Abstract
Objective
Pediatric traumatic brain injury (TBI) may affect children’s ability to perform everyday tasks (i.e., adaptive functioning). Guided by the American Association for Intellectual and Developmental Disabilities (AAIDD) model, we explored the association between TBI and adaptive functioning at increasing levels of specificity (global, AAIDD domains, and subscales). We also examined the contributions of executive function and processing speed as mediators of TBI’s effects on adaptive functioning.
Method
Children (ages 8–13) with severe TBI (STBI; n=19), mild-moderate TBI (MTBI; n=50), or orthopedic injury (OI; n=60) completed measures of executive function (TEA-Ch) and processing speed (WISC-IV) an average of 2.7 years post-injury (SD = 1.2; range: 1–5.3). Parents rated children’s adaptive functioning (ABAS-II, BASC-2, CASP).
Results
STBI had lower global adaptive functioning (η2 = .04–.08) than the MTBI and OI groups, which typically did not differ. Deficits in the STBI group were particularly evident in the social domain, with specific deficits in social participation, leisure, and social adjustment (η2 = .06–.09). Jointly, executive function and processing speed were mediators of STBI’s effects on global adaptive functioning and in conceptual and social domains. In the STBI group, executive function mediated social functioning, and processing speed mediated social participation.
Conclusions
Children with STBI experience deficits in adaptive functioning, particularly in social adjustment, with less pronounced deficits in conceptual and practical skills. Executive function and processing speed may mediate the effects of STBI on adaptive functioning. Targeting adaptive functioning and associated cognitive deficits for intervention may enhance quality of life for pediatric TBI survivors.
Keywords: pediatrics, traumatic brain injury, adaptive functioning
Each year in the United States, over half a million children under 15 years of age sustain a traumatic brain injury (TBI), constituting a prominent public health concern (Faul, Xu, Wald, & Coronado, 2010). TBI can cause disruptive and lasting deficits across several areas of functioning, including physical, emotional, social, and cognitive domains (Beauchamp & Anderson, 2010). Furthermore, children with TBI, particularly those with a severe TBI, experience difficulty with adaptive functioning (Catroppa, Anderson, Morse, Haritou, & Rosenfeld, 2008; Max et al., 1998; Taylor et al., 2002). According to the American Association on Intellectual and Developmental Disabilities (AAIDD), adaptive functioning reflects competence in three domains: conceptual (e.g., language and literacy), practical (e.g., self-care, following directions, crossing the street safely, taking medications), and social (e.g., interpersonal skills, social problem solving; Schalock et al., 2010). To more comprehensively understand how children with TBI adapt to their environment, the current study explored adaptive functioning after pediatric TBI in depth and how cognitive factors, specifically executive function and processing speed, may mediate adaptive functioning deficits associated with TBI.
Deficits in adaptive functioning after TBI may be most apparent in parent and teacher observations of a child’s ability to complete everyday tasks post-injury. On measures of global adaptive functioning, parents of children with severe TBI have reported greater deficits in comparison to children with mild-moderate TBI and orthopedic injuries (OI; Catroppa et al., 2008; Max et al., 1998; Taylor et al., 2002). Findings are considerably more mixed when parents are asked about specific domains of adaptive functioning. For instance, children with severe TBI exhibit deficits in the conceptual domain (e.g., communication skills) at 2 and 4 years post injury (Max et al., 1998; Stancin et al., 2002). However, the impact of TBI on the practical and social domains remains unclear, with some studies reporting deficits primarily in the social domain (Max et al., 1998) and others primarily in the practical domain (Fay et al., 1994; Greenspan & MacKenzie, 1994; Max et al., 1998; Taylor et al., 2002). When children with TBI experience adaptive functioning deficits, they are often chronic and may endure into adulthood (Catroppa et al., 2008). In comparison to healthy controls, young adults with a history of severe TBI during childhood tend to maintain fewer close friendships and experience poorer educational outcomes, higher unemployment rates, and a poorer overall quality of life 4 to 24 years post-injury (Anderson, Brown, Newitt, & Hoile, 2009; Cattelani, Lombardi, Brianti, & Mazzucchi, 1998).
The contribution of specific neuropsychological abilities to adaptive functioning in children with TBI is poorly understood. Executive function, an integrative set of higher order abilities, and processing speed, an estimate of an individual’s mental capacity and the speed of neural transmission, are two cognitive domains that are vulnerable in TBI, with deficits typically proportional to the severity of injury (Donders & Janke, 2008; Stuss, 1992). Deficits in executive function include poor attention and planning, disinhibition, poor self-regulation, difficulties in generating and implementing strategies, inability to utilize feedback, cognitive rigidity, reduced working memory, and disorganization. Given that certain adaptive functioning skills (e.g., social participation in leisure activities) are likely to rely on planning and organizational skills as well as responding to complex and evolving stimuli (e.g., functional communication, social problem solving), children with impaired executive function and slower processing speed may experience difficulty with such tasks. Caregiver behavior ratings of difficulties in executive function are related to other indications of poor overall behavioral functioning following pediatric TBI (Kurowski et al., 2013). Considering the potential limitations in relying on caregiver report of executive function (Toplak, West, & Stanovich, 2013), our study addresses the need for further exploration of the relationship between adaptive functioning in children with TBI and their performance on direct measures of executive function and processing speed.
In the current study, we expanded on previous research on childhood TBI that has focused predominantly on global adaptive functioning and overlooked the more specific AAIDD domains. Guided by the AAIDD model and taking a more comprehensive approach, we examined injury group differences at increasing levels of specificity, beginning with global functioning, then the domains of adaptive functioning defined by the AAIDD (i.e., practical, social, and conceptual), and finally differences in individual skill areas (i.e., specific subscales). This allowed us to identify the specific areas of adaptive functioning in which children with TBI experience the most daily difficulties. We then explored the contribution of executive functioning and processing speed as mediators of the specific areas of adaptive functioning identified as deficient in children with TBI.
