Abstract
BACKGROUND:
People with intellectual disability are likely to face long-standing employment barriers in finding and keeping jobs, for a variety of reasons. This study, therefore, investigated barriers to employment of people with intellectual disability. The participants in this study were made up of sixty-five stakeholders who were recruited from six different categories.
OBJECTIVE:
The objective of the study was to determine barriers to employment of people with intellectual disability.
METHODS:
A qualitative and quantitative research design was used in the study. The qualitative method was used to systematically identify barriers to employment for people with intellectual disability while the quantitative method was used to rank the barriers.
RESULTS:
Findings indicate that barriers to employment for people with developmental disabilities are discrimination, stigma, employers’ attitude, and management style, feeling unappreciated, and working environment such as culture to accommodation, understanding and strengths. Moreover, results shows that discrimination was ranked the highest while feeling unappreciated was ranked the least of the barriers to employment of people with intellectual disability.
CONCLUSION:
The paper provides information about barriers to employment of people with intellectual disability in Nigeria that is required to initiate change in policy development.
Introduction
The attitude of employers plays a major role in determining employment. In identifying critical barriers and factors that facilitate employment, the experiences of people with disabilities provide valuable insight [1]. Employers and peer attitudes at the workplace may be linked to the interest of individuals with disabilities in working with most showing a strong sense of social distance towards those with disabilities [2]. The effect of such attitude is that people with disabilities, particularly those with intellectual disability, are confronted with systemic and enduring job obstacles, resulting in lower employment rates, and lower incomes compared to people without disabilities [3, 4]. Moreover, individuals with disability are viewed as helpless, lacking the ability to develop, and incapable of achieving comparable levels of performance as their colleagues in the work environment because of social distance [2].
The implication of such view on a global scale is that the income inequality among individuals with disabilities in comparison to that of the general population is much lower [5]. It is worth noting that unemployment among individuals with disabilities is lower in countries where human rights laws are enforced appropriately making it mandatory for organization to ensure that a proportion of the work force are individuals with special needs. According to Hästbacka, Nygård, and Nyqvist [6], employment is considered a mode of societal participation that extends far beyond economic sustainability. For this reason, employment can be regarded as a pursuit that enables an individual effective participation in productive activities, socialise with others, and achieve economic independence. Indeed, working can be describe as one way to minimise alienation and an effective tool for poverty reduction [7].
Considering, however, that most individuals with disabilities can – and want to – work, one might argue that unemployment rates in countries where policies protecting the rights of people with disabilities are not enacted are significantly higher [8]. Most developed countries are dealing with an aging population, which increases the prevalence of disability among employees [9]. Dealing with disability will become more of a concern as the workforce ages. The degree to which these changes impact economic growth is heavily dependent on labor participation [10]. Moreover, findings show that employment of people with intellectual disability is important, because of the long-term health-promoting effects it has on them [11]. Disability and unemployment issues have piqued the interest of world leaders on a global scale due to the critical role both would play in achieving the Sustainable Development Goals, one of which is the eradication of extreme poverty across all dimensions [12].
Optimizing employment outcomes for people with disabilities in low- and medium-income countries requires understanding the factors hindering and facilitating employment. Research on this topic is currently limited to high-income countries [13–15]. This study, therefore, investigated the barriers to employment of people with intellectual disability.
Literature review
Benefits of employment for people with intellectual disability
Individuals with stigmatized impairments (such as those with cognitive/intellectual, psychosocial/mental disorders) often face a great deal of difficulty finding employment [16]. However, the data regarding employment of people with disabilities in low- and middle-income countries such as Nigeria is not readily available [17]. There has, however, been research in Europe and the United Kingdom which found that employment has benefits for people with intellectual disability in terms of their wellbeing, independence, life experience, self-esteem, and satisfaction [5, 18], thus providing an efficient correlation between an employer’s expectations and a worker’s support and accommodation needs [19]. On the other hand, in low- and medium-income countries in Nigeria there is paucity of research regarding the economic participation of people with disabilities [20, 21].
Participation in the labour force for individuals with intellectual is strongly linked with several positive outcomes. People with intellectual disability who work have more influence over their lives, according to the findings, which increases results on self-determination, autonomy, and empowerment indicators [22, 23]. Improvement in the living standard of individuals with intellectual disability was also reported in terms of their wellbeing and self-esteem [22–24] and daily living skills, such as independent living, literacy, and communication skills [22–24]. The big question is: Who has access to this type of work and how simply it is for them to do it? According to research findings, those who excel and have the best chances of success at work are often those who require less social support, and who already live a healthier lifestyle, as well as the skills for independent living prior to starting work [22, 24].
