment specialists is not as robust, with most working with little to no formal training (Grossi et al., 2001; Hagner et al., 2002: Novak et al., 2014). Researchers should make efforts to conduct research with all support providers, even those without relevant training or experience, solidifying our understanding of the types of training required for successful provision of employment supports.

4.4 Methodological quality of research methods

Several concerns emerged regarding the methodological quality of the studies included in this review. Using CEC’s Evidence-Based Practice Standards, it was revealed that the average percentage of quality indicators identified by each study was 84.9%, with percentages ranging from 66.7% to 100%. Results also identified the percentage of studies addressing each of the quality indicators, ranging from 0% to 100%. Seventeen of the quality indicators were addressed by 100% of studies. Of concern was the finding that only 7% of the studies adequately described study participants and only 28.6% adequately described intervention agents. Another concern relates to the fidelity of implementation. Authors inconsistently reported information regarding the fidelity of intervention implementation, hampering the strength of results. Less than 65% of studies reported treatment fidelity. Similarly, generalization and maintenance results were not found, with less than 30% of studies examining maintenance of learned skills. When study’s considered maintenance data, it was most often collected immediately following stabilization of data. Only two studies collected generalization or maintenance data after sufficient passing of time, in both instances six months later. Considering the long-term effects of training interventions toward demonstrating that supported employees can obtain new skills and maintain the skills already acquired, generalization and maintenance data are a possible marker of career advancement. It was impossible to understand whether initial workplace performance interventions were sufficiently robust in supporting potential career advancement.

Given the range of years of the published studies, it is not surprising that early research did not adhere to CEC’s Evidence-Based Practice Standards, which were published more recently. Future research should adhere to the field’s research standards, describing participants and procedures to ensure generalizability, maintenance, and replication. Studies targeting employment maintenance and advancement are only truly effective if participants, both supported employees and support providers, maintain acquired skills over time and generalize them to new environments. Finally, researchers should also more frequently assess social validity, given the importance of understanding which supports are effective by acknowledging the perspectives of those who use them (Wood & Steele, 1992).

4.5 Conclusion

The results of this review revealed interventions used to successfully train support providers and supported employees to learn initial workplace performance skills, as well as increase social integration within competitive integrated employment. However, the degree to which these interventions support employees with intellectual disability in maintaining or advancing within their career remains unknown. Scant research is available regarding the quality of workplace supports provided to employees with intellectual disability, despite enhanced policies and increased initiatives promoting improved employment outcomes for this group. Given the consequences of unsuccessful employment, it is our hope that the results of this literature review will be used to promote positive action on behalf of people with intellectual disability in the workplace and facilitate advancements in research, policy, and practice.

Conflict of interest

The author(s) declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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	Purpose of Support		Type of Intervention		Recipient of Intervention			Intervention Design			Intervention Features		Location of Intervention			Skills Address by Intervention
Study	Workplace Performance	Social Integration	Training	Contextual Intervention	Supported Employees	Employment Specialists	Co-Workers/Managers	Single-Case	Group	Mixed-Methods	Maintenance	Social Validity	Worksite	Online	Other
Brock et al. (2016)	X		X			X	X								X	task analysis, simultaneous prompting, least-to-most prompting
Chadsey et al. (1997)		X		X		X		X					X			social interactions, employment integration, co-worker involvement
Chadsey-Rusch et al. (1984)		X	X		X		X						X			frequency of questions, topics initiated, topics continued, conversational ability
Farris &Stancliffe (2001)	X		X				X		X				X	X		co-worker involvement
Gilson &Carter (2016)	X	X	X			X	X				X	X	X			social interaction, task engagement, proximity of job coach
Hagner et al. (2014)	X		X			X			X					X		workplace culture, level of job coach support, job satisfaction, level of teamwork
Hood et al. (1996)	X			X	X		X	X		X			X			accuracy of task completion, supervisor satisfaction
Lee et al. (1997)		X	X			X	X		X					X		types of social interactions, number of social interactions
Likins et al. (1) (1989)	X		X		X		X	X				X	X			accuracy, time
Likins et al. (2) (1989)	X		X		X		X	X				X	X			accuracy, time, quality control checking
McHugh et al. (2002)		X	X			X		X					X			vocational integration, social validation
Park &Gaylord-Ross (1989)		X	X		X			X			X	X				social behavior of supported employees, social validation
Parsons et al. (2001)	X			X	X			X			X	X			X	job coach support, performance of supported employee
Storey &Garff (1997)		X	X		X		X	X		X			X			vocational integration, social validation