Article summary

NEW RESEARCH

Developmental Trajectories in Adolescents and Adults With Autism:

The Case of Daily Living Skills Leann E. Smith, Ph.D., Matthew J. Maenner, Ph.D., Marsha Mailick Seltzer, Ph.D.

Objective: This study aimed to investigate the longitudinal course of daily living skills in a large, community-based sample of adolescents and adults with autism spectrum disorders (ASD) over a 10-year period. Method: Adolescents and adults with ASD (n � 397) were drawn from an ongoing, longitudinal study of individuals with ASD and their families. A comparison group of 167 individuals with Down syndrome (DS) were drawn from a linked longitudinal study. The Waisman Activities of Daily Living Scale was administered four times over a 10-year period. Results: We used latent growth curve modeling to examine change in daily living skills. Daily living skills improved for the individuals with ASD during adolescence and their early 20s, but plateaued during their late 20s. Having an intellectual disability was associated with lower initial levels of daily living skills and a slower change over time. Individuals with DS likewise gained daily living skills over time, but there was no significant curvature in the change. Conclusions: Future research should explore what environmental factors and interventions may be associated with continued gains in daily living skills for adults with ASD. J. Am. Acad. Child Adolesc. Psychiatry, 2012;51(6): 622– 631. Key Words: daily living skills, autism, adolescence, adulthood, trajectories

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A utism spectrum disorders (ASDs) are life-long developmental disabilities that af-fect an estimated 1 in 110 children in the United States.1 ASDs are characterized by im- pairments in communication and social interac- tion as well as the presence of repetitive behav- iors. In recent years, increasing attention has been given to understanding the behavioral phe- notype of ASD during adolescence and adult- hood. For instance, researchers have explored how autism symptoms and behavior problems change across adolescence and adulthood.2-4

Other work has focused on measuring educa- tional and occupational outcomes for adults with ASD, with results indicating that few individuals reach high levels of independence.5,6 Virtually no studies, however, have explored the develop- ment of independence in daily living skills in adolescents and adults with ASD, even though such abilities are often cited as important factors

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for successful outcomes for adults with intellec- tual and developmental disabilities (IDD).7,8 The

resent study addressed this gap by examining rajectories of daily living skills over a 10-year eriod in a large, community sample of adoles- ents and adults with ASD.

aily Living Skills in Individuals With ASD aily living skills constitute a critical domain of

daptive behaviors, which are defined as behav- ors necessary for age-appropriate, independent unctioning in social, communication, daily liv- ng, or motor areas. Past research suggests that he development of daily living skills may be articularly challenging for individuals with SD. Children with autism often have significant

mpairments in daily living skills compared with ell-matched controls,9,10 and as early as 36

months of age such children display a greater discrepancy between their adaptive behavior and mental age than children with other develop- mental delays.11 These delays in daily living kills may become more pronounced over time.

n a validation study of the Vineland Adaptive

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Behavior Scales’ supplemental norms for autism, younger children with ASD had higher standard scores than older children with ASD in all adap- tive behavior domains, including daily living skills, suggesting that as children with ASD grow, they increasingly lag behind their same- age peers.12 Similarly, in sample of 1,089 children and adolescents with ASD, Kanne et al.13 recently found that adolescents had a greater gap be- tween their mental age and adaptive skills than younger children, suggesting that individuals with ASD may gain daily living skills at a pace slower than the rate of their intellectual growth. These cross-sectional findings highlight the need for longitudinal studies to elucidate how daily living skills change over time for individuals with ASD and what factors are associated with improvements in these skills.

Most studies that have examined within-person change in daily living skills for individuals with autism notably have focused on early childhood. For instance, Freeman et al.14 explored change in the Vineland Adaptive Behavior Scales in chil- dren with ASD and found that daily living skills improved with age. In addition, results indicated that children with IQs at or above 70 improved at a faster rate than children whose IQs were below 70.14 Similarly, in a longitudinal study of daily living skills in preschoolers with ASD, Green and Carter15 found a linear increase in daily living skills over a 3-year period, with lower IQ scores and higher levels of autism symptoms associated with slower gains. In a recent study of children with high-functioning autism, daily living skills improved over time, although the rate of change slowed as children entered adolescence.16 Taken together, these studies suggest that daily living skills improve during early childhood and into adolescence, although the rate of change slows over time, and that the presence of an intellectual disability (ID) further slows the rate of growth. Questions remain, however, regarding whether daily living skills continue to improve through ado- lescence and adulthood and the extent to which ID may influence these later-life trajectories.