People with intellectual disability can be employed in a variety of work environments. It can either occur in a sheltered or integrated environment [25]. According to systematic literature reviews, however, people with intellectual disability tend to be more satisfied with their jobs when they are integrated into a competitive employment environment [26, 27]. The importance of work to people with intellectual disability is highlighted in several studies, such as a vital part of their community participation, a supply of social connections, and an opportunity to feel appreciated [28, 29]. In addition, employed people can use and expand their skills, which increases social opportunities and the amount of time they can spend with others [30].
Employment disparities and barriers to employment
Several studies [31, 33] have found that employers have a widespread negative perception about people with disabilities job productivity, as well as employers’ lack of knowledge about disabilities and appropriate accommodation techniques. Other studies have identified the nature of the condition as a limiting factor for work, with mental disorders highlighted as aggravating employability [31, 34]. On average, people with disabilities work in lower-paying jobs with little to no potential for advancement and inadequate job security [35, 36]. Furthermore, when people with intellectual disability work, they are occasionally subjected to hazardous working conditions. Women with disabilities face even more employment challenges compared to men [37] The World Health Organization (WHO) reported that employment rates were lower for men with disabilities (53%) when compared with those without disabilities (65%) [5]. Such employment is frequently criticised for the practice of segregating people with disability from the rest of society, and for paying wages well below the minimum [38].
In Nigeria, the situation of people with disabilities is the same as in other developing countries. According to Ofuani [39], individuals with disabilities in Nigeria face barriers to participation in society and are marginalized, with few or no opportunities to express themselves and contribute to their own, or the nation’s development. Concerns regarding the costs of recruiting people with disabilities are seen as major barriers to labour market inclusion [40, 41]. Such barriers include a lack of comprehensive facilities and available infrastructure, as well as a lack of existing relationships between employees and employers [37]. With previous findings supporting the assumption that employers are averse to recruiting people with disabilities concentrate on a variety of impediments [42, 43]. In addition, factors related to job inequalities faced by people with intellectual disability may be narrowly classified as: (1) personal factors, such as the individual’s health and functional skills [44], as well as career preferences [45]; (2) environmental or contextual factors, such as trends in the labor market [46], and employer attributes, such as willingness to employ and accept people with disabilities [47]; and (3) social and policy-related factors, such as prejudice and discrimination against people with disability [48], and lack of accessible transportation [43].
Most of the research on employment barriers faced by people with intellectual disability has focused on individual barriers related to support criteria (e.g., attention and attitude), personality (e.g., motivation), or workplace interpersonal relationships (e.g., poor work quality and disagreements with coworkers) [49]. Few studies have taken a comprehensive approach to investigating why it is difficult for people with intellectual disability to find and sustain employment for reasons that do not stem from their own level of experience or characteristics but are related to the system and society to which they belong. Although some findings have identified barriers related to social stigma about disability [50], such research is, however, generally limited.
Methods
Research design
The study adopted quantitative and qualitative exploratory sequential approach to analyse barriers to employment of people with intellectual disability. Qualitative approach was used to elicit information from stakeholders and people with intellectual disability who participated in in-depth, semi-structured interviews. Data was collected during a one-day event in January 2021, from various stakeholders to obtain a greater understanding of the job experiences and challenges faced by people with intellectual disability. During the interviews, participants were asked to identify barriers encountered by people with intellectual disability to finding, maintaining, and changing jobs. Furthermore, the quantitative method was used for ranking the barriers (themes) identified by stakeholders.
Participant recruitment, sampling, and arrangement
Purposive and convenience sampling methods were used to select event participants who were identified as stakeholders, gatekeepers, knowledge brokers, or leaders on issues related to people with intellectual disability. This was based on the researchers’ personal experiences with people with disabilities. Sixty-five stakeholders were recruited from six different categories: (1) people with mild intellectual disability and their families/caregivers (N = 16); (2) employers (N = 8); (3) vocational training professionals (N = 7); (4) non-profit organisations and other disability serving organisations (N = 11); (5) decision and policy makers (N = 8); and (6) researchers and academics (N = 15). Participants had prior experience working with, hiring, or providing support services for people with intellectual disability, as well as living with them. Sixty percent of the participants were female, while forty percent were male.