We relied on data collected as part of a larger cross-sectional project that compared the social outcomes of 8-to-13 year old children with mild, moderate, or severe TBI to children with OI. Previous reports from this study demonstrated that children with TBI display significant deficits in social adjustment relative to children with OI (reference redacted for review) and that increases in the quality of children’s friendships were associated with better parent-reported global adaptive skills (reference redacted for review). For the current paper, we hypothesized that children with severe TBI would exhibit broad deficits in adaptive functioning when compared to children with OI, with the most pronounced deficits in conceptual and social domains. We also predicted that executive function and processing speed would both individually and collectively account for significant variance in the relation between injury severity and adaptive functioning, acting as mediators of the effects of TBI on adaptive functioning.
Method
Participants and procedure
Participants were recruited by phone from the trauma registry at three metropolitan children’s hospitals as part of the larger (name redacted for review) project (reference redacted for review). Participants were children and adolescents between the ages of 8 and 13 years who had been hospitalized for either a TBI or OI in the past 12 to 63 months. They were at least 3 years of age at the time of the injury, with the majority at least 4 years of age at the time of their injury. The TBI group included children with complicated mild to severe TBI, which was defined by the post-resuscitation Glasgow Coma Scale (GCS) score assessed by a physician within 24 hours of the injury. Severe TBI was defined by a post-resuscitation GCS score of 8 or less, and moderate TBI was defined by a GCS score from 9 to 12. Complicated mild TBI was classified based on a GCS score of 13 to 15 in association with trauma-related abnormalities on neuroimaging at the time of hospitalization; children with GCS scores of 13 to 15 without neuroimaging abnormalities were not eligible. The OI group included children who sustained fractures without loss of consciousness or other indications of brain injury (e.g., facial fracture). For the current study, children were divided into groups of severe TBI (STBI), complicated mild to moderate TBI (MTBI), and OI.
Participants were excluded on the basis of: (a) history of any prior brain injury requiring medical attention; (b) injury related to child abuse or assault; (c) premorbid neurological disorder, intellectual disability, or any sensory/motor impairment that precluded valid administration of study measures (e.g., intellectual disability); (d) history of severe psychiatric disorder requiring hospitalization; and (e) not fluent in English. Additionally, children placed in full-time special education classrooms were excluded. Premorbid learning or attention problems did not warrant exclusion, and a small subset of the sample (n = 6) had a premorbid diagnosis of Attention Deficit Hyperactivity Disorder (ADHD). The proportion of children with ADHD did not differ across injury groups. Of those who were eligible and approached about the study, 82 (47%) of those with TBI and 61 (26%) of those with OI agreed to participate. Although the participation rate was significantly higher for children with TBI, participants and non-participants did not differ in terms of age at injury, age at study contact, sex, race, or socioeconomic status (SES) based on census tract median family income. Among children with TBI, participants and non-participants did not differ on measures of injury severity.
The Institutional Review Boards at participating institutions approved all procedures, and parents completed informed consent and children provided assent before enrolling in the study. Study participation for families involved two separate visits during which parents completed ratings of children’s adaptive functioning and children completed neuropsychological testing.
The sample for the current analyses was limited to those with at least one measure of parent-reported adaptive functioning (Child and Adolescent Scale of Participation [CASP], Adaptive Behavior Assessment System-Second Edition [ABAS-II], or Behavior Assessment System for Children-Second Edition [BASC-2]; see below). Of the 143 participants in the larger project, 19 children with STBI, 50 children with MTBI, and 60 children with OI met this requirement; thus, 129 children were included in the current analyses (90.2% of the total sample). Participants included in analyses did not differ significantly from those excluded in age at injury or age at study participation, sex, SES (measured using a standardized composite based on parental education, parent occupational status, and census tract median family income), mechanism of injury, maternal education, or maternal marital status. Children with TBI were more likely to be excluded from the analyses than children with OI (15.9% vs. 1.6%; χ (143, 2) = 9.14, p =.005). The likely basis of this difference was that many children enrolled early in the study were from the TBI group and study procedures initially involved administration of measures of adaptive functioning as part of the second rather than first study visit. Children with TBI had more difficulty arranging for a friend to accompany them to the second visit, as required by the study protocol, and thus had lower rates of participation at the second time point, resulting in fewer completed adaptive functioning measures from these children. Additionally, proportionally fewer white children were excluded for analysis compared to black or multiracial children (exclusion rates of 6.3%, 33.3%, and 14.3% respectively; χ (137, 2) = 9.14, p = .01).
Demographic characteristics of the included children from the three injury groups are displayed in Table 1. The groups did not differ in sex, race, age at injury, or age at study participation. The groups differed significantly in distribution of mechanism of injury, with motor vehicle accidents being most common among children with STBI and sports/recreational injuries being most common among children with OI. Group differences in SES were not significant when injury mechanism was taken into account, consistent with epidemiological studies indicating that the risk of TBI, especially those linked to motor vehicles, is highest for children of lower SES and minority status (Brown, 2010; Howard, Joseph, & Natale, 2005; Langlois, Rutland-Brown, & Thomas, 2005). Because SES differences were confounded with injury severity, reflecting an association of lower SES with STBI, SES was not included as a covariate in data analyses (reference redacted for review).
Table 1.