The literature on daily living skills for adults with other types of IDD may offer insights into possible patterns of change in daily living skills for those with ASD. For example, Esbensen et al.17 explored functional abilities (housekeeping, personal care, meal-related activities, and mobil- ity domains) over a nine-year period in a sample

of individuals with IDD, including a large sub-

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sample of individuals with Down syndrome (DS). Results indicated that housekeeping skills improved over time, whereas personal care and mobility skills declined over the same period. Improvements in housekeeping skills were fast- est for younger individuals and declines in per- sonal care skills were fastest for older individu- als.17 However, this study did not examine the

ossibility of curvilinear change. It may be that aily living skills improve for individuals with

DD during adolescence and early adulthood but ecline later in adulthood. The present study xamined this hypothesis by using latent growth urve modeling to test for linear and curvilinear hange in daily living skills for adolescents and dults with ASD as well as for similarly aged ndividuals with DS.

resent Study he primary aim of the present study was to

nvestigate the longitudinal course of daily living kills in a large, community sample of adoles- ents and adults with ASD. Daily living skills ere measured on four occasions over a 10-year eriod, allowing for an examination of linear and urvilinear change. Furthermore, due to the wide ange of ages of participants in our study (10 –52 ears at Time 1), we were able to explore the ffects of the age of the individual with ASD termed “child age”) in addition to ID status on nitial level of daily living skills as well as change n daily living skills over time. Residential status f the individual with ASD (living with parent s. not living with parent) also was examined as time-varying covariate. To provide a bench- ark for interpreting trends among the adoles-

ents and adults with ASD, a secondary aim of he present study was to examine change in daily iving skills among similarly aged individuals

ith DS, again measured on four occasions over 10-year period. Although we did not conduct a irect comparison given differences in the age etween samples, we explored change in the DS ample to provide additional context for inter- reting scores in the ASD group.

Based on past studies documenting that au- ism symptoms and behavior problems tend to ecome less severe during adolescence and dulthood,2 we hypothesized that there would e concomitant improvements in daily living kills over the course of the study. However, ased on recent work by Taylor and Seltzer3

indicating that the rate of improvement in autism

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symptoms and behavior problems slows after entering adulthood, we also hypothesized that the change in daily living skills would be curvi- linear; that is, that the rate of change would decrease over time. Next, consistent with past studies showing that daily living skills improve with age for children with ASD,14,15 we hypoth- esized that there would be a significant associa- tion between age and initial level of daily living skills. Given the association between intelligence and daily living skills in other samples,10,13,18 we hypothesized that having an ID would be associ- ated with a lower initial level of daily living skills. Based on the association between ID and growth in daily living skills in studies of younger children with ASD,14,15 we hypothesized that having an ID would be associated with slower change in daily living skills for adolescents and adults with ASD.

Regarding our secondary aim, based on past work showing gains over time in functional abilities for individuals with ID,17 we hypothe- sized that there would be improvements in daily living skills for individuals with DS. We also hypothesized that individuals with DS would dis- play curvilinear change, or a slowing of improve- ment, consistent with findings that individuals with DS are at risk for dementia as they age.19,20

