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ORIGINAL ARTICLE
Meta-analysis of Research on Sensory IntegrationTherapy for Individuals with Developmentaland Learning Disabilities
Han Ming Leong & Mark Carter &
Jennifer R. Stephenson
Published online: 29 October 2014# Springer Science+Business Media New York 2014
Abstract Sensory integration therapy (SIT) is a widely used intervention for peoplewith disabilities to address educationally related outcomes and has been subject toongoing controversy. The outcomes from 30 comparison group studies on sensoryintegration therapy for people with, or at-risk of, a developmental or learning disability,disorder, or delay were reviewed and analyzed. Studies comparing SIT to no treatmentyielded a statistically significant but small effect. However, when SITwas compared toalternative interventions, differences were non-significant. Numerous methodologicalflaws were identified, such as issues in clearly defining treatment and evaluatingintegrity, poor quality of research, and diversity of outcome measures. There was littleevidence that SIT was an effective intervention for any diagnostic group, particularlywhen functional blinded outcome measures were examined. Minimum methodologicalrequirements for any future research studies are discussed.
Keywords Sensory integration therapy . Outcome studies . Developmental disabilities .
Meta-analysis . Evidence-based practice
Ayres (1972b) proposed that children with learning disorders may have neurologicalproblems related to processing sensory information, referred to as a sensory integrationdysfunction, otherwise known as a sensory processing disorder using current nosologyproposed by Miller, Anzalone, Lane, Cermak, and Osten (2007). Ayres suggested thataddressing sensory integration dysfunction could lead to gains in higher order learning
J Dev Phys Disabil (2015) 27:183–206DOI 10.1007/s10882-014-9408-y
H. M. Leong (*) :M. Carter : J. R. StephensonMacquarie University Special Education Centre, Institute of Early Childhood, Macquarie University,Sydney, NSW 2109, Australiae-mail: [email protected]
M. Cartere-mail: [email protected]
J. R. Stephensone-mail: [email protected]
skills, such as language (Ayres and Mailloux 1981), academic skills such as readingand writing (Ayres 1972a), and motor coordination (Ayres 1977). These skills werebelieved to be related to the neurological systems that integrate sensory information(Ayres 1972b).
In order to address the theorized sensory processing issues of children with learningdisabilities, Ayres developed an intervention called sensory integration therapy (SIT).SIT involves the provision of controlled sensory stimulation. The student’s desiredresponse to the therapy is called an adaptive response, which is thought to be animportant indicator of successful integration of the sensory system (Ayres 1972b). Asthe implicit aim of SIT is to alter the way that the brain organizes and processessensation, SIT was proposed to be particularly effective for younger children whoseyoung brains have higher plasticity and are still in the process of forming neuralconnections (Ayres 1972b).
Classic SIT, as the term is used in this paper, refers to the delivery of intervention ina dedicated individual or small group session. A typical classic SIT session wouldinvolve the provision of various forms of sensory stimulation, such as being rubbedwith brushes or other textured items, being swung or spun in a hammock, being rockedback and forth while lying on a gym ball, movement while lying on a scooter board,and joint compression from wrist weights. Different practices, interpretations andtheories related to the sensory integration framework have been explored since itsconception (Pollock 2009). Some examples of associated practices include the sensorydiet where sensory-based activities are scheduled for the individual at home and inschool (Baranek 2002), the Wilbarger Protocol which involves a brushing componentand joint compression as well as the sensory diet (Wilbarger and Wilbarger 1991), anduse of weighted vests (Olson and Moulton 2004).
There have been some efforts to develop a fidelity instrument that identifies essentialintervention components of SIT (Parham, Roley, Mailloux, Koomar, and Bodison 2011;Parham, Roley, May-Benson, et al. 2011). Parham et al. (2007) found that most of thestudies reviewed did not adhere (or report adherence) to the intervention componentsoutlined in their instrument. The term Ayres Sensory Integration® has been trademarked,and refers to the intervention strategies which adhere to core principles of Ayres’ originalframework (Smith Roley, Mailloux, Miller-Kuhanek, and Glennon 2007).
Sensory integration has been widely employed as an intervention to address educa-tional outcomes. SIT is popular, being often used by occupational therapists. In asurvey of practices of occupational therapists in the United States by Case-Smith andMiller (1999), 95 % of the participants were reported to use sensory integration therapyat least sometimes for children with autism. Whereas SIT was initially advocated forchildren with learning disabilities (Ayres 1972b), its use has been explored for childrenwith a wide variety of difficulties including those with environmentally deprivedbackgrounds (Cermack 2001), developmental coordination disorder (Davidson andWilliams 2000), and severe trauma (Alers 2005). Recently, SIT appears to have becomea popular intervention for students with autism in particular (Goin-Kochel, Myers, andMackintosh 2007; Green et al. 2006; Hess, Morrier, Heflin, and Ivey 2008; Thomas,Morrissey, and McLaurin 2007).
Nevertheless, SIT is subject to ongoing controversy (Pollock 2009). There havebeen a number of descriptive reviews based on primary sources (Arendt, MacLean, andBaumeister 1988; Baranek 2002; Dawson and Watling 2000; Lang et al. 2012; Leong
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and Carter 2008; May-Benson and Koomar 2010; Smith, Mruzek, and Mozingo 2005),as well as integrative reviews examining primary sources and/or previous syntheses(e.g., American Association of Pediatrics 2001; Hoehn and Baumeister 1994; Hyatt,Stephenson, and Carter 2009; Maine Administrators of Services for Children withDisabilities 2000; Myers and Johnson 2007; National Autism Center 2009; NationalResearch Council (Ed.) 2001; Perry and Condillac 2003; Roberts, Prior, Rodger, andWilliams 2011; Simpson 2005; Williames and Erdie-Lalana 2009) but only twopublished meta-analyses (Ottenbacher 1982; Vargas and Camilli 1999). Although therehave been some dissenting opinions (e.g., May-Benson and Koomar 2010; Ottenbacher1982), the consensus of the majority of reviews is there is only weak evidence tosupport the use of SIT for people with disabilities.
