TABLE 1.
Controlled and Single-Subject Studies of Early Intervention in Autism: 1998–2005
| Authors and Date | Sample | Outcome Measures | Treatment Procedures | Findings | Nathan and Gorman (2002) Criteria |
|---|---|---|---|---|---|
| Aldred et al. (2004) | 14 children dx with AD (M age 48 months, 13 male) in tx group and 14 children (Mdn age 51 months, 12 male) in control group. All parents Caucasian, except for 2 mothers African Caribbean. | ADOS, PSI, Vineland, semistructured parent–child interaction. | Tx group: Monthly parent-training pragmatic language workshops for 6 months, with additional 6 month follow-up of 2-monthly consolidation sessions. Parents asked to spend 30 min daily implementing techniques with child. Both groups received speech and language therapy, TEACCH, and social skills training. | Tx group showed improvements in autism severity scores, expressive vocabulary and communication (esp. for younger, lower functioning group), increased parental responsivity. No significant differences in adaptive behavior or parental stress. | Type 1 study + RCT + Blind assessments + Incl/excl criteria. + Standardized dx battery + Comparison group – Tx fidelity – Tx manual. |
| Bibby et al. (2002) | 66 children with autism or ASD (55 male, M CA 45 months at the start of receiving ongoing intervention). No other information provided. | BSID-II, BAS, Griffiths, WISC-III or WPPSI–R, Reynell, Merrill-Palmer, Vineland, school placement, behavioral ratings, parent interviews of tx information (age at onset, duration, intensity, tx personnel, supplementary tx). | Treated by 25 different early intervention consultants. Workshop-model programs provided for approximately two 6-hr days in child's home and 1-day follow-up workshops with a median frequency of 4 times/year. Teaching methods included discrete trials training and incidental teaching. Parent-selected alternative treatments (e.g., diets, vitamins, sensory treatments) for 81% of children. | No changes in group mean IQ across 31.6 months of intervention (N = 22). Vineland scores sig increased by 8.9 points to a mean of 63.4 (N = 21). No children younger than 72 months achieved normal functioning (i.e., IQ > 85 and unassisted mainstream school placement; N = 42). Gain in mental age (5.4 months), adaptive behavior (9.7 months), and language (5.1 months) were found across 12 months (N = 60). | Type 3 study – RCT – Blind assessments – Incl/excl criteria – Standardized dx battery – Comparison group – Tx fidelity + Tx manual. Other: Post-tx data only, no baseline, data. |
| Cohen et al. (2006) | 42 children ages 18–12 months dx with ASD: 21 children in EIBT treatment, matched to 21 children receiving community care. No other information provided. | ADI, ADOS, BSID-II, VABS, Reynell, Merrill-Palmer, WPPSI. | EIBT group received 35–40 hr for 3 years from trained therapists following Lovaas's manual with in home 1:1 instruction, peer play training, and regular education placements. Parents had weekly training. Comparison group received services through schools in special classes, 10–25 hr per week, ratios 1:1 to 1:3. | Sig group diff on IQ score and three of the four Vineland scores. EIBT M IQ posttreatment score 87 (25-pt. gain), comparison 73 (14-pt. gain), after 3 years. Diff on receptive language approached significance. EIBT changed from 52 to 72; comparison from 53 to 62, diff on expressive language was not sig (25 vs. 15 point gains). 17 of 21 EIBT children in regular classes in year 3, vs. 1 of 21 comparison children. | Type 2 study – RCT – Blind assessments + Incl/excl criteria. + Standardized dx battery + Comparison group + Tx fidelity + Tx manual. |
| Drew et al. (2002) | 24 children dx with autism (M CA 23 months) randomized to parent training group (N = 12; 11 male, 11 nonverbal, 1 single words) or to local services only (N = 12; 8 male, 11 nonverbal, 1 single words). No other information provided. | ADI-R, Griffiths, MCDI, PSI, parent-completed activity checklists of type and amount of health and education services every 3 months. | Parent training adopted a psycholinguistic and social-pragmatic approach to language development with emphasis on teaching joint attention skills, joint action routines, and behavioral management integrated into everyday, natural routines. Parents received in-home speech and language consultation every 6 weeks for a 3-hr session. Local services group received a mixture of services including speech and language therapy, occupational therapy, physiotherapy, some parents provided direct treatment, and 3 children received in-home 1:1 discrete trial formats (M = 33 hr/week). | No group diff on NVIQ, symptom severity, parental report of stress, or words or gestures produced at follow-up, though parent-report measures indicated greater word production and comprehension for parent training group. | Type 2 study + RCT – Blind assessments + Incl/excl criteria + Standardized dx battery + Comparison group – Tx fidelity – Tx manual. Other: Concerns about low power given small group size, uniform assessment. |