The first group consisted of family members/caregivers (N = 8) and people with intellectual disability (N = 8). Families and caregivers were involved as caregivers as well as intermediaries for people with intellectual disability. The small sample size of people with intellectual disability was due to their unique attributes [51]. The Slosson Intelligence Test was used to screen participants with intellectual disability to identify those who had mild intellectual disability.
There were also participants who wore more than one cap (parents and any other stakeholder participating in the study) and provided information on behalf of family members (N = 7). They were listed organised into primary stakeholder groups but were not included in the overall category one. The participants were not related to one another. Stakeholders were also chosen from those involved in the delivery of support services and policy development for people with intellectual disability. Exclusion criteria included individuals who refused to sign the informed consent form, those whose residence was not within the study area, and individuals whose work was beyond the territorial and policy boundaries of the Lagos state, Nigeria.
Following the event, researchers used a third-party disability organization gatekeeper to recruit only people with intellectual disability for a focus group discussion (N = 8), rather than their relatives or caregivers. This was done to ensure openness and response from different perspective because some participants may not be willing to express their views where family members are present. The research team later presented event findings to a group of clients of this gatekeeper organization, which aided in the development of relationships and access among research participants. The factors identified were rated by stakeholders in special education who were not part of the discussion.
Research trustworthiness
Research rigor or trustworthiness is the degree of confidence in data, interpretation, and methodologies used to ensure the quality of the study [52]. The researchers of each study should establish the procedures and protocols necessary for them to be considered worthy of the reader’s attention [53]. The following are four ways to ensure trustworthiness of the qualitative data obtained.
Credibility
Merriam [54] defines credibility as “the degree to which the findings conform to reality.” Lincoln and Guba [55] argue that establishing credibility is among the most important factors in establishing trustworthiness. Researchers use multiple methodologies to increase credibility. These include triangulation, composing broad notes, member checking, peer review, reasoned agreement, and audit trail [55]. The validity of the results was ensured by taking extensive notes during the interviews and checking with members.
We provided everyone approached with the opportunity to decline to participate in the project to ensure that information collection sessions include only those genuinely willing to participate and offer information without reservation. Researchers demonstrated that there are no correct responses to the questions asked. By doing so, participants felt more comfortable sharing their experiences [56]. We included an informed consent form, voluntary interest and ensured the participants’ privacy in this study [56]. Additionally, we informed participants with intellectual disability and their caregivers that their participation would cause no harm.
Transferability
A study’s transferability refers to its ability to be applied to other situations [57]. It is essential to understand qualitative research results within the context of the organisation’s specific characteristics or association, including the geological region in which the research was conducted [58, 59]. The information was collected entirely from sixty-five stakeholders providing services to individuals with intellectual disability. Six categories of participants were recruited: people with mild intellectual disability and their families/caregivers, employers, vocational training professionals, non-profit organisations and other disability-serving organisations, decision and policy makers, and researchers and academics.
This study focused on views and responses of research members to be collected employing in-depth individual interviews. After which, the identified barriers were rated by stakeholders who were not part of the interview. The study was limited to a short period to gather information. A limited number of participants were carefully selected to take part in the discussion. We designed the questionnaire so that only opinions about barriers to employment for individuals with intellectual disability were collected. Furthermore, it was our responsibility to see relations and conceivable transferability outcomes in the research discoveries.
Dependability
This addressed the issue of reliability more directly by reporting the study process in detail, permitting future researchers to replicate a similar study. Lincoln and Guba [55] stress the close ties between credibility and dependability, arguing that, in practice, a demonstration of the former goes some distance in ensuring the latter. The study dependability was ensured by engaging a researcher who was not involved in information gathering, data collection or analysis, and the study’s findings to conduct an inquiry review. We examined the exactness of the findings to verify that they (the findings) were substantiated by the data collected. It was determined whether the data itself supports all translations and conclusions.
Confirmability
According to Patton [60], confirmability is like the concept of objectivity in qualitative research. Miles and Huberman [61] consider the degree to which the researcher admits his or her own bias to be a critical determinant of confirmability. Therefore, the convictions that underlie choices made and strategies received will be acknowledged in the research report. Depending on the data collection strategies, such as open-ended questions, some respondents may find it difficult to provide detailed responses. Most respondents do not answer all questions during the survey.