May-Benson and Koomar (2010), although noting some caveats, provided a gener-ally positive assessment of the effects of SIT. Nevertheless, there were several signif-icant weaknesses in this review including the absence of reliability checks on articleselection and data extraction. Furthermore, May-Benson and Koomar (2010) primarilyused vote counting of statistically significant findings rather than a meta-analyticsynthesis of the studies examined. Another recent review by Lang et al. (2012) onclassic forms of SIT and various interventions related to SIT (including weighted vestsand sensory diets) for people with autism spectrum disorders reported mixed resultsoverall. Lang et al. concluded that many of the studies reviewed had serious method-ological flaws, and thus there was insufficient evidence from the studies reviewed tosupport the clinical use of SIT beyond research purposes. Case-Smith, Weaver, andFristad (2014) also reviewed studies of the effects of SIT in individuals with autism,noting that studies provided some evidence of positive effects on Goal AttainmentScaling and some behaviors related to sensory problems. Nevertheless, they highlightedthe limited evidence and the need for further high quality studies.
Of the two meta-analyses (Ottenbacher 1982; Vargas and Camilli 1999),Ottenbacher found early positive indications for the efficacy of SIT. Most of theresearch examined, however, suffered from poor quality design (Arendt et al. 1988),and this was not addressed in Ottenbacher’s review. In addition, Ottenbacher limited hisanalysis to studies with no treatment control groups and did not consider studies thatcompared SIT to alternative treatments. Ottenbacher’s positive results were not con-firmed when a more comprehensive meta-analysis of literature on SIT was conductedby Vargas and Camilli (1999). They reviewed 24 primary studies and found a smalleffect size (ES) of 0.29, with earlier studies having higher effect sizes and with ESapproximating zero in the most recent research examined. In addition, when SIT wascompared to alternative interventions, the ES of 0.09 was not significantly differentfrom zero. This most recent published meta-analysis on SIT (Vargas and Camilli 1999)is over a decade old. Furthermore, the existing analyses by Ottenbacher and by Vargasand Camilli have a number of potential sources of bias, including failure to performreliability checks on article selection and data extraction.
Considering the continued popularity of the intervention to address educationallyrelated outcomes, particularly for individuals with learning and developmental disabil-ities, there is a need for an updated comprehensive review of studies on the efficacy ofSIT. The present study presents a meta-analysis of research examining SIT whichincluded at least one comparison group and where the participants were people with,or at-risk of, a learning or developmental disability, disorder, or delay.
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Method
Identification and Screening
A literature search was conducted in August 2010 in the ERIC, A+Education,Psycinfo, CINAHL, and MEDLINE databases using the search terms “sensoryintegrat*”, “Wilbarger Protocol”, “sensory diet” and “weighted vest*”, where “*”represents truncation, limited to English language and to research studies where thosesearch options were available. A summary of the article selection and screeningprocess, including interrater reliability, is provided in Fig. 1. Interrater agreement wascalculated by dividing the number of studies agreed to be included or excluded by thetotal number of studies. Abstracts were then examined by the first author and either thesecond or third author to determine if the studies examined the effects of SIT (orspecific related interventions including sensory diet, Wilbarger Protocol, and weightedvests) and also reported empirical outcome data for participants. The full texts of thesepapers were then obtained for further review. In addition, 11 studies not previouslyfound through the database search were identified from a review of the reference lists offive major reviews on SIT (Baranek 2002; Dawson and Watling 2000; May-Bensonand Koomar 2010; Ottenbacher 1982; Vargas and Camilli 1999), and the full text ofthese articles was also obtained for further review.
Full text articles were then examined in two stages by two authors to determineeligibility for inclusion. For the preliminary stage, studies were included if the studyreported empirical outcomes for participants and classic forms of SIT were used.Classic forms of SIT were considered to be group or individual sensory based inter-ventions identified as SIT by the study authors based on Ayres’ theoretical framework.Studies using related procedures, such as sensory diets, in addition to classic sensoryintegration therapy, were not excluded at this stage. The remaining studies weresystematically reviewed in the next stage where they were included if they employedcomparison group designs and reported outcomes of the use of only classic SIT forparticipants who had, or were at-risk of, a developmental or learning disability,disorder, or delay. Two notable exclusions were articles where the authors claimed touse sensory integration therapy but used virtual reality-based therapy (Jung, Lee, andLee 2006) and Belgau-board-based therapy (Meyers and Schkade 1992) instead, ratherthan a form of sensory integration therapy. The review authors unanimously agreed thatthese studies were not appropriate for inclusion. The studies remaining after bothscreening processes were used in the final coding process. Disagreements were re-solved through discussion amongst all authors.
During the coding stage where the studies were examined in greater detail (seebelow), 14 studies were excluded for a variety of reasons such as having insufficientinformation to calculate the ES (Cabay, King, and Wojten 1999; Clark, Miller, Thomas,Kucherawy, and Azen 1978; DeGangi, Wietlisbach, Goodin, and Scheiner 1993;Dunbar, Carr-Hertel, Lieberman, Perez, and Ricks 2012; McKibbin 1973; Paul et al.2003; Tew 1984), having no appropriate control elements present even though a groupdesign was employed (Bundy, Shia, Qi, and Miller 2007; Fallon, Mauer, and Neukirch1994; Piravej, Tangtrongchitr, Chandarasiri, Paothong, and Sukprasong 2009), orpresenting reanalysis of earlier studies (Kaplan, Polatajko, Wilson, and Faris 1993;Law, Polatajko, Schaffer, Miller, and Macnab 1991). In the case of one recent paper
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Fig. 1 Search strategy and screening process
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(Pfeiffer, Koenig, Kinnealey, Sheppard, and Henderson 2011), the lead author wascontacted and provided additional data to assist in calculation of effect sizes. The articleby Wuang, Wang, Huang, and Su (2009) was excluded owing to anomalies in the datapresented. Most of the post-test standard error data (from which standard deviation canbe calculated) reported in Wuang et al. (2009) were substantially lower than thecorresponding pretest data, in some cases up to 20 times lower. In addition, all thestandard errors at post-test were identical for each outcome measure (and reported toonly one decimal place). The authors provided ESs for control-treatment group differ-ences that did not appear to match those calculated from the data provided. We wereunable to clarify these issues with the authors, and given these inconsistencies, thepaper was excluded from analysis.