| Eikeseth et al. (2002) | 13 children dx with autism in Lovaas tx, 12 in eclectic, M CA 66 months, M IQ 62–65. Assigned based on availability of therapists. 75% male. No other information provided. | BSID-II or WISC-R or WPPSI-R, Merrill- Palmer, Reynell, Vineland, amount of tx, type of tx goals. | Both groups of children received a mean of 28 hr per week of 1:1 tx at an integrated school setting for 1 year. For the behavioral tx only, parents were required to be trained for 3 months. The eclectic tx was designed by experienced special ed staff, incorporated elements from TEACCH, sensory-motor therapies, and ABA, and delivered in 1:1 clinician-directed format. | Group diff not sig at follow-up, except in maladaptive behaviors. However, Lovaas group made sig pre–post changes, unlike eclectic group. Greater number of children in Lovaas group and IQ in normal range at posttest. | Type 2 study – RCT + Blind assessments + Incl/excl criteria + Standardized dx battery + Comparison group. + Tx fidelity + Tx manual. Other: Analytic plan clear. |
| Howard et al. (2005) | 29 children dx with AD or PDDNOS in IBT (86% male, 83% autism, 72% Caucasian, 79% married), 16 in AP (81% male, 75% autism, 50% Caucasian, 80% married), 16 in GP (100% male, 56% autism, 57% Caucasian, 56% married). | BSID-II, DP-II, Merrill-Palmer, Reynell, S-B, Vineland, WPPSI-R. Other measures used only one time for one child, while some measures used only at in-take or follow-up (missing data on intake and follow-up measures). | IBT consisted of 25–30 (younger than 3 years) or 35–40 (older than 3 years) hr/week of 1:1 intervention, includ. discrete trial, incidental teaching, parent training in behavior analytic procedures. AP consisted of public school autism classrooms (staff:child ratio of 1:1 or 1:2) of 25–30 hr/week of eclectic tx (discrete trial, PECS, SIT, TEACCH, speech therapy). GP consisted of local community special ed classrooms (staff:child ratio 1:6) of 15 hr/week with speech therapy, developmental curriculum. | No sig diff between AP and GP groups at follow-up vs. higher sig mean scores in all developmental domains (except motor) and 30 point IQ gain for IBT group. GP showed losses in multiple developmental domains. | Type 3 study – RCT – Blind assessments + Incl/excl criteria – Standardized dx battery + Comparison group – Tx fidelity + Tx manual Other: Combined approaches – not further described. |
| Ingersoll et al. (2001) | 6 children with ASD and 3 typically developing children (CA 26–41 months). No other information provided. | Videotaped samples of peer social avoidance behavior (opportunities and attempts) and language use. | Inclusive toddler tx program and day care with teacher: student ratio of 1:3. Developmentally appropriate toddler classroom activities, including Incidental Teaching and PRT. | Peer social avoidance appeared to predict outcome for subsequent peer avoidance and language use. | Type 2 study – RCT – Blind assessments + Incl/excl criteria – Standardized dx battery + Comparison group + Tx fidelity + Tx manual |
| Jocelyn et al. (1998) | 35 children dx with AD or PDDNOS randomized to exp. or control group. 34 male, ages 24–72 months (M CA 44 months), 33 Caucasian, 33% in severe range on CARS, range of SES on Hollingshead. 16 in experimental group. Mean NVIQ 58 exp. group & 67 comp group. | Autism Behavior Checklist, EIDP, Family Assessment Measure, PSDP, Stress-Arousal Checklist, and TAQ. | 12 weeks of tx delivered in a typical day care center by child care workers (and at home by parents) after 15 hr of training and additional consultation. Strategies targeted language, social, and play development, and decreasing of unwanted behaviors. Control group attended community day care alone. | Sig tx effects on language development, mother and child care worker knowledge about autism, maternal perception of control, and parent satisfaction. | Type 1 study + RCT + Blind assessments + Incl/excl criteria + Standardized dx battery + Comparison group – Tx fidelity – Tx manual Other: Sample large enough for power. Clear analytic plan |