METHOD Autism Sample Participants Participants were drawn an ongoing, multi-wave, lon- gitudinal study of 406 individuals with ASD and their families, the Adolescents and Adults with Autism study (AAA).21 The present study focused on four of eight points of data collection, Times 1, 4, 7, and 8. Families were recruited via agencies, schools, diagnos- tic clinics, and media announcements. At entry into the AAA study, families met three criteria: the family included a child 10 years of age or older; the child had received a diagnosis of ASD from a medical, psycho- logical, or educational professional; and scores on the Autism Diagnostic Interview—Revised (ADI-R)22

were consistent with the parental report of an ASD. Of the original sample of 406 individuals, nine

were excluded from the present study, as they did not have complete data on activities of daily living at Time 1. Excluded cases were not significantly differ- ent from the full sample in child age, sex, family income, or parental education. The individuals with ASD in the present study ranged from 10 to 52 years of age at the beginning of the study (Time 1: mean � 21.84 years, SD � 9.32 years; Time 4: mean � 26.25 years, SD � 9.36 years; Time 7: mean � 29.87 years, SD � 9.19

years; and Time 8: mean � 31.23 years, SD � 9.02). The

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ajority of the sample was male (73%) and 70% of the ample had a comorbid diagnosis of ID.

When the AAA study began in 1998, 65% of the ndividuals with ASD lived with their families and 5% lived away from home. An increasing proportion f individuals moved away from the family home at ach subsequent point of data collection, such that at imes 4, 7, and 8, 56%, 45%, and 47% were co-residing ith their families, respectively. About half (52.2%) of arent respondents had at least a bachelor’s degree, nd the median annual household income was $50,000 o $59,000 in 1998 to 1999. The majority of participants 93%) were white. Most respondents were mothers 96.5%), with 14 fathers participating (3.5%).

There were no significant differences between fami- ies who participated in all waves of data collection and amilies with missing data in child sex or ID status. owever, consistent with age-related morbidity and ortality, families of older individuals were more likely

o end study participation than were their younger ounterparts (F � 3.78, p � .05). Importantly, there were

no significant associations between complete study par- ticipation and daily living skill scores at Time 1.

Down Syndrome Sample Participants To benchmark changes in daily living skills in individ- uals with ASD, a sample of individuals with DS was drawn from a linked longitudinal study of 461 indi- viduals with ID.23 Families were included in the study f they met two criteria: the mother was between 55 nd 85 years of age and the son or daughter lived at ome with her. Of the 461 target children in the study, 69 of the sons or daughters had a diagnosis of DS. Of hese cases, 2 were excluded from the present study as hey had missing data on activities of daily living at Time . The individuals with DS in the present study ranged rom 15 to 56 years of age at Time 1 (mean � 31.61 years, D � 7.19 years). The majority were daughters (60.5%), nd 28.8% of mothers had at least a bachelor’s degree. he majority of participants (92%) were white.

When this longitudinal study began, all of the ndividuals with DS lived at home with their families.

owever, some individuals changed residences at ach subsequent point in data collection, such that at imes 4, 7, and 8, 94%, 81%, and 92% were co-residing ith their families, respectively. Families who partici- ated in all waves of data collection were not signifi- antly different from families with missing data on child ex, but families of older individuals were more likely to nd study participation than families of younger individ- als (F � 6.94, p � .05). As with the ASD sample, there as no association between complete study participation

nd Time 1 daily living skills scores.

Procedure and Measures Procedures and measures were identical for both the

ASD and DS samples. At each time point (Times 1, 4,

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7, and 8), mothers completed self-administered ques- tionnaires and participated in a 2- to 3-hour in-home interview. For the ASD sample, data collection be- tween Times 1 and 4 occurred an average of 5.00 years apart. Approximately 3.45 years occurred between Times 4 and 7, and 1.99 years occurred between Times 7 and 8. For the DS sample, an average of 4.44 years elapsed between Times 1 and 4, 4.47 years between Times 4 and 7, and 1.72 years between Times 7 and 8.

Independence in activities of daily living was mea- sured using the Waisman Activities of Daily Living Scale (W-ADL; Maenner, Smith, Hong, Makuch, Greenberg, and Seltzer, unpublished data, 2011) (Table 1). Parent respondents rated their son or daughter’s level of independence on 17 items covering the do- mains of personal care, housekeeping, and meal- related activities. Each item was rated on a three-point scale of independence 0 (does not perform the task at all), 1 (performs the task with help), or 2 (performs the task independently); and items were summed. Coeffi-