Coding and Data Extraction
Studies were coded according to the presence or absence of general features of SIT:explicit description of intervention as SIT; reference to Ayres theory; use of dedicatedSIT sessions; provision of explicit description of vestibular, tactile, and proprioceptivestimulation; explicit reference to other forms of sensory stimulation (e.g., olfactory);use of other interventions in conjunction with classic SIT (sensory diets; weightedvests; Wilbarger Protocol); and use of other SIT based strategies as per Table 4. Thepresence or absence of ten process elements identified in the instrument developed byParham and colleagues (Parham, Roley, Mailloux, et al. 2011; Parham, Roley, May-Benson, et al. 2011) was coded in relation to whether the program was clearly deliveredentirely by occupational therapists and if so, whether these therapists were reported tohave training in SIT. The presence of procedural reliability measures (manualizedtreatment, informal procedural reliability checks without data, or formal checks withdata) was coded. Where authors indicated that a published treatment manual wasavailable (Miller, Coll, and Schoen 2007), it was obtained and used to evaluate theintervention used in the study. Where it was indicated that an unpublished treatmentmanual was available from the authors, an attempt was made to obtain it from thecorresponding authors. Some study authors referred to general volumes such as Ayres(1972b) and Bundy, Lane, and Murray (2002) for details of intervention. The broadnature of these sources was such that it was impossible to determine specific interven-tion procedures in a given study with any degree of operational precision so thesesources were not considered in evaluating treatment characteristics.
Participant details were coded including numbers of participants; age; and numbersof participants with learning disabilities, intellectual disability, pervasive developmentaldisabilities, and other disabilities. Inclusion criteria used in the selection of participantswere coded against the following criteria: evidence of sensory integrative dysfunctionbased on a test or scale such as the Southern California Sensory Integration Tests(SCSIT) (Ayres 1980) or Short Sensory Profile (SSP) (Dunn 1999); evidence ofsensory integrative dysfunction based only on clinical opinion; presence of sensoryseeking behavior; presence of sensory avoiding behavior; presence of challengingbehavior (stereotypy, self-injurious behavior); absence of functional behavior (devel-opmental delay, poor attending behavior, skill deficits); and selection based on adiagnostic category only (e.g., participants included only because they were diagnosedwith autism spectrum disorders, learning disability, etc.).
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The presence of outcomes in three basic areas were initially coded:
(1) Sensory integration and perceptual-motor measures. Such measures are closelyrelated to sensory integration functioning or purported underlying constructs (e.g.,SCSIT, SSP, Southern California Postrotary Nystagmus Test [Ayres 1975]), andrelated perceptual and motor skills (fine, gross, etc.).
(2) Short-term functional measures. These measures described short-term (up to 2 h postintervention) behavioral changes including attention and challenging behavior.
(3) Long-term functional measures. These measures addressed changes in functionalskills, adaptive, or challenging behavior (e.g., academic performance, long-termchange in challenging behavior, on-task behavior.).
Given the nature of the activities described in SIT programs, it is plausible thatimprovement in aspects of sensory integration and perceptual-motor measures are causedby practice effects and may not be indicative of improved functional outcomes. Changes inshort-term functional measures may not be indicative of a change in underlying neurolog-ical processing unless long-term functional change also occurs. Changes in long-termfunctional skills that were clearly attributable to sensory integration therapy would beconsistent with the proposition that changes had occurred in underlying neurologicalprocesses. So of the three measurement outcome areas above, changes in long-termfunctional measures would give the greatest prima facie support to Ayres’ theoreticalframework and, thus, it was important to distinguish such changes from the other two areas.
The presence or absence of four forms of assessment used in each article was thencoded: direct elicited test of participant performance; observational assessment bytherapist or researcher; observational assessment by third party (e.g., behavior scaleor sensory profile completed by parent); and Goal Attainment Scaling.
Studies were coded according to whether they included a non-treatment group and/or an alternative treatment group, for the treatment duration, and the frequency andlength of treatment sessions. Finally, studies were rated against the four key qualitycriteria for group designs described in Table 1. Randomization, blinding, and attritionare extremely common key quality criteria in assessing studies involving group com-parisons (see Gersten et al. 2005; Higgins and Green 2011; United States Departmentof Education 2003; What Works Clearinghouse 2011). Establishing pretest equivalenceis of importance in studies examining educationally related interventions, as group sizestend to be relatively small and even with randomization, there is often significant risk ofnon-equivalence. One study that was examined (Reilly, Nelson, and Bundy 1983) useda within-subjects design (i.e., participants were subject to both interventions), so pre-test equivalence was not relevant and therefore full points were awarded (Table 2).
All articles were independently coded by the first and second authors for the dataextraction. Disagreements were resolved through discussion between all authors. Overallreliability for the data extraction was a mean of 88.7% with a range of 76.6% to 94.9%.
Data Analysis
The choice of standardization metric can have a significant impact on the calculated ES(McGaw and Glass 1980). Hedges’ g was used here to calculate ESs to adjust for smallsample bias. Hedges’ g standardizes by pooled post-test standard deviation. Apart from
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common usage, post-test standard deviation has the advantage that it can usually be derivedor estimated from other statistical data (McGaw and Glass 1980). It should be noted thatcombining ESs based on post-test standard deviations and the standard deviation of changescores is inappropriate as these ESs are standardized by different metrics.
