A Combined Interventional Approach to Train Interview Skills in Autistic Transition-Age Youth.

BACKGROUND: The job interview can be challenging for autistic adolescents considering the required social communication skills. Further, having decreased awareness of personal strengths may make it difficult to advocate for oneself to a future employer. The purpose of the current pilot randomized controlled trial (RCT) is to examine the preliminary efficacy and feasibility of a combined interventional approach using: the Virtual Interview Tool for Autistic Transition-Age Youth (VIT-TAY) and Kessler Foundation Strength Identification and Expression (KF-STRIDE). METHOD: Twenty autistic transition-age youth (TAY) were randomly assigned to two groups: an intervention group (n = 10) that received 9 h of VIT-TAY (interviewing practice with a virtual human), and three lessons of KF-STRIDE (positive psychology intervention to learn and discuss one's personal character strengths) and a services-as-usual (SAU) group (n = 10). The primary outcome was measured using a video-recorded mock job interview performed at pre- and post-test, which was rated by blinded assessors. Secondary outcomes included self-reports of job interview skill, interview anxiety, work readiness and recent job search behavior. RESULTS: Paired samples t-tests revealed significant differences between pre- and post-test in the intervention group (but not the control group) on the mock interview total score (p = 0.02, d = 0.76) and self-reported job interview skills total score (p = 0.02, d = 0.75). The intervention group (but not the control group) had improvements in work-readiness (p = 0.06, d = 0.53) and job search behavior (p = 0.07, d = 0.52) that were characterized by medium effect sizes. CONCLUSIONS: This pilot study suggests that combining VIT-TAY with KF-STRIDE leads to improvements in performance-based and self-reported job interview skills.

Neurobehavioral Symptoms in Spanish-Speaking Individuals With Subconcussive Injuries.

OBJECTIVE: To examine whether exposure to high-risk events causing injury to the head or neck has an effect on neurobehavioral symptoms in the absence of an alteration of consciousness in Spanish-speakers. SETTING: Web-based survey. PARTICIPANTS: Seven hundred forty-eight individuals from Spain and Latin America, aged 18 to 65 years, with 10 years or more of education. Thirty-nine participants failed quality checks and were excluded. Seven hundred nine participants were included in the analyses. DESIGN: Cross-sectional study. Subconcussive exposure was defined as endorsing exposure to one or more high-risk scenarios in the absence of any alteration of consciousness. Three injury groups were derived: No Head Injury, Subconcussive Exposure, and traumatic brain injury (TBI). The Subconcussive Exposure group was further divided into Single and Multiple Exposures. Two analyses were conducted: the effect of lifetime exposure to injury (No Head Injury, Subconcussive Exposure, TBI) on neurobehavioral symptoms; the effect of Subconcussive Exposure Frequency (No Head Injury, Single Exposure, Multiple Exposures) on neurobehavioral symptoms. MAIN MEASURES: Spanish Ohio State University Traumatic Brain Injury Identification Method Self-Administered-Brief (OSU TBI-ID SAB); Neurobehavioral Symptom Inventory (NSI). RESULTS: There was a significant effect for Injury group on the NSI partial eta-squared (ηp2 = 0.053) and a significant effect of Exposure Frequency group on the NSI (ηp2 = 0.40). Individuals with subconcussive exposures reported significantly more neurobehavioral symptoms than those with no history of head injury and significantly less symptoms than those with TBI. Individuals with multiple subconcussive exposures reported significantly more neurobehavioral symptoms than those with single and no exposure. CONCLUSION: This research expands the utility of the OSU-TBI-ID SAB as a lifetime TBI history assessment tool to one capable of evaluating subconcussive exposure dosing effects in Spanish-speakers. Such an index may facilitate establishment of subconcussive exposure prevalence rates worldwide, leading to improved understanding of the chronic effects of high-risk exposures.

Exercise as a behavioral approach to improve mood in persons with traumatic brain injury.

Mood disturbance is a common, long-term, negative consequence of traumatic brain injury (TBI) that is insufficiently addressed by most traditional treatment modalities. A large body of evidence supports the efficacy of exercise training (ET) to broadly improve mood, as measured most often by the Profile of Mood States (POMS). However, this behavioral approach is not used nearly enough in the TBI population, and when it is, mood is rarely measured. This scoping review will evaluate the use of POMS as a mood measure in TBI research and to establish a rationale for using ET as a behavioral approach to broadly improve mood in persons with TBI.