| L. K. Koegel et al. (1999) | 10 children with autism participated in phase 1 (N = 6; M CA 42 months, M language age 27 months) and phase 2 (N = 4; M CA 37 months, M language age 23 months). No other information provided. | Pre-tx language age from archival videotapes of unstructured parent/child interactions, spontaneous initiations from 15-min videotape samples of parent–child interaction, and Vineland. Posttx data on pragmatic ratings from 15-min video samples of parent–child interactions, social and community functioning, and Vineland. | Both phases received 1.5–2 hr of PRT intervention in clinical settings and community programs for approximately 4 years, with follow through by parents that participated in parent education programs. PRT consists of motivational factors (child choice, reinforcing attempts, interspersing maintenance tasks, natural and direct reinforcers, turn taking and response to multiple cues). The motivational and self-management procedures were used to teach communication, self-help, academic, social, and recreational skills. Phase 2 intervention taught a series of verbal child-initiated questions and other initiations to elicit attention, request assistance, and seek play partners. | Phase 1 indicated that children who responded favorably to intervention exhibited more spontaneous self-initiations at pre-tx. Phase 2 showed that children who were initially poor responders to intervention could be taught a variety of self-initiations, including question-asking and achieve similarly favorable outcomes. | Type 3 study – RCT – Blind assessment + Incl/excl criteria – Standardized dx battery + Comparison group – Tx fidelity + Tx manual Other: Exploratory single-subject design with 3 ss in each of two groups. No multiple baseline designs. Outcomes are described anecdotally. |
| Luiselli et al. (2000) | 16 children started tx younger than 3 years (N = 8; M CA 2.63 years) or older than 3 years (N = 8; M CA 3.98 years). All dx with AD or PDDNOS. No other information provided. | Developmental rating checklists from ELAP or LAP. Measured hours/week of tx, duration of tx, and total hours of tx. | In-home discrete trial and incidental teaching 6–20 hr/week over 5–22 months. | Children received tx before 3 years showed sig developmental changes but no between group diff. Overall improvement in communication, cognitive, and social-emotional functioning predicted by duration of time in tx. | Type 3 study – RCT – Blind assessment – Incl/excl criteria – Standardized dx battery – Comparison group – Tx fidelity + Tx manual Other: Retrospective study. Measures not standardized. |
| Mahoney & Perales (2003) | 20 children with AD or PDDNOS, M CA 32 months, 60% male. M CA of mothers 34 years, 95% were Caucasian, 100% were married, M average of 15.5 years of education, and 60% were in middle-upper SES. | Videotaped samples of mother-child interactive behaviors from CBRS and MBRS, social-emotional functioning from ITSEA and TABS. | One-hr/week center based tx and approx. 2.5 hr/day in-home parent based tx in RT. Tx lasted for a mean of 11.4 months and focused on reciprocity, contingency, shared control, affect, and matching pace during daily routines. | Sig increases in maternal responsiveness (35%) and affect (27%) for 80% of mothers. Increased responsivity associated with improvements in children's social-emotional functioning (incl. engagement, cooperation, joint attention, and affect). | Type 3 study – RCT – Blind assessment – Incl/excl criteria – Standardized dx battery – Comparison group + Tx fidelity + Tx manual Other: Pre–post design. |
| Mahoney & Perales (2005) | 20 children with PDDNOS (M CA 32 months), 30 children with other DDs (M CA 23 months), overall 62% males. M CA of mothers 33 years, 89% Caucasian, 93% married. | Developmental Rainbow, TBPA, Videotaped samples of mother-child interactive behaviors from CBRS and MRBS, social-emotional functioning from ITSEA and TABS. | Weekly 1-hr parent–child sessions either at center or in-home by early intervention specialist over course of 1 year (M 11 months). Average of 15 hr/week of parent-reported implementation. Tx focused on pivotal developmental behaviors related to cognitive, communication, and socio-emotional functioning and influenced by maternal responsiveness. | Sig increase in maternal responsivity and in children's communication, cognitive, and socio-emotional functioning, greater developmental gains for PDDNOS group. Group diff related to degree of maternal responsivity. | Type 3 study – RCT – Blind assessment – Incl/excl criteria – Standardized dx battery – Comparison group + Tx fidelity + Tx manual. Other: Pre-post design. |