Data were analyzed using the Comprehensive Meta-analysis program (Borenstein,Hedges, Higgins, and Rothstein 2005). In calculating ES, the expected direction ofchange on the measure was first determined and positive values were allocated to ESsthat reflected better performance in the SIT group. Where available, ES was calculatedusing pre- and post-test means and pooled post-test standard deviation data. In anumber of instances only standard deviations of pre- to post-test change scores were
Table 1 Quality criteria for evaluating studies
Characteristic Criteria Numberofstudies
Randomization 2 points: Participants are randomized to groups using an acceptablemethod (e.g., random number table, coin tossing).
2
1 Point: Claim participants are randomized but method not detailed. 15
0 points: Participants not randomly allocated to groups or allocated usinginappropriate method (e.g., by date of referral, birth date).
13
Blinding 2 points: Assessors were blind to group allocation on all measures. 8
1 point: Assessors were blind to group allocation on some (but not all) measures. 3
0 points: Assessors were not blind to group allocation. 19
Attrition 2 Points: Differential attrition was within 10 % for all study groups. 19
0 points: Differential attrition was not within 10 % for all study groups 11
Pre-testEquivalence
2 points: Groups were demonstrated to be statistically equivalent at pre-teston all outcome measures (or statistical adjustments made for differences).
13
1 point: Groups were demonstrated to be statistically equivalent at pre-test onsome outcome measures (or statistical adjustments made for differences).
3
0 points: Pre-test equivalence not examined or differences were unadjusted. 14
Table 2 Process elements of intervention used in studies
Process element Number of studies
Ensures physical safety 2
Presents sensory opportunities 20
Helps the child to attain and maintain appropriate levels of alertness 7
Challenges postural, ocular, oral, or bilateral motor control 12
Challenges praxis and organization of behavior 5
Collaborates in activity choice 8
Tailors activity to present just-right challenge 12
Ensures that activities are successful 12
Supports child’s intrinsic motivation to play 5
Establishes a therapeutic alliance 6
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provided. Post-test standard deviations can be derived from such data, as long ascorrelations between pre- and post-test scores are provided. None of the studiesexamined provided such data so correlations were estimated from published test-retest reliability coefficients. In a small number of cases (21 ES calculations) therewere no standardization data on particular assessments, so sensitivity analysis wasconducted using a plausible range of reliability coefficients (0.60 to 0.99). This range ofvalues only resulted in an overall change in the ES of less than 0.015 for no treatment(NT) and alternative treatment (ALT) comparisons, so a mid-range value of 0.80 wasemployed in the analysis. Where means and standard deviations were not provided,ESs were also derived from dichotomous data (events and/or non-events), and t valuesfor continuous data. In the absence of other data, estimates from p values for compar-isons between groups and participant numbers were used. ESs were calculated for eachoutcome variable, time point, and subgroup within a study. Because the calculation ofsynthetic ES was impractical given the large number of outcome variables and un-known correlations between these outcomes, mean ESs were calculated across outcomevariables and time points. Thus, confidence intervals are likely to be conservative.
Given the diverse nature of both the population examined and outcome measures, ana priori decision was made to employ a random effects analysis, consistent with therecommendation of Borenstein, Hedges, Higgins, and Rothstein (2009). Separateanalyses were initially conducted for NT and ALT comparisons. Further exploratoryanalyses were conducted for diagnostic group, study quality, study blinding status, typeof outcome measure, practitioner training and treatment integrity, combined or isolateduse of SIT, and year of publication.
Results
Some data sets were reported in more than one article (Ayres 1971, 1972a; Grimwood,and Rutherford 1981, and White 1979; Humphries, Snider, and McDougall 1993, andHumphries, Wright, Snider, and McDougall 1992; Salokorpi, et al. 1998, andSalokorpi, Rautio, Kajantie, and Von Wendt 2002; Wilson, Kaplan, Fellowes, Gruchy,and Faris 1992, and Wilson and Kaplan 1994). Ayres (1971) did not provide additionalinformation. These sets of articles were considered to be five single studies for thepurposes of the analysis. Thus, 30 studies that were reported in 35 different articlesfrom 1972 to 2013 were included.
There were a total of 967 participants in comparisons of SIT with no interventiongroups and 621 participants in comparisons with alternative treatment groups. Furtherinformation on the participants in each study is presented in Table 3. The minordiscrepancy between the group and total participant numbers resulted from anomaliesin the reporting in a small number of studies (Close, Carpenter, and Cibiri 1986;DePauw 1978; Roscoe 1987; Werry, Scaletti, and Mills 1990). Specifically, onlypost-test group numbers were provided in these studies and it could not be definitivelyestablished from which groups the reported attrition occurred. The mean interventionhours employed in the studies was 49.20 (SD 47.43, range 12–195). The mean numberof process elements (Parham, Roley, Mailloux, et al. 2011; Parham, Roley, May-Benson, et al. 2011) reported to be present in studies was 2.97 (SD 2.51, range 0–8)of a maximum of 10 (see Table 2). The mean quality score was 3.5 (SD 2.26, range 0–7)
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of a maximum of 8. Additional information on the studies is presented in Table 4. Atotal of 554 ESs were calculated, a mean of 18.5 per study.
NT and ALT Comparison Comparisons with NT groups were addressed in 21 studiesand 281 ES calculations and resolved to a fixed effect analysis (Q=18.61, p=0.55, I2=0.00). Hedges’ g for these comparisons was 0.18 (95 % CI, 0.03, 0.32), a small butstatistically significant effect (p=0.02). A forest plot of the relevant studies is providedin Fig. 2.
Comparisons involving alternative treatments involved 16 studies and 273 EScalculations and also resolved to a fixed effect analysis (Q=13.25, p=0.58, I2=0.00).Hedges’ g for these comparisons was 0.13 (95 % CI, −0.04, 0.31), which was notsignificant (p=0.14). A forest plot of the relevant studies is provided in Fig. 3.