Visuomotor misalignment induced through immersive virtual reality to improve spatial neglect: a case-series study.

One evidence-based treatment for spatial neglect is prism adaptation (PA) treatment. PA after-effects, i.e., the implicit shifts in the arm reaching position toward the neglected side of space after prism removal, are considered fundamental to PA treatment effects. In the present study, the arm reaching position was shifted through a visuomotor misalignment procedure using immersive virtual reality (VR). To examine whether this procedure might have a beneficial impact on spatial neglect, we conducted a multi-baseline experiment in three individuals with chronic left-sided neglect post stroke. Improved spatial neglect was observed in all participants immediately after 5 sessions with two rounds in each. Two participants demonstrated lasting or continuous improvement two weeks later. Participants' pattern of brain lesions did not appear to clearly explain performance differences. The findings suggest that VR-induced visuomotor misalignment may improve spatial neglect immediately after a multi-session treatment course. The optimal number of sessions will be determined by future studies with a larger sample size, which may also elucidate the number of sessions sufficient for sustained improvement in most patients. Further investigations will identify the neural mechanisms underlying VR-induced visuomotor misalignment, which may or may not be identical to PA after-effects.

Rationale and methodology for examining the acute effects of aerobic exercise combined with varying degrees of virtual reality immersion on cognition in persons with TBI.

Persons with Traumatic Brain Injury (TBI) commonly present with long-term cognitive deficits in executive function, processing speed, attention, and learning and memory. While specific cognitive rehabilitation techniques have shown significant success for deficits in individual domains, aerobic exercise training represents a promising approach for an efficient and general treatment modality that might improve many cognitive domains concurrently. Existing studies in TBI report equivocal results, however, and are hampered by methodological concerns, including small sample sizes, uncontrolled single-group designs, and the use of suboptimal exercise modalities for eliciting cognitive improvements in this population. One particularly promising modality involves the application of environmental enrichment via virtual reality (VR) during aerobic exercise in persons with TBI, but this has yet to be investigated. One approach for systematically developing an optimal aerobic exercise intervention for persons with TBI involves the examination of single bouts of aerobic exercise (i.e., acute aerobic exercise) on cognition. Acute exercise research is a necessary first step for informing the development of high-quality exercise training interventions that are more likely to induce meaningful beneficial effects. To date, such an acute exercise paradigm has yet to be conducted in persons with TBI. To that end, we propose an acute exercise study that will investigate the acute effects of aerobic exercise with incremental degrees of environmental enrichment (VR) relative to a control comparison condition on executive function (divided attention and working memory) and processing speed in 24 people with TBI.

Validation of the Norma Latina neuropsychological assessment battery in individuals with multiple sclerosis in Mexico.

BACKGROUND: Between 50-60% of Multiple Sclerosis (MS) patients have cognitive alterations. There are several batteries to assess cognitive impairments in MS, however, few exist for Latin Americans. The objective of this study is to evaluate the neuropsychological profile of Mexican people with MS (PwMS) and assess the utility of Norma Latina, a new battery for cognitive assessment in Latin America, in differentiating cognitive test performance between PwMS and healthy controls (HCs). METHODS: 100 PwMS and 100 HCs from Mexico were evaluated with the Norma Latina battery. The following analyses were conducted: 1) low-percentiles of each participant were calculated, 2) Area Under the Curve was used to determine whether the battery discriminated between PwMS and HCs, 3) four composite scores were calculated, and student's t-test was used to compare groups according to these domains. RESULTS: PwMS obtained a greater number of impaired scores compared to HCs, principally in executive function. The battery successfully discriminated between PwMS and HCs, with the strongest capacity to discriminate in the executive functions, and the weakest in memory. CONCLUSION: Establishing validation of a neuropsychological battery for Mexican PwMS will help to more accurately detect cognitive alterations, which will guide the decisions of professionals in terms of cognitive rehabilitation.

Factor analysis of the Neurobehavioral Symptom Inventory among a sample of Spanish-speakers.