Demographics, injury characteristics, and cognitive performance of the STBI, MTBI, and OI group
| STBI (n = 19) |
MTBI (n = 50) |
OI (n = 60) |
F/X2 | p | Ƞ2/V | |
|---|---|---|---|---|---|---|
| Child age at participation | 10.13 (1.60) | 10.62 (1.39) | 10.63 (1.68) | .84 | .433 | .013 |
| Child age at injury | 7.81 (2.10) | 8.02 (1.94) | 7.80 (1.82) | .20 | .817 | .003 |
| Child sex | 63% male | 68% male | 60% male | .76 | .690 | .077 |
| Child race | 88% white | 88% white | 90% white | 2.05 | .730 | .128 |
| SES | −0.48 (0.56) | −0.09 (0.98) | 0.28 (1.01) | 5.30 | .006 | .078 |
| Injury mechanism | < .001 | .532 | ||||
| MVA | 68.4% | 26.0% | 5.0% | |||
| Sports/Rec | 15.8% | 44.0% | 70.0% | |||
| Fall | 15.8% | 30.0% | 25.0% | |||
| Executive function composite | 86.4 (13.0)a | 91.9 (13.2)b | 94.78 (13.0)b | 3.15 | .046 | .048 |
| Processing speed index | 96.5 (16.0)a | 101.6 (11.1)b | 105.2 (13.9)b | 3.07 | .050 | .046 |
Note. STBI = severe traumatic brain injury, MTBI = complicated mild/moderate traumatic brain injury, OI = orthopedic injury; SES = socioeconomic status, measured using a standardized composite based on parental education, parent occupational status, and census tract median family income; MVA= motor vehicle accident. The executive function composite was created for each participant by averaging standard scores three TEA-Ch tasks (M = 100, SD= 15). The processing speed index was created by averaging the standard scores of the Cancellation and Symbol Search subtests from the Wechsler Intelligence Scales for Children-Fourth Edition for each participant (M = 100, SD =15). Values in parentheses indicate standard deviation. Superscripts indicate differences between injury groups on post hoc comparisons (p <.05).
Measures
Executive Function
Executive function was assessed using three subtests from the Test of Everyday Attention for Children (TEA-Ch; Manly, Robertson, Anderson, & Nimmo-Smith, 1999). To assess inhibitory control, children completed the Walk/Don’t Walk subtest. This subtest requires the child to mark footprints on a path for a “go” tone and inhibit marking for a “stop” tone. Auditory working memory and sustained attention was assessed using the Code Transmission subtest, in which the child listens to a series of single digit numbers and recalls the digit presented immediately before two consecutive 5s. Finally, cognitive flexibility was assessed using the Creature Counting subtest, which requires a child to count creatures, switching between counting forwards and backwards as they encounter arrows pointing up or down. These subtests have good validity and reliability, with test-retest reliability ranging from r = .73–.82 and with sensitivity to the effects of pediatric TBI (Anderson, Fenwick, Manly, & Robertson, 1998; Manly et al., 2001). Because within-group correlations for the TEA-Ch subtests were significant (rs ranging from .29–.51, all ps < .01), an executive function composite was created for each participant by averaging standard scores across the three TEA-Ch tasks. The means and standard deviation for executive function across injury groups are presented in Table 1.
Processing Speed
Processing speed was assessed using the Cancellation and Symbol Search subtests from the Wechsler Intelligence Scales for Children-Fourth Edition (WISC-IV; Wechsler, 2003). They were combined to create the Processing Speed Index (PSI), which has demonstrated sensitivity to pediatric TBI (Donders & Warschausky, 1997). The means and standard deviation for processing speed across injury groups are presented in Table 1.
Adaptive functioning
Parents completed the Adaptive Behavior Assessment System-Second Edition (ABAS-II; Harrison & Oakland, 2003) to rate their child’s ability to complete various everyday tasks. The ABAS-II consists of nine subscales, which are combined to form composites that parallel the AAIDD conceptual, social and practical domains. The Conceptual composite includes the Communication, Self-Direction, and Functional Academics subscales, assessing skills such as conversational turns, the ability to work independently, and keeping lists or reminders. The Social composite includes the Leisure and Social subscales, assessing skills such as waiting turns and listening to others. The Practical composite includes the Self-Care, Home Living, Health/Safety, and Community Use subscales, assessing skills such as rules for community safety, maintaining household duties, and finding public restrooms. The ABAS-II also yields a global composite of overall adaptive functioning, the Global Adaptive Composite (GAC). The ABAS-II has demonstrated high internal consistency (rs range from .85–.99), high test-retest reliability (rs range from .80–.90), and criterion validity in differentiating a variety of disorders.
Parents also reported on adaptive functioning using the Behavior Assessment for Children-Second Edition (BASC-2; Reynolds & Kamphaus, 2004). The five adaptive functioning subscales that form the Adaptive Skills Composite were included in analyses. Specifically, parents reported on Functional Communication (e.g., explaining rules), Leadership (e.g., the ability to get others to cooperate), Adaptability (e.g., transitioning to new activities), Social Skills (e.g., recognizing others’ efforts), and Activities of Daily Living (e.g., dressing skills). The BASC-2 has demonstrated high internal consistency (most rs ≥ .90).
Lastly, parents completed the Child and Adolescent Scale of Participation (CASP; Bedell, 2004), which measures the extent to which a child participates in activities and events at home, school and in the community (e.g., engaging in recreation with others). The CASP yields a total score that ranges from 0–100, with higher scores indicating higher social participation. The CASP has shown good test-retest reliability (r = .94), internal consistency (α ≥ .96), and construct and discriminant validity (Bedell, 2004).