Diagnostic Group Analyses for diagnostic groups are provided in Table 5 for NT andALT comparisons. Analysis was limited to studies where diagnostic groups could beisolated. Hedges’ g was small in most cases with only NT comparison for learningdisabilities approaching significance. The Q value was only significant for NT com-parisons for intellectual disabilities where I2 indicated that approximately 68 % ofobserved variance was due to heterogeneity among studies.
Study Quality Scores A comparison was made among the 23 studies with a qualityscore below six and the remaining seven studies with quality scores of six or above.The respective ESs were 0.14 (95 % CI, −0.01, 0.28) and 0.17 (95 % CI, −0.06, 0.40).Dichotomized study quality was not significantly related to ES (Q=0.05, df =1, p=0.83).
Study Blinding Status Blinding status of studies was also examined. The ES for the 19studies that were totally unblinded was 0.17 (95 % CI, −0.01, 0.33), for the threestudies that were blinded on some measures it was 0.07 (95 % CI, −0.25, 0.39), and forthe eight studies that were totally blinded it was 0.14 (95 % CI, −0.09, 0.37). Thesedifferences were not significant (Q=0.26, df =2, p=0.88).
Type of Outcome Variable Outcome variables related to sensory integration andperceptual-motor measures were examined in a total of 24 studies with Hedges’ g of
Table 3 Summary of participantfeatures
aNumber of studies is 18 due tonot all studies reporting numberof male and female participantsbNumber of studies is limited tostudies which provided ageranges
Number of participants
Participants
Total 1434
Malea 511
Femalea 181
Number of studiesb (n=21)
Participants aged 0–6 16
Participants aged 7–12 13
Participants aged 13–18 1
Participants aged 18+ 3
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Table 4 Summary of study features
Number of studies% (n)
General intervention features
Explicitly described as SIT 93.3 (28)
Ayres’ theories referenced 100 (30)
Dedicated SIT sessions 100 (30)
Vestibular stimulation 70.0 (21)
Tactile stimulation 70.0 (21)
Proprioceptive stimulation 56.7 (17)
Other stimulation 6.7 (2)
Other features (treatment group only) 17.7 (5)
Other intervention features
Sensory diet, explicitly described 0 (0)
Sensory diet, sensory stimulation in the context of activitiesembedded in the daily routine
3.3 (1)
Weighted vests 0 (0)
Wilbarger, brushing (correct locations) 0 (0)
Wilbarger, joint compression 0 (0)
Wilbarger, sensory diet 0 (0)
Other SIT-based 0 (0)
Structure
Training in sensory integration 16.7 (5)
Delivered by OT 46.7 (14)
Specific Procedural integrity measures
Manualized treatment 10.0 (3)
Informal procedural integrity checks without data 30.0 (9)
Formal procedural integrity checks with data 10.0 (3)
Outcomes
Sensory integration and perceptual motor measures 90.0 (27)
Short-term functional measures 3.3 (1)
Long-term functional measures 70.0 (21)
Form of assessment
Direct formal elicited testing of participant performance 96.7 (29)
Observational assessment of participant performance 23.3 (7)
Observational assessment by third party 40.0 (12)
Goal Attainment Scaling 10.0 (3)
Treatment inclusion criteria
Evidence of sensory integration dysfunction based on test or scale 43.3 (13)
Evidence of sensory integration dysfunction based on therapist clinical opinion only 3.3 (1)
Specific mentions of sensory seeking behaviors 0 (0)
Specific mentions of sensory avoiding behaviors 6.7 (2)
Presence of challenging behaviors 0 (0)
Absence of functional behaviors 10.70 (3)
Diagnostic category only 43.3 (13)
Design
No treatment control group 73.3 (22)
Alternative treatment group 53.3 (16)
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0.19 (95 % CI, 0.05, 0.34), which was significantly different from zero (p=0.02). Long-term functional measures were used in 20 studies with a resulting ES of 0.12 (95 % CI,−0.03, 0.26), which was not significant (p=0.12). Short-term functional measures wereonly used in a single study and the associated ES was −0.19 (95 % CI, −0.83, 0.46),which was not significant (p=0.57).
Fig. 2 Forest plot of Hedges’ g for comparisons with no treatment groups
Fig. 3 Forest plot of Hedges’ g for comparisons with alternative treatment groups
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Form of Assessment A small number of measures used a combination of methods for asingle measure and these were excluded from analysis. Direct elicited testing wasconducted in 24 studies resulting in an ES of 0.14 (95 % CI, −0.01, 0.29), whichwas not significantly different to zero (p=0.06). Direct observation was used in fourstudies with and ES of 0.03 (95 % CI, −0.31, 0.37), which was not significantlydifferent to zero (p=0.87). Observational assessment by a third party (excluding GoalAttainment Scaling) was employed in nine studies with an ES of 0.07 (95 % CI, −0.15,0.28), which was not significantly different to zero (p=0.53). Finally, in markedcontrast to the other results, Goal Attainment Scaling was used in three studies andthe resulting ES was 1.05 (95 % CI, 0.55, 1.54), which was significantly different fromzero (p<0.001).
Training and Treatment Integrity Several approaches were taken to evaluating theeffect of interventionist training and of treatment integrity on outcome. The ES forthe 25 studies that did not specify that interventionists had specific training in use ofSITwas 0.16 (95 % CI, 0.03, 0.29), compared with 0.09 (95 % CI, −0.19, 0.37), for the5 studies where interventionists were specified as trained. These differences were notsignificant (Q=0.17, df =1, p=0.67). The ES for the 14 studies that explicitly specifiedthat all intervention was delivered by an occupational therapist was 0.08 (95 % CI,−0.09, 0.25), compared with 0.21 (95 % CI, 0.04, 0.39) for the 16 studies where it wasnot stated that all intervention was delivered by an occupational therapist. Again, thesedifferences were not significant (Q=1.10, df =1, p=0.29). Finally the process elementscores ranged from 0 to 7 and studies with process scores below 4 were compared withthose process scores of 4 or above. The 18 studies with process scores below 4produced an ES of 0.13 (95 % CI, −0.02, 0.28) compared with 0.18 (95 % CI,−0.04, 0.40) for the remaining studies with 4 or above and these differences were notsignificant (Q=0.15, df =1, p=0.70).