| Moes & Frea (2002) | 3 children with autism (M CA 41 months) with severe disruptive behaviors. No other information provided. | % of 10-sec intervals with problem behaviors, intervals with functional communication, and an index of tx package's fit with family context. | In-home parent-implemented functional assessment and functional communication training. 1–2 days/week training sessions, with follow-up at 2-month intervals for 1 year after training completed. | Contextualized FCT within family's routines decreased problem behavior and increased functional communication and moderate scores in parents’ ratings of sustainability with tx package. | Type 2 study – RCT – Blind assessment + Incl/excl criteria – Standardized dx battery – Comparison group + Tx fidelitiy + Tx manual. Other: Single-subject design with 3 cases. Careful assessment. Maintenance and generalization data. |
| Sallows & Graupner (2005) | 23 children with autism randomly assigned to clinic-directed (N = 13, 11 male, M CA 33 months at pre-tx) or parent-directed group (N = 10, 8 male, mean CA 34 months at pre-tx). Median income per group provided. | ADI-R, BSID-II, CBC, CELF-III, ELM, Personality Inventory for Children, Reynell, Vineland, WISC-III or WPPSI-R, Woodcock-Johnson, classroom placement, therapeutic services. | Both groups received Lovaas tx. Clinic directed received mean of 39 hr/week for Year 1 and 37 hr/week for Year 2, 6–10 hr/week of in-home supervision, and weekly consultation. Parent directed received M of 32 hr/week for Year 1 and 31 hr/week for Year 2, 6 hr/month of in-home supervision, and consultation every 2 months. | Similar outcomes across measures for both groups (48%). Tx outcome best predicted by pre-tx imitation, language, and social responsiveness. | Type 1 study + RCT + Blind assessment + Incl/excl criteria + Standardized dx battery + Comparison group + Tx fidelity + Tx manual. |
| Salt et al. (2002) | 12 children dx with autism in exp group, M CA 42 months, MA 17 months. Received approx. 15 hr per week of other tx. Comparison group, M CA 38 months, M MA 21 months, received approx 20 hr per week of other tx. Sig higher IQ than exper group (56/39). All children Caucasian except 1, even distribution of SES. | ECSC, MCDI, PSI, PVCS, Symbolic Play Test 2nd ed., Vineland. | Exp group: parent-delivered developmental, naturalistic based tx focused on imitation, joint attention, language, social reciprocity, and play. Comp group: Waitlist for services, primarily speech and language therapy. | Exp. group improved sig on imitation measure, joint attn and social interaction from ECSC, and all the Vineland scales except communication. No diff in parent measures. Outcome on language measures not reported. | Type 3 study – RCT + Blind assessment – Incl/excl criteria – Standardized dx battery + Comparison group – Tx fidelity – Tx manual. |
| Sheinkopf & Siegel (1998) | 11 children in exp. tx group (M CA 34 months), 11 children in control group (M CA 35 months). Groups matched on CA, MA, dx (AD vs. PDDNOS), length of tx. No other information provided. | BSID-II, Cattell, DSM–III–R symptom severity, Merrill-Palmer, WPSSI. | Exp. tx: home-based parent-implemented Lovaas tx. for approx. 16 months with community based clinicians, average of 6 hr/week school-based services and 1 hour/week OT, ST. Control group: average of 10 hr/week school-based and 45 min./week OT, ST. | Exp. group scored sig higher IQ (difference about 25 points). Smaller sig effect on symptom severity but exp group still met dx criteria for autism or PDDNOS. | Type 3 study – RCT + Blind assessment – Incl/excl criteria – Standardized dx battery + Comparison group – Tx fidelity – Tx manual. Other: Dx does not use gold standard tools. Retrospective, outcome measures very limited. Analysis is clear. |