ABSTRACTA study was conducted to examine the factor structure of the Neurobehavioral Symptom Inventory (NSI) among a large community sample of 729 Spanish-speakers from the Continental United States (n = 174, 23.9%), Latin America (n = 465, 63.8%), and Spain (n = 90, 12.3%) The sample was 62.1% female, had at least 10 years of formal education, and ranged in age from 18 to 65 years (M = 36.7, SD = 12.5). The sample was randomly split into two groups with comparable demographics for a sequential analysis that consisted of an exploratory factor analysis on the first subsample followed by a confirmatory factor analysis within a second validation subsample. Results demonstrated a high internal consistency reliability for the Spanish version of the NSI, and a three-factor solution was supported with somatic, affective, and cognitive factors. Findings were comparable to prior studies with the English version of the NSI providing preliminary support for the construct validity of this measure among a large sample of Spanish-speakers. Further study is needed to determine the criterion-related validity of the individual factors as separate subscales and to examine the appropriateness of this measure for individuals with lower levels of education.

The preliminary effects of moderate aerobic training on cognitive function in people with TBI and significant memory impairment: a proof-of-concept randomized controlled trial.

This single-blinded RCT investigated cognitive effects of aerobic exercise in persons with TBI-related memory impairment. Five participants . were randomly assigned to 12-weeks of either supervised moderate intensity aerobic cycling or an active control. Outcome measures included neuropsychological assessments and structural neuroimaging (MRI,). The exercise group demonstrated greater improvements on auditory verbal learning (RAVLT; d=1.54) and processing speed (SDMT; d=1.58). The exercise group showed larger increases in volume of the left hippocampus (d=1.49) and right thalamus (d=1.44). These pilot data suggest that 12-weeks of moderate intensity aerobic cycling may improve memory and processing speed in those with TBI-related memory impairments.

Mood and emotional disorders associated with parkinsonism, Huntington disease, and other movement disorders.

This chapter provides a review of mood, emotional disorders, and emotion processing deficits associated with diseases that cause movement disorders, including Parkinson's disease, Lewy body dementia, multiple system atrophy, progressive supranuclear palsy, corticobasal degeneration, frontotemporal dementia with parkinsonism, Huntington's disease, essential tremor, dystonia, and tardive dyskinesia. For each disorder, a clinical description of the common signs and symptoms, disease progression, and epidemiology is provided. Then the mood and emotional disorders associated with each of these diseases are described and discussed in terms of clinical presentation, incidence, prevalence, and alterations in quality of life. Alterations of emotion communication, such as affective speech prosody and facial emotional expression, associated with these disorders are also discussed. In addition, if applicable, deficits in gestural and lexical/verbal emotion are reviewed. Throughout the chapter, the relationships among mood and emotional disorders, alterations of emotional experiences, social communication, and quality of life, as well as treatment, are emphasized.

Assessing lifetime exposure to traumatic brain injury among an international sample of Spanish speakers.

BACKGROUND: With structured interviews being an established method for assessing one's exposure to traumatic brain injury across their lifetime, effective assessment tools are needed to serve the large population of Spanish speakers in the U.S. and abroad. OBJECTIVE: To obtain preliminary evidence of validity for a Spanish version of a web-based, structured interview designed to assess lifetime exposure to TBI. METHODS: A sample of 720 Spanish-speaking individuals between the ages of 18 through 65 from the continental U.S. (34.3%), South America (30.8%), the Caribbean (12.6%), Spain (12.4%), and Mexico and Central America (9.9%) completed an online survey containing the Ohio State University Traumatic Brain Injury Identification Method (Self-Administered-Brief; OSU TBI-ID SAB), Neurobehavioral Symptom Inventory, and PROMIS Cognitive Concerns Scale. RESULTS: Indices of severity of worst TBI, time since most recent TBI, and multiple injuries demonstrated expected relationships with neurobehavioral symptoms such that greater symptom reporting was observed among those who had more severe injuries, more recent injuries, and multiple injuries over a period of time. CONCLUSIONS: Findings provide preliminary evidence of validity for three of the indices derived from OSU TBI-ID SAB among Spanish-speaking individuals. Further study is needed to assess other aspects of this instrument to pave the way for further epidemiological studies involving lifetime exposure to TBI among Spanish-speaking individuals across the U.S., Spain, and Latin America.

Efficacy of the Spanish modified Story Memory Technique in Mexicans with multiple sclerosis: A pilot randomized controlled trial.