Data analysis
Injury group differences in adaptive functioning
We examined the effect of injury group on adaptive functioning at increasing levels of specificity. To assess for group differences in overall adaptive functioning, we conducted one-way ANOVAs for the ABAS-II GAC and BASC-2 Adaptive Skills Composite. Profile analysis of the three ABAS-II domain composite scores was carried out using repeated-measures ANOVA to determine if the three injury groups demonstrated significantly distinct profiles across these composites. We opted for this approach so that we could examine the relative differences across the ABAS-II domains. Based on the AAIDD model, the subscales of the BASC-2 and the CASP were assigned to the three major domains in the AAIDD model (i.e., conceptual, social, and practical; see Table 2). Average within-group correlations confirmed the appropriateness of assignment of scales to domains (see Table 3). One-way ANOVAs were then conducted to examine group differences on each subscale, controlling for false discovery rate within each domain of analyses. Significant group differences were explored by post hoc comparisons using the Bonferroni correction.
Table 2.
Subscales of the ABAS-II, BASC-2, and CASP sorted into the AAIDD domains
| Conceptual domain | Social domain | Practical domain | |
|---|---|---|---|
| ABAS-II | Communication | Leisure | Community Use |
| Self-Direction | Social | Home Living | |
| Functional Academics | Health and Safety | ||
| Self-Care | |||
|
| |||
| BASC-2 | Adaptability | Social Skills | Activities of Daily Living |
| Functional Communication | |||
| Leadership | |||
|
| |||
| CASP | Social Participation | ||
Note. Adaptive Behavior Assessment System-Second Edition (ABAS-II), Behavior Assessment for Children-Second Edition (BASC-2), Child and Adolescent Scale of Participation (CASP), American Association for Intellectual and Developmental Disabilities (AAIDD)
Table 3.
Pooled within-group correlations between the ABAS-II domain scores, BASC-2 subscales, and CASP
| Conceptual domain (ABAS-II) |
Social domain (ABAS-II) |
Practical domain (ABAS-II) |
|
|---|---|---|---|
| Adaptability (BASC-2) |
.61 | .58 | .45 |
| Leadership (BASC-2) |
.73 | .63 | .49 |
| Functional Communication (BASC-2) |
.73 | .69 | .53 |
| Social Skills (BASC-2) |
.61 | .65 | .44 |
| Social Participation (CASP) |
.44 | .47 | .44 |
| Activities of Daily Living (BASC-2) |
.67 | .61 | .56 |
Note. Adaptive Behavior Assessment System-Second Edition (ABAS-II), Behavior Assessment for Children-Second Edition (BASC-2), Child and Adolescent Scale of Participation (CASP); All correlations are significant at p < .01.
Executive function and processing speed as mediators of adaptive functioning
After characterizing injury group differences in adaptive functioning, executive function and processing speed were examined to determine if they mediated the effects of TBI on adaptive functioning. One-way ANOVAs were initially conducted to examine whether the groups differed on measures of executive function and processing speed. We also examined correlations to determine if age at injury or time since injury should be included as moderators in the analyses. Within-group correlations between age at injury and adaptive functioning were not significant. Time since injury was modestly correlated with the ABAS-II Health and Safety score (r =−.219, p =.02) and ABAS-II Self-Care score (r = −.249, p =.008), but not with any other adaptive outcomes; we therefore chose not to treat time since injury as a moderator, both because of the inconsistent findings and to keep our analyses consistent across outcomes.
Multiple mediator models were then tested using ordinary least squares path analysis to determine the relative contributions to adaptive functioning accounted for by injury severity, executive function, and processing speed, and to assess whether executive function and processing speed mediated the effects of TBI on adaptive functioning (Preacher & Hayes, 2008). These analyses were conducted utilizing the PROCESS macro for SPSS (Hayes, 2013). In each model, injury group was entered as a categorical independent variable coded as two dichotomous dummy variables (STBI vs. OI; MTBI vs. OI), along with two mediators (executive function and processing speed), to assess their effects on adaptive functioning. Individual indirect effects for each mediator were tested controlling for the other.
Using this approach, unstandardized path coefficients (betas) are created for each individual path in the model and are scaled according to the measurement of variables. Unstandardized betas are preferred over standardized coefficients in this type of modeling, especially when independent variables are categorical (Deegan, 1978). The procedure yields tests of direct (a, b, c′), indirect (c), and total effects (i.e., combined direct and indirect effects) within each model. Individual indirect effects (c), which essentially are measured by multiplying or taking the product of the a and b direct effects, are examined using 95% bias-corrected confidence intervals based on 10,000 bootstrap samples; if the intervals for a specific indirect effect do not contain zero, the effect is considered significant. Joint indirect effects are tested using a t test, which the ratio of the mean joint indirect effect over the standard error. Our sample size provided sufficient power to detect significant mediation, assuming small to medium size direct (a and b) effects in our models (Fritz & MacKinnon, 2007). We also reported unadjusted R2 values as a measure of effect size for the total models (combined direct and indirect effects). Multiple mediator models were tested at increasing levels of specificity of adaptive functioning, examining the indirect effects of injury group (STBI vs. OI; MTBI vs. OI) via executive function and processing speed on (a) global adaptive functioning ABAS-II GAC and BASC-2 Adaptive Skills Composite, (b) each of the ABAS-II domain composites, and (c) the specific subscales from the ABAS-II, BASC-2, or CASP for which we found significant group differences.
Results
Injury group differences in adaptive functioning
Adaptive functioning composites
Table 4 reports mean parent ratings on composite measures and subscale measures of adaptive functioning for the three injury groups. We initially focused on the ABAS-II GAC and BASC-2 Adaptive Skills Composite as the most general measures of adaptive functioning. One-way ANOVAs indicated a significant effect of injury group for the ABAS-II GAC [F (2) = 4.87, p = .009, η2 = .08], but not the BASC-2 Adaptive Skills Composite [F (2) = 1.88, p = .16, η2 = .04]. Post hoc comparisons on the ABAS-II GAC indicated that the STBI group showed a deficit in overall adaptive functioning relative to both the MTBI and OI groups, which did not differ from one another.
Table 4.