| Sherer & Schreibman (2005) | 6 children with autism: 3 responders to tx (2 male, M CA 39 months), 3 nonresponders to tx (2 male, M CA 50 months). 1 child from each group matched on language, age, IQ. | Pre-, post- and follow-up data on BSID-II or DAS, CARS, EOWPVT, Leiter, PPVT-R, Vineland, videotaped samples (four 5-min samples) on language, play (functional, symbolic, varied), and social-behavioral interaction. | 90 min of clinician-based 1:1 PRT (i.e., behavioral naturalistic tx) 4–5 times/week for 6 months for responders and 5 months for nonresponders. Limited follow-up data. | Responders improved in language, play, and social skills and generalized gains to untrained environments and stimuli vs. no change in nonresponders. Responders had more functional play, stereotypic language, and less avoidance behaviors. | Type 2 study – RCT – Blind assessment – Incl/excl criteria + Standardized dx battery + Comparison group + Tx fidelity + Tx manual. Other: Comparative design. Strong single-subject design with 3 ss in each group. Maintenance and generalization data. |
| Smith, Buch, & Gamby (2000) | 6 children dx with AD or PDDNOS (M CA 36 months, M IQ 50). No other information provided. | Pre-tx and once/month during first 5 months of tx, data on ELM. Pre-tx and 2–3 year follow-up on BSID-II or WPPSI-R, Reynell, Vineland. Retrospective parent-report of therapy hours. PSI at 3 months and follow-up. | Parents and therapists attended six 1-day training workshops in Lovaas model over 3 months in child's home for 6 hr. | 5 of 6 children showed rapid acquisition of learning skills but only 2 made gains on standardized tests at 2–3 year follow-up. Therapists in parent-run programs implemented correct tx procedures but less consistent than lab-based therapists. High parental satisfaction with in-home tx. | Type 3 study – RCT + Blind assessment + Incl/excl criteria – Standardized dx battery – Comparison group + Tx fidelity + Tx manual. Other: Descriptive study of outcomes of 6 Ss receiving a home-based model. |
| Smith, Groen, & Wynn (2000) | 28 children (M CA 36 months & IQ 51 months) randomized to intensive tx group (N = 15; 12 male, 7 autism,8 PDDNOS) or to parent training group (N = 13; 11 male, 7 autism, 6 PDDNOS).14 Caucasian, 6 Hispanic, 4 African American, 4 Asian. | Pre-tx, follow-up (CA of 7–8 years) data on BSID-II or S-B, Merrill-Palmer, Reynell, Vineland. Follow-up measures of WIAT, social-emotional functioning from CBC and Teacher Report Form, Family Satisfaction Questionnaire, class placement, first 4 months of tx, assessed progress from ELM. | Intensive tx group received 30 hr/week of discrete trial format for 2–3 years in teams of 4–6 student therapists with 5 hr/week of parent-implemented tx for first 3 months of tx. Initial 1:1 instruction implemented in children's home with gradual transitions to classroom settings. Parent training group received two sessions/week in homes for 3–9 months and implemented an additional 5 hr/week of independent instruction. Parents taught discrimination learning, discrete trial formats, and functional analyses. | Intensive tx group showed sig diff in IQ, visual-spatial skills, language development, academic achievement and had less restrictive school placement, no group diff in mean Vineland scores and on standardized tests of behavior problems. Between group diff in follow-up IQ were about half that reported by McEachin et al. (16 vs. 31 points), as well as in the proportion of children placed in regular classes without special services (27% vs. 47%). | Type 1 study + RCT + Blind assessment + Incl/excl criteria + Standardized dx battery + Comparison group + Tx fidelity + Tx manual. Other: Clearly described analytic approach. |
| Stahmer & Ingersoll (2004) | 20 children with ASD (16 male, M CA at start 28 months, mean time enrolled 10 months). 90% married, 60% Caucasian, 10% Asian, 10% Filipino, 20% Hispanic. | Data on BSID-II, GARS, Vineland, behavioral evaluation to determine functional skill level at program entry and exit. | CTS inclusive program includes incidental and other evidence-based teaching techniques (e.g., PRT, discrete trial, PECS, modified sign language) for 3 hr/day, 5 days/week; 2 hr/week of individualized special skills training; and weekly 2-hr home visits for parent training with 10 hr/week of parent-implemented tx. Teacher-to-child ratio (1:3), autism to typical development ratio (8:8). | Sig increases on standardized assessments (37% functioning in typical range at exit vs. 11% at entry), in functional communication skills (90% at exit vs. 50% at entry), and social and play behaviors. | Type 3 study – RCT – Blind assessment + Incl/excl criteria + Standardized dx battery – Comparison group + Tx fidelity + Tx manual. Other: Pre-post design. No control for maturation. |