Isolated and Combined Intervention Separate analyses were conducted for compari-sons involving the use of SIT alone as well as in combination with other interventions(e.g., neurodevelopmental therapy, Kephart). A total of 25 studies included at least one
Table 5 Summary of outcomes for diagnostic groups
Heterogeneity
Diagnostic Group Studies Ss Hedges’ g 95 % CI p Q p I2
NT Learning disabilities 9 588 0.18 −0.01, 0.37 0.07 4.13 0.85 0
Intellectual disabilities 3 81 0.45 −0.51, 1.41 0.36 6.33 0.04 68.42
Autism 1 32 0.29 −0.42, 1/00 0.42 NA NA NA
Other 8 491 0.14 −0.13, 0.42 0.30 7.75 0.36 9.64
ALT Learning disabilities 4 229 0.06 −0.25, 0.37 0.71 0.37 0.95 0.
Intellectual disabilities 5 204 0.24 −0.10, 0.58 0.17 4.11 0.39 2.60
Autism 2 55 −0.12 −0.59, 0.35 0.63 0.01 0.76 0
Other 5 272 0.28 −0.18, 0.75 0.23 6.57 0.16 39.14
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comparison where SIT was used in isolation with a resulting Hedges’ g of 0.13 (95 %CI, 0.03, 0.27), which was not significantly different from zero (p=0.05). Six studiesincluded comparisons where SIT was combined with another intervention with aresulting Hedges’ g of 0.16 (95 % CI, −0.15, 0.46), which was also not significantlydifferent from zero (p=0.32).
Year of Publication Studies were analyzed by period of publication. Where multiplepublications reported on the same data set, the first date of publication was used inanalysis. Pre 1982 publications yielded Hedges’ g of 0.33 (95 % CI, 0.10, 0.56), thosepublished between 1982 and 1994 yielded an ES of 0.05 (95 % CI, −0.12, 0.22) andthose published after 1994 and ES of 0.12 (95 % CI, −0.14, 0.38). These differenceswere not significant (Q=3.75, df =2, p=0.15). When analysis was limited to NTcomparisons, equivalent to the analysis of Ottenbacher (1982), a Hedges’ g of 0.41(95 % CI, 0.15, 0.67) resulted for studies prior to 1982, studies published between 1982and 1994 yielded an ES of 0.07 (95 % CI, −0.13, 0.27), and those published after 1994and ES of 0.07 (95 % CI, −0.26, 0.41). These differences were not significant (Q=4.57,df =2, p=0.10).
Publication Bias In order to assess possible publication bias, funnel plots were con-structed and the Duval and Tweedie trim and fill procedure was used to impute missingstudies. For both NT and ALT comparison, the resulting plots are presented in Figs. 4and 5 respectively. Three missing studies were imputed for the NTcomparison, with theadjusted ES reduced to a non-significant 0.12 (95 % CI, −0.04, 0.29). No missingstudies were imputed for the ALT comparisons. Orwin’s fail-safe N was not calculatedas ES point estimates for NT and ALT conditions were both already below aneducationally significant threshold of 0.2.
Hedges’ g
Fig. 4 Funnel plot of standard error by Hedges’ g for comparisons with no treatment groups. Note: Thereviewed studies are shown as open circles and the imputed studies shown as filled circles. The calculated ESis shown as an open diamond and the adjusted ES is shown as filled diamond
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Discussion
The current paper is the first meta-analytic review of group studies of the efficacy ofSIT in a decade. In this meta-analysis, quality indicators were systematically examined,procedures were taken to control for bias in article selection, treatment integrity wasexamined, and reliability checks were conducted on data extraction. Although thismeta-analysis reviewed more current studies, the results are consistent overall with theconsensus of earlier reviews on SIT, that the evidence for its efficacy is weak.Consistent with the result reported by Vargas and Camilli (1999), the current meta-analysis provided evidence that studies comparing SIT to no treatment yielded a smallbut statistically significant effect, but comparing SIT to an alternative interventionyielded a small and non-statistically significant difference. It should be noted, however,that the NT finding became non-significant with adjustment for publication bias.
Although the present overall results were consistent with those of Vargas andCamilli (1999), the analysis of historical NT data yielded some differences fromprevious analyses. Analysis of NT comparisons in the 1982–1994 period in the currentstudy resulted in an overall ES of 0.07, very similar to the 0.03 reported by Vargas andCamilli (1999). Analysis of the pre-1982 NT data, however, resulted in some differ-ences to previous studies. Specifically, Ottenbacher (1982) reported an ES of 0.79 forthese early studies, Vargas and Camilli (1999) reported an ES of 0.60, and the currentstudy produced a smaller ES of 0.41. There are a number of possible reasons for thesedifferences. First, each meta-analysis included a slightly different range of studies,depending on specific inclusion criteria. For example, Ottenbacher (1982) included thestudy of Clark et al. (1978), which upon examination appears to only present combinedpre-post data across the three treatment groups, rather than comparison between groups.In the current review, the study of Brody, Thomas, Brody, and Kucherawy (1977) wasincluded, which apparently reported on the same experiment. Vargas and Camilli(1999) also included Brody et al. (1977) in their meta-analysis. Ottenbacher (1982)also included some conventions that were not replicated in the subsequent meta-
Hedges’ g
Fig. 5 Funnel plot of standard error by Hedges’ g for comparisons with alternative treatment groups
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analyses such as adopting certain values when there were insufficient data to calculatean ES. For example, when a result was non-significant and there were insufficient datato calculate an ES, an ES of zero was assumed by Ottenbacher (1982). There were alsosome differences in the number of ESs calculated by Ottenbacher (1982). For example,Ayres (1978) presented a very complex and difficult to interpret analysis that includedcomparisons with a NT group as well as comparisons between treatment subgroupswithin the study. Although Ottenbacher (1982) reported an ES of 0.84 based on threeES calculations, we were only able to identify a single calculable ES with a resultingHedges’ g of 0.68. Finally and possibly most importantly, both the analyses of Vargasand Camilli (1999) and Ottenbacher (1982) reported no procedures for dealing withstudies that only presented gain score standard deviations. This suggests that theiranalyses included ESs that were standardized by a mixture of post-test and gain scorestandard deviations, effectively standardizing ES with different metrics. In contrast, inthe present study, post-test standard deviations were derived when they were missing inthe original articles and all ESs were standardized by post-test standard deviations.