Group means on adaptive functioning examined at the global, domain, and subscale levels
| Severe TBI | Complicated Mild-Moderate TBI | Orthopedic Injury | η 2 | |
|---|---|---|---|---|
| M (SD) | M (SD) | M (SD) | ||
| Global | ||||
| ABAS-II Global Adaptive Composite† | 87.93 (17.86)a | 102.36 (14.84)b | 99.14 (14.85)b | .08 |
| BASC-2 Adaptive Skills Composite | 46.56 (13.07) | 52.24 (11.16) | 52.00 (9.14) | .04 |
| ABAS-II Domains 1 | .08 | |||
| ABAS-II Conceptual | 94.94 (15.29) | 103.95 (13.35) | 102.91 (13.16) | |
| ABAS-II Social | 91.47 (17.17) | 105.21 (14.41) | 102.23 (13.67) | |
| ABAS-II Practical | 88.67 (17.21) | 99.51 (16.39) | 95.91 (15.58) | |
| Conceptual Domain | ||||
| ABAS-II Self-Direction | 8.24 (3.95) | 10.23 (3.03) | 9.50 (3.25) | .04 |
| ABAS-II Communication† | 9.65 (2.40)a | 11.08 (2.24)ab | 11.25 (2.27)b | .06 |
| ABAS-II Functional Academics | 9.59 (3.42) | 10.28 (2.83) | 10.55 (2.61) | .01 |
| BASC-2 Adaptability | 49.24 (12.59) | 51.87 (10.36) | 52.04 (9.01) | .01 |
| BASC-2 Leadership | 47.65 (12.40) | 54.53 (10.32) | 53.66 (9.69) | .05 |
| BASC-2 Functional Communication | 45.69 (10.27) | 51.50 (9.90) | 52.27 (8.78) | .06 |
| Social Domain | ||||
| ABAS-II Leisure* | 8.94 (3.09)a | 11.08 (2.80)b | 10.63 (2.69)a | .06 |
| ABAS-II Social* | 7.65 (3.97)a | 10.67 (2.94)b | 10.00 (3.06)b | .09 |
| CASP Social Participation* | 93.64 (8.80)a | 96.87 (6.19)ab | 98.53 (3.70)b | .08 |
| BASC-2 Social Skills | 48.71 (11.87) | 52.84 (11.18) | 51.30 (9.90) | .02 |
| Practical Domain | ||||
| ABAS-II Community Use | 8.80 (3.05) | 10.21 (3.11) | 9.73 (3.18) | .02 |
| ABAS-II Home Living | 7.06 (4.74) | 8.18 (4.03) | 7.43 (4.13) | .01 |
| ABAS-II Health and Safety | 9.35 (3.30) | 10.18 (2.97) | 10.07 (2.30) | .01 |
| ABAS-II Self-Care | 8.35 (3.45) | 10.10 (2.89) | 9.25 (2.97) | .04 |
| BASC-2 Activities of Daily Living | 45.71 (11.68) | 48.89 (10.79) | 49.38 (9.04) | .02 |
Note. Adaptive Behavior Assessment System-Second Edition (ABAS-II) composite and domain scores are presented as standard scores, with a normative mean of 100 and a standard deviation of 15 (lower scores indicate more problematic functioning). ABAS-II subscales are presented as scaled scores, with a normative mean of 10 and a standard deviation of 3 (lower scores indicate more problematic functioning). Behavior Assessment for Children-Second Edition (BASC-2)subscales are presented as T-scores, with a normative mean of 50 and a standard deviation of 10 (lower scores indicate more problematic functioning). Child and Adolescent Scale of Participation (CASP) scores are presented out of a total scores of 100 (lower scores indicate more problematic functioning). ABAS-II n = 112 (17 STBI, 39 MTBI, 56 OI), except for ABAS-II Practical domain and ABAS-II Global Adaptive composite n = 110 (15 STBI, 39 MTBI, 56 OI). BASC-2 n = 108 (17 STBI, 38 MTBI, 53 OI), except for the BASC-2 Functional Communication and BASC-2 Adaptive Skills Composite n = 106 (16 STBI, 38 MTBI, 52 OI). CASP Social Participation n = 129 (19 STBI, 50 MTBI, 60 OI).
Groups with different superscripts differ significantly on Bonferroni post hoc comparisons (p <.05)
p < .05 (without FDR correction)
p < .05 (with FDR correction)
Group main effect p < .05.
Adaptive functioning domains
A profile analysis (i.e., repeated-measures ANOVA) on the ABAS-II Conceptual, Social, and Practical domain composite scores revealed a significant main effect for domain, Wilks’ λ = .84, F (2, 106) = 10.43, p < .001, η2= .16, indicating that the mean scores for the three domains varied significantly across the three groups combined. In addition, the main effect of group was significant, (F(2) = 4.90, p = .009, η2=.08), indicating that the groups differed significantly across the three domains combined. Notably, however, the group by domain interaction was not significant, Wilks’ λ = .96, F (4, 212) = 1.2, p = .304, η2= .02, indicating that group differences did not vary significantly as a function of adaptive functioning domain. Again, post hoc comparisons for each domain score indicated that the STBI group showed poorer adaptive functioning relative to both the MTBI and OI groups, which did not differ from one another.
Adaptive functioning subscales
In the conceptual domain, after correcting for multiple comparisons using the false discovery rate, one-way ANOVAs did not indicate statistically significant group differences in adaptive functioning for the ABAS-II Communication, ABAS-II Functional Academics, ABAS-II Self-Direction, BASC-2 Functional Communication, or BASC- 2 Adaptability subscales. Prior to corrections, a significant effect of injury group was found for the ABAS-II Communication subscale [F (2) = 3.31, p = .04, η2 = .06].