TABLE 1 Waisman Activities of Daily Living Scale

1. Making his/her own bed 2. Doing household tasks, including picking up around the

house, putting things away, light housecleaning, etc. 3. Doing errands, including shopping in stores 4. Doing home repairs, including simple repairs around

the house, non-technical in nature; for example, changing light bulbs or repairing a loose screw

5. Doing laundry, washing and drying 6. Washing/bathing 7. Grooming, brushing teeth, combing and/or brushing

hair 8. Dressing and undressing 9. Toileting

10. Preparing simple foods requiring no mixing or cooking, including sandwiches, cold cereal, etc.

11. Mixing and cooking simple foods, fry eggs, make pancakes, heat food in microwave, etc.

12. Preparing complete meal 13. Setting and clearing table 14. Drinking from a cup 15. Eating from a plate 16. Washing dishes (including using a dishwasher) 17. Banking and managing daily finances, including

keeping track of cash, checking account, paying bills, etc. (Note: if he/she can do a portion but not all circle ‘1’ with help.)

Note: Instructions that accompanied the items: “Next we would like to know about your son or daughter’s current level of independence in performing activities of daily living. For each activity please tell me the number which best describes your son/daughter’s ability to do the task. For example, Independent would mean your son/daughter is able to do the task without any help or assistance.” 2 � independent or does on own; 1 � does with help; 0 � does not

do at all.

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cient � values for the total score in the ASD sample ranged from 0.90 to 0.94 for Times 1, 4, 7, and 8; for the DS sample, the � values ranged from 0.91 to 0.93.

Child characteristics of age (continuous) and ID status (1 � yes, 0 � no) were included as predictors of

aily living skills scores in the ASD sample analyses. rocedures for assessing the presence of ID in our ample have been reported in detail in previous stud- es24 and involved a clinical consensus process using nformation drawn from sources including direct cog- itive testing and educational records. Residential sta-

us (0 � co-residing with parent, 1 � not co-residing ith parent) was also included as a time-varying

ovariate.

Data Analysis To address our primary aim, we used latent growth curve (LGC) modeling to examine daily living skills over a 10-year period. LGC modeling integrates indi- vidual growth modeling (i.e., hierarchical linear mod- eling) and structural equation modeling (SEM) ap- proaches25 and provides estimates of mean structure intercept and slope), reflecting the average starting oint for all individuals and average rate of change.26

It is also possible to model nonlinear change; by adding a quadratic parameter to a model that already includes an intercept and linear slope, the growth trajectory becomes curvilinear. In a purely linear model, the rate of change is presumed to be constant over time; in contrast, a quadratic latent curve model allows the rate of change either to increase or decrease over time. As an example, the magnitude of change in repeated measures may be larger in earlier years than in later years.26 The addition of a quadratic trend also lters the interpretation of the linear slope, such that he linear slope coefficient is changed to reflect the nstantaneous rate of change at a specific point in ime.25 If the coefficient for the quadratic factor is egative, then the trajectory is concave to the time axis. onversely, the presence of a positive quadratic trend

ndicates that the trajectory is convex to the time axis.25

After preliminary analyses of variance confirmed the presence of change over time in daily living skills without controlling for age and ID status, a multivar- iate LCG model was assessed in which age and ID status were included as time-invariant predictors and residential status was included as a time-varying co- variate. To address our secondary aim of providing an illustrative benchmark for interpreting the patterns of daily living skills observed in our ASD sample, we used LGC modeling to assess change in daily living skills in a sample of individuals with DS over a similar period of time. All models were evaluated in terms of measures of goodness-of-fit using the Mplus modeling program.27 A satisfactory fit is indicated by a compar- ative fit index (CFI) close to one and a root mean square error of approximation (RMSEA) less than or

equal to 0.08.

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SMITH et al.

RESULTS Primary Aim: Daily Living Skills in Adolescents and Adults With ASD Activities of daily living were assessed at 4 time points (Times 1, 4, 7, and 8) in the ASD sample. We present means, standard deviations, ranges, and intercorrelations among study variables in Table 2. Figure 1 depicts a mixed-effects regres- sion model showing individual scores by age and intellectual disability status. By the end of the study, the average score for the group was 20.59 (SD � 8.08) on a scale in which a score of 34 reflects complete independence. Only 16.5% of the sample had scores of 30 or above at Time 8. Scores at each time point were significantly cor- related with scores at all other time points.