There seemed to be little convincing evidence that SIT was effective for anyparticular diagnostic group or outcome measure. Overall, there were no significanteffects when data were analyzed by diagnostic group. Only no treatment comparisonsfor learning disabilities approached significance. When examining the outcomes of SITfor different types of measures separately, only sensory integration / perceptual-motormeasures (ES =0.19) was significant. Of particular importance is the finding that long-term functional outcome measures yielded only a small (0.12) and non-significant ES.This is important because the fundamental rationale for SIT is that it addressesneurological processing deficits that underlie performance of higher order skills. Failureto detect robust changes in functional skills raises questions regarding the basicrationale for the approach.
Direct testing, observational assessment by a clinician, and observational assessmentby a third party (such as a parent) all yielded small and non-significant effect sizes. Inmarked contrast, Goal Attainment Scaling yielded a large and significant ES (1.05) inthe three studies in which it was used. Although extensive justifications are offered forthe use of Goal Attainment Scaling (Pfeiffer et al. 2011; Schaaf et al. 2014) it is aninherently problematic measure. In particular, since parents are primarily the infor-mants, it is very difficult to effectively blind them. Pfeiffer et al. (2011) claimed thatparents were blinded to group allocation but given the reported communication level ofchildren, it would seem highly probable that information about the interventions couldbe communicated to parents. Thus, this claim could not be accepted without testing theblinding (i.e., asking parents which intervention they thought their children werereceiving). There is ample evidence that lack of blinding on subjective measures resultsin bias in reported outcomes of research (Hróbjartsson et al. 2012, 2013; Wood et al.2008). Data reported by Hodgetts, Magill-Evans, and Misiaszek (2011) for a sensoryintegration aligned intervention (weighted vests) indicated higher estimates of efficacywith unblinded subjective measures than blinded subjective or objective measures.Equally problematic is that Goal Attainment Scaling does not inherently involve thecollection of any specific or objective data on participant performance and relies onsubjective retrospective parental reports. Furthermore, a recent study of a sensoryintegration aligned therapy (weighted blankets) provided evidence of improvement insubjective non-blinded parent measures that was not supported by objective evidence
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(Gringras et al. 2014). Although Goal Attainment Scaling certainly has advantages interms of flexibility and ease of implementation and may be useful as a secondarymeasure, the above considerations should exclude it as a primary outcome measure.
There were a number of characteristics of the studies examined that both limit theinterpretability of the available data and have implications for future research on SIT.These will now be addressed.
Operationalization of Treatment and Evaluating Integrity Many descriptions of inter-ventions in the studies reviewed in this meta-analysis were very limited, and someelements that were often emphasized in early reports, such as inhibition of primitivepostural reflexes, were rarely mentioned in later research. Reviews or applications ofSIT that have not drawn supportive conclusions have often been criticized (e.g., Case-Smith and Schaaf 2012; Schaaf and Blanche 2011) for including studies that did notcorrectly or appropriately apply the intervention. Contributing to this problem is thatresearch examining SIT typically provides very limited descriptions of the intervention(Parham et al. 2007), making it very difficult to operationally determine the character-istics of the intervention employed. In some cases, descriptions literally amounted tolittle more than a statement that the intervention was implemented (e.g., Werry et al.1990). The issue is highlighted in the present review by the fact that only a mean of2.97 process elements of the 10 process elements outlined by Parham and colleagues(Parham, Roley, Mailloux, et al. 2011; Parham, Roley, May-Benson, et al. 2011) wereidentified in the contributing studies. It should be noted that this does not necessarilyindicate that these intervention features were absent, but rather that they were notadequately documented in published research. Given this state of affairs, a pragmaticapproach was taken in identifying studies in the current paper. Studies were accepted ifauthors self-identified an intervention as sensory integration therapy with reference to arelevant framework (e.g., Ayres 1972b), and where descriptions of the interventionwere consistent with classic SIT activities (Ayres 1972b).
There are two important implications of the severe and chronic deficiencies in thedescriptions of interventions in the SIT research. First, it places a degree of constrainton the interpretations of the present review. This is further complicated by the relatedlimited treatment integrity data with 10 % of studies providing manualized treatment,30 % reporting informal procedural integrity checks (without data), and 10 % providingformal evaluation with presentation of data. Second, it highlights the critical need for allfuture researchers to both clearly document key features of the intervention as well asinclude formal measures of treatment integrity. It is encouraging to note that recentstudies (e.g., Pfeiffer et al. 2011; Schaaf et al. 2014) have employed a version of theParham and colleagues instrument (Parham, Roley, Mailloux, et al. 2011; Parham,Roley, May-Benson, et al. 2011), which should remove questions about whetherintervention is appropriately described as sensory integration therapy.