In the social domain, one-way ANOVAs with control for the false discovery rate indicated a significant effect of injury group for the ABAS-II Leisure [F (2) = 3.55, p = .032, η2 = .06] and Social [F (2) = 5.45, p = .006, η2 = .09] subscales, as well as for the CASP Social Participation score [F (2) = 5.45, p = .005, η2 = .08]. However, the effect of group was not significant for the BASC-2 Social Skills subscale. Post hoc comparisons on the ABAS-II Leisure subscale indicated that the STBI group showed a deficit relative to the MTBI groups, but not the OI group. For the CASP Social Participation scale, the STBI group demonstrated a deficit in comparison to the OI group, but not the MTBI group. For the ABAS-II Social subscale, the STBI group displayed poorer functioning relative to both the MTBI and OI groups, which did not differ from one another.
In the practical domain, after controlling for multiple comparisons, one-way ANOVAs failed to reveal significant effects of injury group for the ABAS-II Self-Care, Community Use, Home Living, or Health and Safety subscales or for the BASC-2 Activities of Daily Living subscale.
Executive function and processing speed as mediators of adaptive functioning
One-way ANOVAs showed that the groups differed significantly on measures of executive function [F (2) = 3.15, p = .046, η2= .05] and processing speed [F (2) = 3.10, p = .050, η2= .05], with the lowest scores in the STBI group and highest scores in the OI group (see Table 1). Post hoc comparisons indicated that the STBI group performed significantly more poorly than the OI group in executive function and processing speed, but not significantly more poorly than the MTBI group; the MTBI and OI groups also did not differ significantly.
Multiple mediator models were then tested to examine the collective and individual contributions of injury group, executive function, and processing speed to adaptive functioning, and whether executive function and processing speed mediated group effects. Direct effects (a, b, c′) are summarized in Figures 1–5 (see also supplemental materials). The direct effects (c′) of injury group and joint indirect effects (c) of executive function and processing speed for STBI and MTBI and corresponding confidence intervals for each model are summarized in Table 5. The individual indirect effects of executive function and processing speed in the STBI group are presented in Table 6. Unadjusted R2 for the total models (indirect and direct effects) are presented in the text.
Figure 1.
Mediation model with direct effects (a, b, c′) for the ABAS-II Global Adaptive Composite (GAC); the joint indirect effect of executive function and processing speed was significant for the STBI group (see Table 5), but neither individual indirect effect was significant (see Table 6); † p < .10, * p < .05, ** p < .01; N = 110
Figure 5.
Mediation model with the direct effects (a, b, c′) for the ABAS-II Practical Domain; no significant indirect effects were found (see Table 5); † p < .10 * p < .05, ** p < .01; N = 110.
Table 5.
Direct and indirect effects of injury group (STBI vs. OI, MTBI, vs. OI) on adaptive functioning (indirect effects reflect mediation jointly via executive function and processing speed)
| Direct effects (c′) | Indirect effects (c) | |||||||
|---|---|---|---|---|---|---|---|---|
| c′ | t | p | c | t | p | Upper CI | Lower CI | |
| Global | ||||||||
| ABAS-II Global Adaptive Composite (GAC) | ||||||||
| STBI* | −8.72 | −1.88 | .063 | −11.21 | −2.52 | .013 | −20.01 | −2.40 |
| MTBI | 3.99 | 1.25 | .215 | 3.22 | 1.01 | .315 | −3.10 | 9.53 |
| BASC-2 Adaptive Skills Composite | ||||||||
| STBI* | −8.90 | −1.98 | .051 | −11.71 | −2.72 | .008 | −20.25 | −3.16 |
| MTBI | 2.80 | 0.92 | .362 | 1.94 | 0.64 | .526 | −4.11 | 8.00 |
|
| ||||||||
| Domains | ||||||||
| ABAS-II Conceptual Domain | ||||||||
| STBI* | −5.98 | −1.57 | .119 | −7.97 | −2.12 | .036 | −15.41 | −0.53 |
| MTBI | 1.88 | 0.67 | .505 | 1.04 | 0.37 | .714 | −4.57 | 6.64 |
| ABAS-II Social Domain | ||||||||
| STBI* | −8.52 | −2.10 | .038 | −10.76 | −2.68 | .008 | −18.71 | −2.81 |
| MTBI | 3.92 | 1.31 | .194 | 2.97 | 0.98 | .327 | −3.02 | 8.96 |
| ABAS-II Practical Domain | ||||||||
| STBI | −6.01 | −1.22 | .227 | −7.24 | −1.55 | .124 | −16.52 | 2.03 |
| MTBI | 4.00 | 1.17 | .243 | 3.60 | 1.07 | .286 | −3.05 | 10.25 |
|
| ||||||||
| Social Domain | ||||||||
| ABAS-II Leisure | ||||||||
| STBI* | −1.17 | −1.53 | .130 | −1.68 | −2.18 | .031 | −3.21 | −0.15 |
| MTBI | 0.66 | 1.17 | .25 | 0.45 | 0.78 | .439 | −0.70 | 1.60 |
| ABAS-II Social | ||||||||
| STBI* | −1.98 | −2.20 | .030 | −2.35 | −2.68 | .009 | −4.09 | −0.61 |
| MTBI | 0.83 | 1.25 | .214 | 0.67 | 1.01 | .316 | −0.64 | 1.98 |
| CASP Social Participation | ||||||||
| STBI* | −3.65 | −2.43 | .017 | −4.89 | −3.27 | .001 | −7.86 | −1.93 |
| MTBI | −1.19 | −1.12 | .265 | −1.66 | −1.52 | .130 | −3.82 | 0.50 |
Note. Adaptive Behavior Assessment System-Second Edition (ABAS-II), Child and Adolescent Scale of Participation (CASP); 95% confidence intervals;
p < .05 for the indirect effect.
Table 6.