We evaluated an LGC model of daily living skills that specified quadratic growth over time and included age and ID status as predictors of all latent factors. Residential status (co-residing vs not co-residing) also was included as a time- varying covariate (Figure 2). In this model, the latent intercept, linear slope, and quadratic trend were indicated by daily living scores at Times 1, 4, 7, and 8. The factor loadings for the intercept factor were all set to 1. The loadings for the linear slope factor were fixed at 0, 5.0, 8.45, and 10.44, reflecting the average length of time between waves of data collection. The loadings for the quadratic slope factor were the linear values squared.

This model displayed excellent fit [�2 (15, n � 406)� 12.69, p � .63; RMSEA� 0.00; CFI � 1.0]. There was a significant positive linear slope (est. � 1.25, SE� 0.19, p�.001) and a significant negative quadratic trend (est.� �0.07, SE� 0.02, p � .001). However, the linear trend in a model that in- cludes a quadratic trend is interpreted as the instantaneous rate of change. This means that for different snapshots of time, the rate of change may be different. As such, to determine how daily living skills were changing across time, we also examined the values for the linear slope when time was centered at Times 4, 7, and 8, respectively. At Time 4, the linear trend was positive (est.� 0.56, SE� 0.07, p�.001), but at Time 7 the linear trend was nonsignificant (est. � 0.07, SE �0.15, p � .57). At Time 8, however, there was a significant negative linear trend (est.� �0.89, SE� 0.27, p � .001). Taken together, these findings suggest that, on average, scores were increasing at Times 1 and 4 but were no

longer significantly changing at Time 7. By Time

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TA

T T T T C ID M R N *

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8, scores were beginning to decrease. In other words, daily living skills were improving during adolescence and the early 20s, plateaued around the time of the late 20s, and started to decline during the early 30s. However, we encourage some caution in interpreting the exact nature of change for older individuals, as the majority of the sample was under the age of 30 at the end of the study.

There also were significant relationships be- tween age, ID status, and the latent factors. Age was positively associated with the intercept of daily living skills, with older individuals having higher scores at the start of the study (��0.24, p � .001). Age also was associated with the linear factor (� � �0.31, p � .01) and the quadratic factor (� � 0.22, p � .10), although this associa- tion with the quadratic factor was not significant at the .05 level. These age effects suggest that older individuals displayed a faster rate of cur- vature; that is, they were declining at a faster

FIGURE 1 Change in Waisman Activities of Daily Livin sample, individual and group trajectories. Note: Quadrat

rate. In addition, ID status was a significant s

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predictor of the intercept of daily living skills, with individuals with ID having lower initial levels of daily living skills at the start of the study (�� �0.52, p � .001). Having an ID was also

egatively associated with the linear factor (� � �0.20, p � .01), suggesting that individuals with D were gaining skills at a slower rate than ndividuals without ID. Residential status was a tatistically significant covariate of daily living kills at Times 1 and 8, with coresidence between arent and child associated with lower scores.

econdary Aim: Daily Living Skills in Individuals ith Down Syndrome

o explore trajectories of daily living skills in the S sample, daily living skills were assessed at

our time points (Times 1, 4, 7, and 8). We present eans, standard deviations, ranges, and intercor-

elations among study variables in Table 3. Fig- re 3 depicts a mixed-effects regression model

-ADL) scores over time for autism spectrum disorder ge2) mixed-model paramaterizations displayed.

g (W ic (a

howing individual scores by age. By the end of

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SMITH et al.

the study, the average score for the group was 23.83 (SD � 6.33) on a scale in which a score of 34 reflects complete independence. Only 19.6% of the sample had scores of 30 or above at Time 8. Scores at each time point were significantly cor- related with scores at all other time points.

FIGURE 2 Latent growth curve model of Waisman Activities of Daily Living (ADL) scores for individuals with autism spectrum disorders (N � 397). Note: ID � intellectual disability. *p � .05, ��p � .01, ���p � .001, †p � .10.