| Stoelb et al. (2004) | 19 children dx with autism (14 male, mean CA 55 months), wide range of SES and parent participation in tx. 6 with abnormal brain structure, 11 with regression, 5 were macrocephalic, 2 were microcephalic, 13 with sleep difficulties. | Medical assessment (MRI, EEG, morphologic measurements, dermatoglyphic analysis, skin tests, parent interviews), pre-tx functioning, 4-point scale of parental involvement, tx intensity. | In-home therapist-based discrete training, weekly phone monitoring, and supervisory workshops every 2 months. | Physical dysmorphology sig predicted tx change (58% of variance in change scores over 6 months, 67% over tx year) and language acquisition for 90% of nonverbal children. Age at onset of tx predicted greater gains vs. history of regression predicted poorer gains. | Type 3 study – RCT – Blind assessment + Incl/excl criteria – Standardized dx battery – Comparison group – Tx fidelity – Tx manual. Other: Retrospective design. No standard tx. |
| Takeuchi et al. (2002) | 8 children dx with autism (7 boys, mean CA 63 months). All English-speaking families living in Malaysia. | One pre- and post-tx direct observation of % of correct responses, categories of rewards, and social validity measure of quality of child-trainer interaction. Parent questionnaire. | Nine 20-min supervising sessions for parent-implemented Lovaas tx in 3 days. Parents received feedback in selecting appropriate tasks, using strategies to minimize learning errors, and presenting a variety of rewards. | Supervision increased children's correct response rates and variety of rewards. | Type 6 study – RCT – Blind assessment – Incl/excl criteria – Standardized dx battery – Comparison group + Tx fidelity + Tx manual. Other: Similar to a case report. No outcome data presented. |
Note: dx = diagnosis; AD = Autistic Disorder; tx = treatment; + = present in the study; – = absent in the study; ADOS = Autism Diagnostic Observation Schedule; PSI = Parenting Stress Index; RCT = randomized controlled trial; Incl/excl = inclusion/exclusion; ASD = ; CA = chronological age; BSID–II = Bayley Scales of Infant Development, 2nd edition; BAS = British Ability Scales; Griffiths = Griffiths Scale of Infant Development; WISC-III (or WISC-R) = Wechsler Intelligence Scale for Children, 3rd edition; WPPSI-R (or WPPSI) = Wechsler Preschool and Primary Scales of Intelligence Revised; Reynell =Reynell Developmental Language Scales 3rd UK edition; Merrill-Palmer = Merrill Palmer Scales of Mental Tests; EIBT = Early Intensive Behavioral Treatment; ADI–R = Autism Diagnostic Interview–Revised; VABS (Vineland) = Vineland Vineland Adaptive Behavior Scales; SES = socioeconomic status; MCDI = MacArthur Communicative Developmental Inventory; NVIQ = nonverbal intelligence; ABA = Applied Behavior Analysis; diff = difference; sig = significant; PDDNOS = Pervasive Developmental Disorder Not Otherwise Specified; IBT = Intensive Behavior Therapy; AP = Comparison group; GP = Comparison group; DP-II = Developmental Profile-II; S-B = Stanford-Binet Intelligence Scale, 4th edition; PECS = Picture Exchange Communication System; SIT = Sensory integration therapy; exp = experimental; CARS = Childhood Autism Rating Scale; EIDP = Early Intervention Developmental Profile; PSDP = Preschool Developmental Profile; TAQ = TRE-ADD Autism Quiz; PRT = Pivotal Response Training; ELAP = Early Learning Accomplishments Profile; LAP = Learning Learning Accomplishments Profile; CBRS = Child Behavior Rating Scale; MBRS = Maternal Behavior Rating Scale; ITSEA = Infant Toddler Social Emotional Assessment; TABS = Temperament and Atypical Behavior Scale; DD = Developmentally disabled; TBPA = Transdisciplinary Play-Based Assessment; FCT = Functional Communication Training; CBC = Child Behavior Checklist; CELF III = Clinical Evaluation of Language Fundamentals, 3rd edition; ELM = Early Learning Measure; Woodcock-Johnson = Woodcock-Johnson III Tests of Achievement; MA = Mental Age; ESCS = Early Social Communication Scales; MCDI = MacArthur Communicative Developmental Inventory; PVCS = Preverbal Communication Schedule; Cattell = Cattell Infant Intelligence Scale; DSM–III–R = Diagnostic and Statistical Manual of Mental Disorders-Revised (3rd ed.); DAS = Differential Abilities Scale; EOWPVT = Expressive One-Word Picture Vocabulary Test; Leiter = Leiter International Performance Scale; PPVT-R = Peabody Picture Vocabulary Test-Revised; WIAT = Wechsler Individual Achievement Test; GARS = Gilliam Autism Rating Scale; CTS = Children's Toddler School.