Indirect effects of STBI on adaptive functioning as compared to OI (indirect effects reflect mediation via executive function and processing speed individually)
| Indirect effects (c) | |||
|---|---|---|---|
| c | Lower CI | Upper CI | |
| Global | |||
| ABAS−II Global Adaptive Composite (GAC) | |||
| Executive Function | −1.68 | −6.00 | 1.03 |
| Processing Speed | −0.81 | −4.19 | 0.87 |
| BASC−2 Adaptive Skills Composite | |||
| Executive Function | −2.51 | −7.52 | 0.26 |
| Processing Speed | −0.31 | −3.15 | 1.75 |
|
| |||
| Domains | |||
| ABAS−II Conceptual Domain | |||
| Executive Function | −1.59 | −5.45 | 0.11 |
| Processing Speed | −0.40 | −3.13 | 0.59 |
| ABAS−II Social Domain | |||
| Executive Function* | −1.96 | −6.26 | −0.05 |
| Processing Speed | −0.29 | −2.90 | 0.87 |
|
| |||
| Social Domain | |||
| ABAS−II Leisure | |||
| Executive Function* | −0.49 | −1.36 | −0.05 |
| Processing Speed | −0.02 | −0.43 | 0.26 |
| ABAS−II Social | |||
| Executive Function | −0.23 | −1.05 | 0.13 |
| Processing Speed | −0.14 | −0.78 | 0.10 |
| CASP Social Participation | |||
| Executive Function | −0.56 | −1.92 | 0.13 |
| Processing Speed* | −0.68 | −2.33 | −0.01 |
Note. Adaptive Behavior Assessment System−Second Edition (ABAS−II), Child and Adolescent Scale of Participation (CASP). No individual indirect effects of MTBI via executive function or processing speed on adaptive functioning were significant.
95% confidence interval for indirect effect does not include 0.
Adaptive functioning composites
When both executive function and processing speed were included in the model, their joint indirect effect on the ABAS-II GAC was significant for the STBI group, but not the MTBI group (R2 =0.11, see Figure 1 and Table 5). Similarly, the joint indirect effect of executive function and processing speed was significant for the BASC-2 Adaptive Skills Composite for the STBI group, but not the MTBI group (R2= .12, see Figure 2 and Table 5). However, neither executive function nor processing speed had significant indirect effects in the STBI group when considered individually (see Table 6).
Figure 2.
Mediation model with direct effects (a, b, c′) for the BASC-2 Adaptive Skills Composite; the joint indirect effect of executive function and processing speed was significant for the STBI group (see Table 5), but neither individual indirect effect was significant (see Table 6); † p < .10, * p < .05, ** p < .01; N = 104.
Adaptive functioning domains
For the ABAS-II Conceptual Domain composite, the joint indirect effect of executive function and processing speed was significant for the STBI group, but not the MTBI group (R2 = .09, see Figure 3 and Table 5). However, neither executive function nor processing speed were individually significant as mediators for the STBI group (see Table 6). For the ABAS-II Social Domain composite, the joint indirect effect of executive function and processing speed was significant for the STBI group, but not the MTBI group (R2 = .14, see Figure 4 and Table 5). The individual indirect effect of executive function was significant for the STBI group, but the individual indirect effect of processing speed was not (see Table 6). No significant indirect effects were found for the ABAS-II Practical Domain composite (R2 =.52, see Figure 5 and Table 5).
Figure 3.
Mediation model with the direct effects (a, b, c′) for ABAS-II Conceptual Domain; the joint indirect effect of executive function and processing speed was significant for the STBI group (see Table 5), but neither individual indirect effect was significant (see Table 6); † p < .10, * p < .05, ** p < .01; N = 112.
Figure 4.
Mediation model with the direct effects (a, b, c′) for the ABAS-II Social Domain; the joint indirect effect of executive function and processing speed was significant for the STBI group (see Table 5), and the individual indirect effect for executive function was significant (see Table 6); † p < .10, * p < .05, ** p < .01; N = 112.
Adaptive functioning domain subscales
Multiple mediator models were tested for the three subscales for which there were significant group differences: CASP Social Participation score, ABAS-II Leisure, and ABAS-II Social. Statistics for the joint and individual indirect effects of injury group via executive function and processing speed and corresponding confidence intervals are presented in Tables 5 and 6. For all three scales (see Supplemental Figures 1–3), the joint indirect effect of executive function and processing speed was significant for the STBI group, but not the MTBI group (see Table 5). For the ABAS-II Leisure subscale, executive function was a significant individual mediator of the effect of STBI, but processing speed was not (R2 = .13, see Table 6). For the ABAS-II Social subscale, only the joint indirect effect was significant in the STBI group; neither executive function nor processing speed was individually significant as a mediator (R2 = .12, see Table 6). In contrast, for the CASP Social Participation score, processing speed was a significant individual mediator of the effect of STBI on social participation, whereas executive function was not (R2 = .15, see Table 6).
Discussion
Pediatric TBI has the potential to impact adaptive functioning years after injury. In this study, we systematically identified injury group differences in adaptive functioning at the global, domain, and subscale level approximately 2 years following TBI. We found group differences in global adaptive functioning related to TBI severity, with children with severe TBI exhibiting more pronounced deficits than children with mild or moderate TBI (Max et al., 1998; Taylor et al., 2002). When subscales were grouped in domains in accordance with the AAIDD model, children with severe TBI displayed the most consistent impairments in the social domain. Specifically, the severe TBI group exhibited impairments relative to children with OI in social skills, social participation, and leisure activities.