After the interview, the researcher should ensure that notes regarding personal feelings, biases, and experiences are taken immediately. Whenever possible, questions were repeated so that the answers were consistent. Additionally, we made sure notes were taken about personal feelings, biases, and insights immediately following the interview. The researchers also ensure accuracy by being a follower rather than leading the interview by asking for clarifications whenever necessary.
Method of data analysis
Qualitative data obtained was transcribed verbatim and thematically analysed to identify the barriers encountered by the people with disabilities while numerical data obtained via survey was analysed descriptively using mean, standard deviation, frequency and percentage to rank the barriers as identified in the qualitative data.
Ethical consideration
In accordance with research ethics, a printed consent form written in English was given to each participant. After ensuring sufficient comprehension, each participant completed and signed the consent form. Participants were told that their profiles and answers would be kept private. Thus, the study adhered to the ethics of research confidentiality.
Results
This section summarises the findings regarding the social barriers that people with intellectual disability encounter while seeking employment. Since there is a need to broaden the scope of current literature to include mechanisms that promote improved job outcomes, the results in this article concentrate on barriers to employment presented. This is done to identify the barriers so that they can be tackled. It is important to note, however, that people with intellectual disability also talked about the facilitators of their employment and the help they received to find and keep jobs.
Discrimination
Participants in the focus group discussion, including people with intellectual disability, reported that they encountered subtle discrimination. This discrimination was complicated by the fact that they were sometimes employed to do work in positions which were generally referred to as detrimental to their health and derogatory to their person. The implications are that the jobs were usually non-pensionable, subject to danger, casual, low-paying, and without any benefits. Some participants noted that people with intellectual disability were treated the same as other workers without consideration of their intellectual functioning and adaptive skill areas, although, people with intellectual disability stated that some employers did show empathy to them while performing assigned tasks. For example, one man expressed that he felt discriminated against when he did not receive a formal explanation for being laid off: “The organisation felt I should be able to figure things out myself, so no reason was given for no longer offering casual shifts to me. All I was told is that ‘you will be contacted when your services are needed again” (Person with mild intellectual disability).
Another participant offered: “Others were offered full time employment, and when she asked why one person with intellectual disability was still offered a casual job, she was told that, ‘She cannot be placed in a position that will allow her to interact with clients coming to the organisation because of policy’” (Vocational training professional).
One noted that he was discriminated against because of his disability and was also accused of things that he did not do. He illustrated this, saying: “When something spill on the floor, you will hear other worker saying ‘Ask ‘A’ because of his shaking hands if he did it’. If I tell them I did not someone will respond that ‘who else is having similar condition with you in this organisation?”’ (Person with mild intellectual disability).
One of the employers noted that he doesn’t see any reason of employing a person with intellectual disability. The employer was asked the reason. His response was that “this group of people should depend on others since they have been identified as intellectually disable and what contribution will they be making to the organization when given such employment” (Employer).
Stigmatization
Participants in the focus group discussion identified stigma as a barrier to employment of people with intellectual disability. Stigma is a broad concept, and it can be experienced in both the workplace and in society. Stigma is also referred to as a prejudice or negative perception which has negative impact on the productivity of people with intellectual disability.
As one of the persons with intellectual disability reported to a stakeholder that: “He was instructed on his first day on the job to always stay where clients will not be able to see him if he wants to stay long on the job while failure to do that is an indication that he is not interested in keeping the job” (Non-profit organisation).
It pointed out by an employer that “the only reason an individual with intellectual disability will be instructed to stay from clients is because staying around clients will be an embarrassment to the organization with negative implication on such business” (Employer).
Another one noted that he had to intervene when he heard an employee refers to an employed person with individual disability as “you rather than calling the person by her name and most time used funny words to describe the lady whenever she tries explaining situation of things in the work environment” (Policy maker).
Some of the common inherent social limitations included perverse incentives, transportation barriers, and negative public opinion. An example reported by a respondent was: “When she was told that there is no need for salary increase for a person with intellectual disability because they do not need such money” (Families/caregivers of people with intellectual disability).
One of the stakeholders noted that she was asked: “Why are you so concerned about their welfare? You should understand that we are only doing them a favour by employing them because no organisation in this community will be willing to accept them as employer” (Researchers and academics).