BACKGROUND: Memory impairments commonly afflict individuals with MS. While evidence-based cognitive rehabilitation treatments are available in English, the lack of such interventions in Spanish is an important barrier to care for Hispanics with MS. There is class I evidence that the modified Story Memory Technique (mSMT) improves learning in English. This intervention has been translated and adapted into Spanish. OBJECTIVE: To examine the preliminary efficacy of the Spanish mSMT to improve learning in Mexicans with MS. METHODS: Twenty individuals with relapsing-remitting MS were randomized to treatment (n = 10) or placebo control (n = 10) groups. The Spanish mSMT is a 10-session intervention that teaches imagery and context to facilitate learning. The control condition was matched to the treatment condition in treatment duration, and stimulus content and presentation. Participants completed baseline and post-treatment neuropsychological assessments. RESULTS: Individuals who received the Spanish mSMT showed significant improvements in learning and life satisfaction relative to the control group. Also observed were a near-moderate effect size on perceived memory complaints and a moderate-to-large effect size on the family's perception of the patient's competency. CONCLUSIONS: The Spanish mSMT showed preliminary efficacy in improving learning deficits in Mexicans with MS, and such improvements may extend to other domains.

Cognitive Reserve Protects Against Memory Decrements Associated With Neuropathology in Traumatic Brain Injury.

OBJECTIVE: To evaluate whether cognitive reserve (CR) moderates the relationship between neuropathology and cognitive outcomes after traumatic brain injury (TBI). SETTING: Outpatient research organization. PARTICIPANTS: Patients with complicated mild (n = 8), moderate (n = 9), and severe (n = 44) TBI. DESIGN: Prospective, cross-sectional study. MAIN MEASURES: Cognitive reserve was estimated using a test of word reading (Wechsler Test of Adult Reading). Diffusion tensor imaging (functional anisotropy) was used to quantify neuropathology. Neuropsychological test scores were submitted to principal components analyses to create cognitive composites for memory, attention, executive function, and processing speed domains. RESULTS: At lower levels of neuropathology, people with higher CR exhibited better memory than those with lower CR. This benefit diminished as neuropathology increased and disappeared at the highest levels of neuropathology. Cognitive reserve ceased exerting a protective effect at premorbid intelligence levels below average. CONCLUSION: Cognitive reserve may differentially protect some cognitive domains against neuropathology relative to others. A clinical cutoff below which CR is no longer protective, together with a possible neuropathology ceiling effect, may be instructive for prognostication and clinical decision-making in cognitive rehabilitation.

The factor structure of the Disability Rating Scale in individuals with traumatic brain injury.

PURPOSE: To examine the factor structure of the Disability Rating Scale and the predictive validity of the scale's factors among individuals with traumatic brain injury. MATERIALS AND METHODS: Five hundred and eight individuals with moderate-to-severe traumatic brain injury were administered the Disability Rating Scale. The sample was randomly divided into two groups. An exploratory factor analysis was conducted on Group 1, and a confirmatory factor analysis on Group 2. Regressions were performed to determine the predictive ability of the factors. RESULTS: The exploratory factor analysis generated a three-factor structure, explaining 82.1% of the variance. Factor 1, comprising three disability items (feeding, toileting, and grooming), accounted for 58.4% of the variance. Factor 2, comprising three impairment items (eye opening, communication ability, and motor response), accounted for 14.8% of the variance. Factor 3, comprising two handicap items (level of functioning and employability), accounted for 8.9% of the variance. The three-factor solution was confirmed by confirmatory factor analysis. Regressions revealed the impairment factor at admission and the disability factor at discharge accounted for unique variance in predicting functional outcomes at one year post-injury. CONCLUSION: Each factor of the Disability Rating Scale may independently serve as a clinically useful outcome predictor after traumatic brain injury. Implications for rehabilitation The Disability Rating Scale is a measure used in brain injury rehabilitation that generates a total score indicating level of disability. This study confirmed a three-factor structure and showed that the individual factor scores provide unique information in predicting rehabilitation outcomes at one year post-injury.

Relationship Between Hispanic Nativity, Residential Environment, and Productive Activity Among Individuals With Traumatic Brain Injury: A TBI Model Systems Study.