Research Quality Arendt et al. (1988) criticized studies of the efficacy of SIT for thepoor quality of research designs used. More recently, methodological limitations in thecurrent literature base have been acknowledged (May-Benson and Koomar 2010), ashas the need for future high quality studies (Schaaf, Benevides, Kelly, and Mailloux-Maggio 2012). The findings of this meta-analysis indicate that the methodologicalcriticisms of Arendt et al. (1988) hold true when a broader sample of studies on the
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efficacy of SIT is examined. The mean quality score was 3.5, of a total of 8. The mostcommon weaknesses included lack of blinding, failure to establish pretest equivalence,and failure to randomize. Although researchers in 15 studies did claim randomization,most failed to document how randomization was conducted, so the risk of bias wasconsidered unclear (Higgins and Green 2011). This point may seem somewhat pedanticbut in most cases where an explicit description was provided of the randomizationprocess, the method described was unacceptable. For example, Uyanik, Bumin, andKayihan (2003) assigned participants into groups according to the date of admittance totheir clinic, a method that is considered unacceptable (Higgins and Green 2011). Roscoe(1987) randomly allocated classes to treatment but, immediately prior to treatment,reallocated two classes to the control group because the teachers were unable to continuewith the study, effectively invalidating the randomization of classes. Again, the excep-tions were the relatively recent studies (Pfeiffer et al. 2011; Schaaf et al. 2014).
Low quality pilot studies may be justified in the early stages of development of anintervention but research on SIT dates back 40 years, and therefore low quality studiesare no longer acceptable. The quality of research in the studies reviewed in this meta-analysis did not produce significantly different ES. Only a small number of studieswere of sufficient quality to allow any reasonable degree of confidence in conclusions(and these failed to produce convincing evidence of efficacy). The recent randomizedcontrolled study of Schaaf et al. (2014) showed substantial improvement in quality butwas substantially flawed by the use of Goal Attainment Scaling as a primary outcomemeasure, with its inherent problems with blinding and subjectivity, as previouslydiscussed.
Future studies using group designs should incorporate minimum standards ofrandom assignment with clear description of the randomization method, establishmentof pretest equivalence of groups (or application of appropriate statistical corrections),and, very critically, blinding of outcome measures. Studies that do not meet theseminimum criteria should not be considered for publication.
Multiple Outcomes Perhaps one of the most striking features of the research examinedis the diverse array of outcomes examined and, in many cases, the large number ofoutcome variables, sometimes without any attempt to correct for family-wise error. Themean number of codable outcomes for the meta-analysis was 18.5, and in some casesnon-significant outcome measures could not be included due to lack of sufficientinformation. For example, Humphries et al. (1992) reported a total of 108 differentoutcomes across NT and ALT comparisons, reporting three significant differences infavor of the SIT group. May-Benson and Koomar (2010) have suggested that with alarge number of outcome measures, correction for multiple comparisons (where ap-plied) may make it difficult to detect actual treatment differences. Possibly even moreproblematic, particularly given the frequent lack of correction for multiple compari-sons, is the risk of false positive findings reflecting random noise in these data.
One recent approach to addressing the issue of appropriate outcome measures is toscreen large numbers of instruments to determine which might be “sensitive” to theeffects of SIT (e.g., Miller, Coll, et al. 2007). Not only is such a shotgun approach likelyto throw up Type I errors (false positives), it is difficult to defend on conceptual grounds ifthe purpose of research is to evaluate whether SIT is effective, as opposed to seek supportfor a prior assumption that it is effective. Assuming the former, a more appropriate and
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defensible approach would be first to identify specific important and meaningful out-comes that would be theoretically expected with therapy. A second step would be to thenidentify the most defensible and appropriate measures of these outcomes.
In future research, there is a need to specify a reasonable number of primaryoutcomes a priori on theoretical and conceptual grounds. Furthermore, primacy shouldbe given to outcome measures that reflect practical and important change to partici-pants, and have sound psychometric properties. We would support the suggestion ofMay-Benson and Koomar (2010) that researchers should consider more functionaloutcome measures in SI research. We would not agree with Miller, Coll, et al. (2007),however, that Goal Attainment Scaling offers a desirable option due to the inherentproblem of blinding respondents (typically parents), and inherent subjectivity.
Participant Selection One notable feature of the research examined in this meta-analysis was the range of disabilities addressed and the extensive variation in inclusioncriteria. In approximately 43 % of studies, intervention was provided on the basis of adiagnostic classification with a further 43 % assessing sensory integration dysfunctionusing a formal test scale of some description. These latter groups varied considerably,with some researchers employing extensive screening and assessment for inclusion(e.g., Carte, Morrison, Sublett, Uemura, and Setrakian 1984; Miller, Coll, et al. 2007;Wilson and Kaplan 1994; Wilson et al. 1992). There appears to be no pragmaticagreement among researchers on the specific diagnostic indications and objectivecriteria to determine the appropriateness of SIT. Based on the research examined here,SIT appears to have been applied on the basis of largely open-ended indications andcriteria, and this creates obvious problems in interpreting the corpus of research. There isa present need to clearly define objective criteria for the application of the intervention.
Recommendations for Future Studies Despite several decades of research, there re-mains little evidence that SIT is effective for any diagnostic group. Interpretation ofresearch continues to be hampered by poor methodological quality, although it iscommendable that some recent studies (e.g., Schaaf et al. 2014) have improvedsubstantially. Based on the current analysis we would recommend several minimumcriteria for future group research studies in the area:
1. Random assignment to groups with explicit documentation of randomizationprocedures.
2. Blinding of all assessments.3. Establishing pre-test equivalence of groups (or statistical correction) with clear
documentation of attrition.4. Nomination of primary outcome variables a priori.5. Direct measurement of functional outcomes that are related to the theoretical basis
for the intervention and have adequate psychometric properties.6. Clear operational manualization of the intervention to allow replication.7. Direct measurement of treatment integrity.
There are a large number of exploratory and poor quality studies in the area of SI.Research that fails to meet these standards is unlikely to make any meaningfulcontribution to the literature and should not be considered for publication.
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Conclusion
Although there have been a number of new studies of the efficacy of SIT since the lastmajor systematic review a decade ago, the results of this meta-analysis also indicate thatevidence for the efficacy of SIT remains very weak. There was little evidence ofimprovements in functional outcome measures, and most of the studies revieweddemonstrated numerous methodological problems. Although widespread clinical ap-plication of SIT is acknowledged, in light of the present review it is difficult torecommend the use of SIT outside of the research context. It is recommended thatfuture research into SIT meets minimum methodological standards in order to beconsidered for publication.
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