In accordance with previous studies, the most pronounced deficits in adaptive functioning displayed by children with severe TBI were thus in social adjustment, with lesser deficits in the practical and conceptual domains (Fletcher et al., 1996; Max et al., 1998). Although significant group differences were not detected on the individual subscales in the practical and conceptual domains, evidence of diminished functioning in those domains was apparent in the profile analysis, as reflected in a significant group main effect and a non-significant group by domain interaction. Children with severe TBI demonstrated deficits in the practical domain years after injury, as evidenced by their low practical domain composite scores in comparison to norms (M = 88.67, SD = 17.21). One explanation for the lack of significant differences between injury groups on the practical domain scores is that the OI comparison group also scored relatively low in this domain (M = 95.91, SD = 15.58). Within the conceptual domain, our findings are consistent with research indicating that children with TBI typically recover from overt aphasic disturbances, but may demonstrate more subtle persistent deficits in the pragmatic aspects of language (Chapman, 1995). For example, children with severe TBI have difficulties understanding ambiguous sentences, making inferences, and explaining figurative expressions; they also tell briefer and less organized stories than controls (Chapman, 1995). Furthermore, communication deficits in children with severe TBI may influence other aspects of daily living, especially the quality of social relationships.
Another purpose of our study was to explore the individual and collective impact of executive function and processing speed as mediators of the effects of TBI on adaptive functioning. Our analyses indicate that executive function and processing speed jointly were significant mediators of the severe TBI group’s deficits in global adaptive functioning and in the domains of conceptual and social functioning. The magnitude of mediated effects can be estimated based on the unstandardized path coefficients yielded by the PROCESS analysis. For example, in the ABAS-II Social Domain (see Figure 4), a severe TBI is predicted to yield a 7.93 point decline in the executive function standard score, and each 1 standard score point decrease in executive function is predicted to yield a.25 point decrease in the ABAS-II Social Domain score. Thus, a severe TBI is predicted to result in a 1.98 point decrease (i.e., 7.93 × 0.25) in the ABAS-II Social Domain score that is indirectly mediated by executive function. This can be compared to the 8.52 point decline predicted by the direct effect of severe TBI. In most cases, executive function and processing speed did not entirely account for the effect of severe TBI on adaptive functioning, as reflected in significant direct effects of severe TBI, suggesting that future research is needed to identify additional cognitive mediators of the relationship between TBI and adaptive functioning.
For instance, our findings are consistent with recent models that view social adjustment as dependent in part on several higher order cognitive skills (Beauchamp & Anderson, 2010; Yeates et al., 2007). The present study focused exclusively on the contributions of executive function and processing speed to social adjustment. Previous reports from the parent study have identified theory of mind, but not executive function, as a mediator of the association between injury severity and social adjustment (references redacted for review). However, other research suggests that executive function may also contribute to theory of mind, and therefore may also impact social problem solving skills and social adjustment (Dennis et al., 2009; Muscara, Catroppa, & Anderson, 2008).
For certain outcomes, executive function and processing speed were identified as individual mediators of the effects of severe TBI on adaptive functioning. Executive function was an individual mediator of adaptive functioning for the ABAS-II social domain score, as well as the Leisure subscale. Children with severe TBI experience cognitive rigidity, poor self-regulation, and reduced memory capacity, which may be significant barriers to effective communication with others and may negatively impact the quality of their social interactions. In contrast, processing speed was a significant individual mediator of the effect of severe TBI on social participation. This finding is consistent with prior research demonstrating associations of lower social participation after TBI with greater cognitive deficits, including slower processing speed (Bedell, 2004; Gale & Prigatano, 2010). We speculate that children with severe TBI who have impaired processing speed have difficulty initiating and maintaining involvement in rapidly evolving social situations.
In contrast, for both measures of global adaptive functioning, as well as for the ABAS-II Conceptual domain and Social subscale, executive function and processing speed were joint mediators of adaptive functioning in the severe TBI group, but neither emerged as an individually significant mediator. This could occur statistically because executive function and processing speed are correlated, and their joint effects reflect shared variance. Conceptually, their joint effects as mediators may be indicative of the contribution of higher-order cognitive skills more generally to adaptive functioning.
Although the current study contributes to our understanding of adaptive functioning after pediatric TBI, several limitations should be noted. The study was exploratory in nature, and thus, replication is necessary to confirm our findings. Additionally, the study was limited by a small sample in the severe TBI group, a cross-sectional design, and a reliance on parent-reported outcomes. Past research suggests that deficits in the social domain may emerge over time, while practical deficits recover (Chapman et al., 2010; Max et al., 1998). Because deficits in adaptive functioning can have long-lasting implications for productivity and quality of life for survivors of TBI (Anderson et al., 2012; Cattelani et al., 1998), longitudinal monitoring would assist in designing interventions to prevent or remediate deficits, as well as in optimizing the timing of interventions. Another limitation is that our results may not generalize to the broader population of children with TBI given the relatively low proportion of non-white children included in the sample. Finally, the study did not examine other potential moderators of injury effects such as pre-injury functioning, time since injury, or family functioning (Anderson, Godfrey, Rosenfeld, & Catroppa, 2012; Taylor et al., 2002).
In summary, the current findings indicate that children with a history of severe TBI experience persistent post-injury deficits in adaptive functioning. Specifically, children with severe TBI experience deficits that are most pronounced in the social domain of adaptive functioning, with individual skill deficits in social participation, leisure, and social adjustment. Lesser deficits are apparent in conceptual and practical domains. The results also suggest that deficits in executive function and processing speed may partially mediate the adverse effects of severe TBI on adaptive functioning. Evidence-based rehabilitation programs are needed to address the specific deficits in adaptive functioning identified here. Interventions that target specific adaptive functioning deficits and the cognitive skills contributing to these deficits have the potential to improve the overall quality of life and functioning for survivors of pediatric TBI.
Supplementary Material
Acknowledgments
This research was supported in part by grant 5 R01 HD048946 from the National Institute of Child Health and Human Development to Keith Owen Yeates.
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