TABLE 3 Descriptive Statistics and Intercorrelations Amo

Time 1 W-ADL Time 4 W-ADL

Time 1 W-ADL 1 (n � 166) Time 4 W-ADL 0.88*** (n � 124) 1 (n � 125) Time 7 W-ADL 0.83*** (n � 98) 0.88*** (n � 92 Time 8 W-ADL 0.85*** (n � 66) 0.86*** (n � 63 Child age 0.12 (n � 166) 0.03 (n � 125) Mean (SD) 22.55 (6.37) 23.69 (6.56) Range 3–33 2–33

Note: W-ADL � Waisman Activities of Daily Living.

***p � .001.

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We evaluated a LGC model of daily living skills that specified linear and quadratic growth over time and included age as a predictor of all latent factors and residential status included as a time-varying covariate. Since all individuals in the DS sample had a diagnosis of ID, disability status was not included in this model. In this model, the latent intercept and linear slope were indicated by daily living scores at Times 1, 4, 7, and 8. The factor loadings for the intercept factor were all set to 1. The loadings for the linear slope factor were fixed at 0, 4.44, 8.91, and 10.63, reflecting the average length of time between waves of data collection. The loadings for the quadratic slope factor were the linear values squared.

This model displayed good fit (�2 (11, N � 67) � 16.84, p � .11; RMSEA � 0.06; CFI � 0.99). here was a positive linear slope (est.� 0.86, E � 0.45), indicating improvement in daily iving skills over time, although this effect only pproached statistical significance (p � .058). mportantly, the average increase of 0.86 point er year is a clinically significant change. The uadratic slope factor was nonsignificant (est.� 0.04, SE � 0.04, p � .42), indicating that there as no curvature in the change in daily living

kills over time. There was a trend for age to be ositively associated with the intercept of daily

iving skills (p � .10). There were no significant ssociations between age and the other latent actors. Residential status was not a significant ovariate at any of the time points.

DISCUSSION The present study used LGC modeling to inves- tigate trajectories of daily living skills for ado- lescents and adults with ASD. Past research

tudy Variables for Down Syndrome Sample

Time 7 W-ADL Time 8 W-ADL Child Age

(n � 99) 0.92*** (n � 60) 1 (n � 66)

�0.02 (n � 99) 0.01 (n � 66) 1 (n � 167) 23.37 (7.41) 23.83 (6.33) 31.61 (7.19) 1–32 5–33 15–56

ng S

) )

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t t A i s T l i b e o l t

DEVELOPMENTAL TRAJECTORIES AND AUTISM

Downloa

examined trajectories of daily living skills for individuals with ASD during childhood and early adolescence but not across adolescence and adulthood. In contrast, the present study in- cluded a large, community-based sample of indi- viduals with ASD with a wide age range (10 –52 years), which enabled us to examine the influ- ence of age as well as ID status on change in daily living skills well into adulthood. The longitudi- nal design of the current study addressed an- other gap in the literature by allowing for an examination of curvilinear change over a 10-year period. Finally, the present study included an additional analysis of trajectories of daily living skills in a linked longitudinal study of individu- als with DS, providing a unique opportunity to understand patterns of change in two different groups of individuals with IDD.

Most notably, the present study found signif- icant quadratic change in daily living skills for

FIGURE 3 Change in Waisman Activities of Daily Livin individual and group trajectories. Note: Linear mixed–mo

individuals with ASD, indicating that skills im- o

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proved during adolescence and the early 20s, plateaued around the late 20s, and began to decline in the early 30s. This is consistent with our hypothesis that there would be improve- ments in skills for individuals with ASD but that the rate of change would slow as individuals aged. Recently, Taylor and Seltzer3 documented hat the rate of improvement in autism symp- oms and behavior problems for adolescents with SD slowed down (or even stopped) after the

ndividuals with ASD exited the secondary chool system (typically during the early 20s). aken together, these findings suggest that ado-

escence is a time of growth and improvement for ndividuals with ASD in a variety of domains, ut that, on average, the period of improvement nds by the time such individuals reach 30 years f age. The slowing of improvement in daily

iving skills is particularly concerning given that he plateau in gains was not due to ceiling effects

-ADL) scores over time for Down syndrome sample; aramaterization displayed.

g (W del p

r a mastery of skills (Maenner et al., unpub-

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l o o n s l l o w e c w i b m s

SMITH et al.

lished data, 2011). In fact, by the end of the study period, on average, the individuals with ASD were failing to perform more than one-third of the measured daily living skills independently.

