Our study extended comparisons of individuals with ASD and DS into adulthood and showed that, relative to adults with DS, adults with ASD who also had ID continue to show the pattern of poorer outcomes that past research documented as evident during childhood. Although the two groups were comparable with respect to achieving vocational independence, adults with ASD and comorbid ID were living in less independent residential settings and had less contact with friends and neighbors than adults with DS, two core components of independence in adult life (Howlin et al., 2004
). Adults with ASD were also found to have lower ratings of overall independence in adult life than adults with DS. Only 37.4% of adults with ASD were rated as having a moderate or high level of independence in adult life, compared to 62.3% of adults with DS. Impairments in social and communication in adults with ASD may be contributing to their poorer outcomes in contact with friends and neighbors. However, it should be noted that adults with DS and adults with ASD were comparable in having infrequent contact with friends and neighbors. Thus, the poorer outcome on this component of independence in adult life cannot fully be accounted for by impairments associated with the core features of ASD.
In addition to having poorer overall adult outcomes as compared to adults with DS, adults with ASD were also more impaired in other variables associated with adult functioning. Adults with ASD were less able to carry out typical tasks of daily living, had poorer literacy skills, exhibited more behavior problems, received fewer services, and had more unmet service needs than adults with DS, even when level of ID was controlled. Our results suggest that the gap between individuals with ASD and DS observed in childhood does not narrow with age, but it instead persists into adulthood, and that the pattern of behavior problem and symptom abatement observed in adults with ASD (Shattuck et al., 2007
) is not so prominent as to overcome existing group differences with adults with DS.
There were clear differences between the “average” adult with ASD and the “average” adult with DS in our sample. The average adult with ASD lived in a community residence, visited with friends less frequently than once a month (i.e., about one to ten times per year), and participated in a sheltered workshop or a day habilitation program. He or she was in good health, needed assistance to do most activities of daily living, was able to read and write only a few words, and exhibited at least three different types of problem behaviors (most commonly an unusual habit, withdrawn behaviors, and self-injurious behaviors). This average individual with ASD received more than three services (most frequently income support, psychological or psychiatric services, and transportation services) and had one unmet service need.
In comparison, the average adult with DS lived at home with his or her parents, visited with friends about once a month, and worked in a sheltered workshop, a profile consistent with the findings of other studies (Carr, 2008
). He or she was in good to excellent health, was independent or needed only partial assistance on most daily living tasks, was able to read and write a few words or sentences, and exhibited only one type of problem behavior (most commonly an unusual habit). This average adult with DS received more than three services (most frequently income support, vocational services, and agency sponsored recreational or social activities) and had less than one unmet service need.
Although adults with DS have fewer impairments than adults with ASD, it should be noted that they still have some limitations. No individual with DS met the criteria for a very high level of independence in adult life, namely living independently, seeing their friends several times a week and working in competitive employment. Furthermore, about a third of the adults with DS never visited with friends or did so only once in the past year, and 15% had no vocational activity.
Our findings also indicate that the factors that are associated with independence in adult life in individuals with DS differ from those are associated with independence among individuals with ASD. Functional abilities were related to better outcomes for both adults with ASD and DS, whereas receiving more services (speech and language, recreational, transportation) were related to better outcomes only for adults with DS. This difference is noteworthy, as adults with ASD were less likely to receive recreational services, and more likely to be in need of recreational services and speech and language therapy compared to adults with DS.
Another predictor of overall independence among adults with ASD was not
receiving psychological or psychiatric services. Our findings suggest that adults with ASD not receiving psychological or psychiatric services are more likely to have better adult outcomes. Comorbidity of psychological disorders among individuals with ASD has been a relatively under-studied area until recently (Tsakanikos, Costello, Holt, Bouras, Sturmey & Newton, 2006
). Early indications suggest that the prevalence of psychopathology among adults with ASD is no different from their peers with ID (Melville et al., 2008
; Tsakanikos et al., 2006
), yet over 60% of adults with ASD in our sample were receiving psychological or psychiatric services (versus 19% of adults with DS). It will be important for future research to examine the best ways to assess psychological and psychiatric needs among adults with ASD so that appropriate interventions can be put in place. Identifying the presence of comorbid behavior problems or psychological disorders in adolescents and young adults with ASD prior to exiting the school system and leaving the family home may be the best way to target services to this population and to minimize the long-term impact of these disorders on overall independence in adult life.
It was surprising that behavior problems did not emerge as a significant predictor of independence in adult life in our model. In examining this finding in more detail, we found that behavior problems were inversely correlated with residential independence, vocational independence and overall independence in adult life on a bivariate level (r = -.18, -.23, -.28 respectively, all p < .05). However, in the regression model, behavior problems did not predict independence in adult life beyond functional abilities and service use. This suggests that for both adults with ASD and DS, adaptive behaviors may be more strongly related to independence in adult life than maladaptive behaviors. However, this finding warrants replication in future research and thus should be interpreted cautiously.
A major strength of this study is that we were able to assess the lives of adults with ASD in comparison to a group of individuals with another type of developmental disability. In addition to the difference in diagnostic status, however, there were also other differences between our samples that resulted from the fact that they were initially recruited to participate in different studies. All of the individuals with DS were required to be co-residing with their families at the time that the study began, which could have contributed to some of the differences seen between the groups. Indeed, adults who lived with their families were more likely to be in need of services and receive fewer services than adults living in community residences. Although we controlled for residential status whenever possible, we were not able to do so in the independence in adult life analyses, since one of the components of independence in adult life was residential status. Similarly, due to non-independence, we were unable to account for the complex relationship between services received and unmet need for services in predicting adult outcomes, as questions about unmet needs are asked only when the particular service was not received. Other sample limitations included the fact that most of the families were Caucasian and that they all volunteered to participate. Thus, these families may not be entirely representative of other families with adult children with ASD or DS. Furthermore, because all of the adults with ASD also had ID, these findings may not be fully applicable to adults with ASD with average intelligence. Finally, although we controlled for level of ID, the fact that adults with ASD had lower levels of ID may have contributed to their poorer outcomes in unknown ways.
Even in comparison to adults with significant disabilities, the life skills of adults with ASD are severely lacking. A primary goal of service provision efforts should be to elevate the skills and activities of adults with ASD to be more commensurate with those of adults with other types of developmental disabilities. While a person's level of cognitive ability may be less malleable, especially in adulthood, it is certainly within our grasp as service providers to try to improve a person's level of functional abilities. Greater deficits in functional abilities, which are first apparent in comparative studies of children with ASD, may have cumulative effects over the life-course that ultimately limit the independence of adults with ASD. Additionally, ASD-related social and communication impairments may impact relative rates of functional skill acquisition and negatively influence the trajectory of skill development in individuals with ASD. Investigations are needed to determine why children and adults with ASD do not appear to benefit from the same services as individuals with non-ASD developmental disabilities so that new, more effective methods of service delivery can be developed for them.