Participants reported that their employers’ lack of knowledge and appreciation of people with intellectual disability, as well as their fear of the unknown, contributed to stigma.
Employers’ attitude and management style
According to participants, employers downplay the skills of people with intellectual disability, while emphasising their weaknesses. This has kept them from progressing in the workplace in the same way as those without intellectual disability.
For example, one participant said, “...he was told by one person with intellectual disability that he has to wait for others to arrive before he can start his job, even if he gets to the office early because they feel he cannot be trusted alone in the office” (Person with intellectual disability).
Sample population
Sample population
One stakeholder reported that a person with intellectual disability was told to “Stop acting as if you know anything or else you will be told to go home. You look at how others are doing it and that it all that is expected of you” (Person with intellectual disability). When he tried to find out the reason for such a statement, he was told, “I am the boss and you do as told without questioning my authority” (Vocational training professional).
A stakeholder explained that the reason for such a statement was: “Because most employers are of the opinion that people with intellectual disability do not possess the skills required to handle a task on their own and where that is exhibited, they feel it is a fluke” (Researcher/Academia).
Participants also described the insensitive disposition of employees due to their impairment, which has an impact on their efficiency, as their employers believe they would be unable to fulfill assigned responsibilities effectively.
A stakeholder said he once recommended an individual with intellectual disability for a job but was told: “Do you think I have the time to babysit anyone in this organisation? How do you expect me to [be] such a person?” (Non-profit organisation). This employer went on to tell the stakeholder: “You are the one that sees them as abled person but as for me I won’ t want to try them on anything than just let them depend on their family members for financial support” (Non-profit organisation).
Participants with intellectual disability noted they were usually not appreciated by employers and co-workers in most of the places they had worked. This affected their willingness to work with others or reduced their zeal for work.
For example, one participant said she offered to assist a coworker, asking if she could help get her lunch. The response of the coworker was: “I don’t want you to waste my money. Please mind your business” (Person with intellectual disability).
Another person said her colleague did not treat her with courtesy, and this resulted in misunderstanding in the workplace. At the end of the day, she was asked to leave the job. “He said he felt so bad, because the fault wasn’t his, but with his condition what could he do in such a situation?” (Person with intellectual disability).
A stakeholder said she assisted a person with intellectual disability to get a job on the understanding that he would serve as a salesman but was surprised when the boy was made to clean the house of the owner of the business instead.
The stakeholder tried to find out the reason for the change but was told: “He should count himself lucky that I allowed him into my house to clean and if not, I can send him away. Moreover, do you expect such a person to attend to my customer?” (Decision and policy marker).
Working environment: Culture to accommodation, understanding, strengths
One of the reasons employers have a negative attitude toward this category of people, according to stakeholders, is the cost of accommodation for people with intellectual disability. Not having suitable accommodation at their workplace is a barrier to people with intellectual disability. Furthermore, the participants stated that most employers assumed that hiring people with intellectual disability would raise production costs while decreasing productivity.
For example, one of the participants stated that: “The employer of an organisation told her that ‘I don’t see how I will accommodate you with others in this organisation since you find it difficult to walk straight.’ When I tried explaining that the way ‘I walk will not affect my output,’ he said that ‘It is my business’ and that he will rather give me a token than employ me to work in the organisation” (Persons with intellectual disability).
Tables 2 and 3, the results indicated that discrimination with 89 (62.2%) and x = 4.53 was ranked 1st as the most likely caused barrier to employment to people with intellectual disability while stigmatization and working environment were ranked 2nd and 3rd respectively.
Mean scores of barriers to employment of people with disabilities
Mean scores of barriers to employment of people with disabilities
Frequency and percentage of barriers to employment of people with disabilities
This study sheds light on the challenges that people with intellectual disability face when looking for and retaining employment. The use of qualitative approaches for data collection were effective in identifying and prioritizing barriers to employment for people with intellectual disability. The analysis shows that barriers to finding work by people with intellectual disability include discrimination, stigma, employers’ attitude, and management style, feeling unappreciated, and working environment. The findings are consistent with previous research on the importance and value of work for people with intellectual disability from the perspective of both emancipation [62] and quality of life [63]. The presence of disabilities, such as intellectual disability, increases the risk of unemployment [64], due to discrimination that may prevent them from being hired and denying workplace accommodations [65]. Finding shows that employment barriers were not primarily influenced by employer attitudes.