OBJECTIVE: To examine the influence of nativity and residential characteristics on productive activity among Hispanics at 1 year after traumatic brain injury (TBI). SETTING: Acute rehabilitation facilities and community follow-up. PARTICIPANTS: A total of 706 Hispanic individuals in the TBI Model Systems National Database. DESIGN: Secondary data analysis from a multicenter longitudinal cohort study. MAIN MEASURES: Nativity (foreign born or US native), productive activity derived from interview questions regarding employment status, and other demographic information. Census data were extracted by zip code to represent residential characteristics of aggregate household income and proportion of foreign language speakers (FLS). RESULTS: Among foreign-born individuals with TBI, those living in an area with a higher proportion of FLS were 2.8 times more likely to be productive than those living in areas with a lower proportion of FLS. Among individuals living in an area with a lower proportion of FLS, US-born Hispanics were 2.7 times more likely to be productive compared with Hispanic immigrants. CONCLUSION: The relationship between nativity and productive activity at 1 year post-TBI was moderated by the residential proportion of FLS. Findings underscore the importance of considering environmental factors when designing vocational rehabilitation interventions for Hispanics after TBI.

Reciprocal Causation Between Functional Independence and Mental Health 1 and 2 Years After Traumatic Brain Injury: A Cross-Lagged Panel Structural Equation Model.

OBJECTIVE: The research attempting to disentangle the directionality of relationships between mental health and functional outcomes after traumatic brain injury (TBI) is growing but has yielded equivocal findings or focused on isolated predictors or isolated outcomes. The purpose of the current study was to use cross-lagged panel and structural equation modeling (SEM) techniques to examine causality between comprehensive indices of mental health (depression, anxiety, and life satisfaction) and functional independence in a national sample of individuals with TBI over the first 2 years after injury. DESIGN: Participants were 4,674 individuals with TBI from the TBI Model Systems Database. RESULTS: The SEM, which yielded good fit indices, suggested that individuals with TBI with greater mental health problems at 1 and 2 years after injury had lower functional independence at those same time points. The standardized path loadings for mental health problems and for functional independence over time were large, suggesting a high degree of consistency in mental health and functional independence across 1 and 2 years. In terms of cross-lag, mental health at Time 1 did not exert a unique effect on functional independence at Time 2, but functional independence at Time 1 exerted a statistically significant but quite small unique effect on mental health at Time 2. CONCLUSIONS: This combination of results suggests that functional independence is only slightly more causal than mental health in the relationship between mental health and functional independence over the first 2 years post-TBI, and that instead, reciprocal causality is a more likely scenario. TO CLAIM CME CREDITS: Complete the self-assessment activity and evaluation online at http://www.physiatry.org/JournalCME CME OBJECTIVES: Upon completion of this article, the reader should be able to: (1) understand the nature of the relationship between mental health problems and functional independence after traumatic brain injury; (2) learn about a novel methodological technique for examining the connections between variables over time; and (3) understand when ongoing support for individuals with traumatic brain injury is necessary. LEVEL: Advanced ACCREDITATION: The Association of Academic Physiatrists is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.The Association of Academic Physiatrists designates this activity for a maximum of 1.5 AMA PRA Category 1 Credit(s)™. Physicians should only claim credit commensurate with the extent of their participation in the activity.

Comparison of FIM™ communication ratings for English versus non-English speakers in the traumatic brain injury model systems (TBIMS) national database.

OBJECTIVE: To examine the effect of primary language on admission and discharge FIM™ communication ratings in a sample of individuals with moderate-to-severe traumatic brain injury (TBI). DESIGN AND METHODS: Secondary data analysis of rehabilitation admission and discharge FIM™ communication ratings of 2795 individuals hospitalized at a Traumatic Brain Injury Model Systems (TBIMS) centre between 2007-2012. RESULTS: Individuals who spoke no English were rated worse on functional communication outcomes at inpatient rehabilitation discharge relative to individuals whose primary language was English. CONCLUSIONS: These findings may reflect systematic bias in FIM™ communication ratings of non-English-speaking individuals with TBI and/or TBI-induced communication difficulties in non-English-speaking individuals. Clinical and research implications are discussed.

The Multidimensional Influence of Acculturation on Digit Symbol-Coding and Wisconsin Card Sorting Test in Hispanics.