Consistent with our hypothesis and with other studies demonstrating an association between age and daily skills,14,15 we found that being older at the start of the study was associated with higher levels of initial daily living skills. Findings also indicated that older individuals displayed a faster rate of curvature; that is, the older an individual was at the start of the study, the sooner he or she started to display a plateau and eventual decline in daily living skills. Also con- sistent with past studies of daily living skills in children with ASD,14,15 having an ID was associ- ated with lower initial levels of daily living skills and with slower rates of change.

A secondary aim of the present study was to examine the pattern of change in daily living skills among individuals with DS to provide a context for interpreting the pattern of change observed in our ASD sample. Past research has shown that adults with DS have higher levels of daily living skills than individuals with other intellectual disabilities,17,16 including individuals with ASD and ID.7,28 Findings from the present study indicated that individuals with DS show a different pattern of change in daily living skills, with these adults continuing to gain skills across adulthood. The slowing of improvement in daily living skills for adults with ASD may contribute to the poorer adult outcomes observed in indi- viduals with ASD compared with peers with DS who had similar levels of intellectual functioning.7

The limitations of the present study point to areas for future research. The majority of individ- uals in our sample were white and middle-class, highlighting a need to examine these skills in more diverse groups. Similarly, although we controlled for residential status, it may be that other environmental contexts (e.g., type of day activity) also influence change in daily living skills. It also is important to note that the sample size for the DS group was small for conducting growth curve analyses, which leaves the possi- bility that more nuanced patterns of change may be observed in larger groups of adults with DS. In addition, the majority of the DS sample were already adults at the start of the study, thus limiting the extent to which direct comparisons

between the two samples would be informative;

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a sharper increase in skills may have been ob- served in the DS group, had we measured these skills earlier in development. Although our ob- servation of differences between the ASD and DS groups was entirely exploratory and descriptive, it does raise an intriguing question for future investigation. Finally, the present study is limited by the use of use of a categorical variable mea- suring ID status, as IQ scores were not available for all participants.

This study has important implications for fu- ture research and clinical practice. By the end of the study period, all individuals with ASD were adults but, on average, these adults had not achieved independence in many of the daily living skills that we measured. However, as other researchers have noted,13,29 daily living skills are ess tied to the core symptoms of autism than ther aspects of functioning, such as socialization r communication, and thus may be more ame- able to change. The improvement in daily living kills for individuals with ASD into the late 20s ikewise suggests that it may be possible for daily iving skills to be gained at later points in devel- pment, even as skills in other areas plateau. It ill be critical for future research to explore what

nvironmental factors may be associated with ontinued gains of daily living skills for adults ith ASD as well as the best practices for teach-

ng these skills. Although some attention has een given to developing behavioral and phar- acological interventions to improve daily living

kills in younger children with ASD,30,31 new research is needed to develop strategies for sup- porting gains in daily living skills for individuals with ASD at later points in the life course. &

Accepted March 7, 2012.

Drs. Smith, Maenner, and Seltzer are with the Waisman Center, University of Wisconsin–Madison.

This research was supported by National Institute of Health (NIH) grants R01 AG08768 (M.M.S.), T32 HD07489 (M.M.S.), and P30 HD03352 (M.M.S.).

The authors are extremely grateful to the families who participated in this study; without their generous commitment, this research would not have been possible.

Disclosure: Drs. Smith, Maenner, and Seltzer report no biomedical financial interests or potential conflicts of interest.

Correspondence to: Leann E. Smith, Ph.D.,1500 Highland Avenue, Waisman Center, Madison, WI 53705; e-mail: lsmith@waisman. wisc.edu

0890-8567/$36.00/©2012 American Academy of Child and Adolescent Psychiatry

DOI: 10.1016/j.jaac.2012.03.001

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