However, there is possibility that employer attitudes may differ between countries due to the local environment and context of the country. Employers in Beijing were less likely than those from Chicago and Hong Kong to endorse hiring people with disability, according to a trans-national study [66]. Although, individuals with intellectual disability face significant barriers to employment due to attitudes of discrimination and stigma at work. As a result of stakeholder and people with intellectual disability’ experiences, identified barriers to employment were ranked. The findings also revealed that people with intellectual disability and stakeholders identify stigmatisation as a barrier to employment. They are stigmatised because they are considered as less qualified and unable to work due to an absence of professional competence [67, 68]. The current findings are also consistent with reports claiming that stigma and employers’ negative attitudes towards people with disabilities are significant barriers to employment [18].
Previous research found that employers and human resource professionals reported that hiring of people with disabilities varied depending on the type of industry, the size of the organization, and management’s prior experience with people with disabilities [18, 70]. This could explain why people with intellectual disability are frequently subjected to stigmatization and hazardous working conditions in the workplace. Furthermore, the type of disability has a strong influence on employment prospects [71]. The chances of being employed are lower for people with disabilities and mental illnesses, including cerebral palsy and cerebral palsy with intellectual disability, and chronic health conditions like epilepsy [72, 73]. It seems, however, that the stigmatization experienced by people with intellectual disability impedes their active participation in the workplace, thus limiting their ability to contribute to the organization and triggering a variety of feelings and reactions on their part.
Individuals with intellectual disability’s strong work ethic and ability to adapt their behavior may also have been related to stigma, such as their desire to please others and this may have served to feel accepted or liked by others [74]. This have been the case when one of the persons with intellectual disability said, “he felt so bad”, when he was told to leave the organization where he was working because the fault wasn’t his, but with his condition what could he do in such a situation?” According to the findings, one of the barriers to employment for people with intellectual disability is the working environment. This is consistent with previous research submissions. The workplace environment has been heavily criticised for isolating people with disabilities from other members of their community, and for paying wages far below the minimum wage [32].
Furthermore, social barriers exist, as employers continue to regard people with disabilities as unfit and incapable of doing the job [42, 75]. This can also be observed in the statement of one stakeholder who noted that an individual with intellectual disability was told that “He should count himself lucky that I allowed him into my house to clean and if not, I can send him away.” The reason for such statement is because people with intellectual disability are viewed by the general population as a subordinate group, which can include both positive stereotyping, such as “warm” (likable) and negative stereotyping, such as “incompetent,” resulting in feelings of sympathy for them [76, 77]. Therefore, to support themselves, they must rely on the generosity of friends, family, and charitable organizations [39]. It is appropriate to note that taking steps to remove these barriers must address the negative mindset of potential employers. Even in high-income countries, employers are skeptical about people with disabilities as dependable and productive workers [66].
Conclusion
The findings of this study have contributed to a better understanding of the severity of the systemic barriers which people with intellectual disability may face while looking for paid jobs. Researchers have gained valuable insight into the experiences of people with intellectual disability in the competitive job market because of this study. Moreover, the findings revealed that individuals with disabilities are actively engaged in job search activities, and successfully negotiate obstacles at work, despite the barriers identified by study participants. Improving job opportunities for people with intellectual disability would necessitate a multi-pronged strategy, however, the study’s strength lies in its understanding that progress can only occur if jobs for people with intellectual disability are promoted on several fronts, with a cohesive and coherent plan and message. Efforts to improve the self-advocacy of people with intellectual disability, assist their family members in job search efforts, and educate coworkers and managers, are vital in realigning the future of people with intellectual disability. Considering the study’s limitations, its findings should be interpreted cautiously. The study examined the barriers to employment of individuals with mild intellectual disability or borderline functioning who have good verbal communication skills. The study did not consider individuals with severe disabilities and poor verbal communication who may have unique work experiences. Finally, people with intellectual disability need more opportunities to cultivate healthy coping strategies and strengthen their work-related self-efficacy.
Funding
This work was supported by the South African Research Chairs Initiative of the Department of Science and Innovation and National Research Foundation of South Africa (grant number: 87300, 2017).
Conflict of interest
The authors confirm that there is no conflict of interest with respect to the data presented in this paper.
Data availability
The data presented in this study are available upon reasonable request from the corresponding author.