OBJECTIVE: The purpose of the current study was to evaluate the relative contribution of acculturation to two tests of nonverbal test performance in Hispanics. METHOD: This study compared 40 Hispanic and 20 non-Hispanic whites on Digit Symbol-Coding (DSC) and the Wisconsin Card Sorting Test (WCST) and evaluated the relative contribution of the various acculturation components to cognitive test performance in the Hispanic group. RESULTS: Hispanics performed significantly worse on DSC and WCST relative to non-Hispanic whites. Multiple regressions conducted within the Hispanic group revealed that language use uniquely accounted for 11.0% of the variance on the DSC, 18.8% of the variance on WCST categories completed, and 13.0% of the variance in perseverative errors on the WCST. Additionally, years of education in the United States uniquely accounted for 14.9% of the variance in DSC. CONCLUSIONS: The significant impact of acculturation on DSC and WCST lends support that nonverbal cognitive tests are not necessarily culture free. The differential contribution of acculturation proxies highlights the importance of considering these separate components when interpreting performance on neuropsychological tests in clinical and research settings. Factors, such as the country where education was received, may in fact be more meaningful information than the years of education of education attained. Thus, acculturation should be considered an important factor in any cognitive evaluation of culturally diverse individuals.

Does slowed processing speed account for executive deficits in multiple sclerosis? Evidence from neuropsychological performance and structural neuroimaging.

OBJECTIVE: Executive deficits and slow processing speed (PS) are observed in persons with multiple sclerosis (MS). The question of whether executive deficits can be explained by slow PS was examined with neuropsychological measures and a neurostructural measure (brain atrophy). METHOD: Fifty MS patients were compared with 28 healthy controls (HCs) on tasks of executive functioning with and without a PS element (e.g., Trail Making Test and Wisconsin Card Sorting Test). RESULTS: The MS group performed worse than HCs on speeded tasks of executive function. However, after controlling for speed, group differences on executive tasks disappeared. There were also no group differences on executive tasks with no PS demands. The effect of disease progression on executive task performance was assessed in the MS group. Higher atrophy in MS participants was associated with greater deficits on speeded executive tasks, but this association disappeared when controlling for PS. There was no association between atrophy and performance on nonspeeded executive tasks. CONCLUSIONS: Our results support the notion that executive deficits in MS may be explained by slow PS. These findings highlight the role of slowed PS as a primary impairment underlying other cognitive functions. Disentangling the relative contribution of PS to executive function is an important step toward the development of appropriate rehabilitation strategies for persons with MS.

Racial/ethnic disparities in mental health over the first 2 years after traumatic brain injury: a model systems study.

OBJECTIVE: To determine whether racial/ethnic disparities occur in depression, anxiety, and satisfaction with life at 1 and 2 years postdischarge. DESIGN: A prospective, longitudinal, multicenter study of individuals with traumatic brain injury (TBI) participating in the National Institute on Disability and Rehabilitation Research Traumatic Brain Injury Model Systems project. Medical, demographic, and outcome data were obtained from the Model Systems database at baseline, as well as 1 and 2 years postdischarge. SETTING: A total of 16 TBI Model Systems hospitals in the United States. PARTICIPANTS: Individuals with moderate or severe TBI (N=1662) aged 16 years or older consecutively discharged between January 2008 and June 2011 from acute care and comprehensive inpatient rehabilitation at a Model Systems hospital. INTERVENTION: Not applicable. MAIN OUTCOME MEASURES: The Patient Health Questionnaire-9, Generalized Anxiety Disorder 7-item scale, and Satisfaction with Life Scale assessed depression, anxiety, and satisfaction with life at 1 and 2-year follow-ups. RESULTS: After controlling for all possible covariates, hierarchal linear models found that black individuals had elevated depression across the 2 time points relative to white individuals. Asian/Pacific Islanders' depression increased over time in comparison to the decreasing depression in those of Hispanic origin, which was a greater decrease than in white individuals. Black individuals had lower life satisfaction than did white and Hispanic individuals, but only marginally greater anxiety over time than did white individuals and similar levels of anxiety as did Asian/Pacific Islanders and Hispanic individuals. CONCLUSIONS: Mental health trajectories of individuals with TBI differed as a function of race/ethnicity across the first 2 years postdischarge, providing the first longitudinal evidence of racial/ethnic disparities in mental health after TBI during this time period. Further research will be required to understand the complex factors underlying these differences.