Evaluating the Effectiveness of Hippotherapy on Social Functioning for Children with
Autism Spectrum Disorder
Caiti McDaniel MS, OTR/L
Beth Hoesly MS, OTR/L
Candy Tefertiller, PT, DPT, NCS
Katia Hannah, CPH
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Autism spectrum disorders (ASD) are a group of developmental disabilities characterized
by restricted or repetitive behaviors and deficits in communication and social interaction. The
Center for Disease Control and Prevention (CDC) estimates that one out of every 88 children
born in the United States today will be diagnosed with ASD (Center for Disease Control and
Prevention, 2012). This report also found that the prevalence rate rose by 78% from 2002 to
2008, and is estimated to continue rising. Therefore, more and more children and their families
are affected by this disorder every year. ASD has profound effects on the child’s development
and quality of life.
One particular area of development that is affected by autism is social functioning.
Children with ASD demonstrate impairments in social orientation and attentional distress—the
instincts to spontaneously pay attention to social stimuli and display sensitivity to another’s
emotional cues (Dawson et al., 2004). Additionally, young children with autism do not engage in
joint attention—defined as the sharing of attention with others through showing, pointing, and
coordinated looks between objects and people—as often as typically-developing children
(Charman et al., 1997). All of these deficits in social interaction skills have implications for the
child’s social participation. Preschool-aged children with ASD have been found to be less likely
to socially interact with their peers than typically-developing children (McGee, Feldman, &
Morrier, 1997). In a study evaluating teenagers with autism, the authors found that adolescents
with ASD were significantly more likely than their peers with other disabilities to be socially
isolated, never to see or get called by friends, and never to be invited to activities (Orsmond,
Shattuck, Cooper, Sterzing, & Anderson, 2013).
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While there is no cure for ASD, there is evidence that early intervention can decrease
symptoms and enable the child to thrive throughout the lifespan (e.g. Dawson & Osterling, 1997;
Karanth & Chandhok, 2013; Klintwall, Eldevik, & Eikeseth, 2013). Children with autism
typically receive a variety of therapeutic services to promote their health and well-being,
including: occupational therapy, physical therapy, speech-language therapy, and behavioral
therapy. These therapies typically take place within an outpatient medical environment, the
school environment, or in the home. One emerging therapeutic technique for children with
autism involves providing therapeutic services using a horse in an equine environment.
The American Hippotherapy Association (AHA) defines hippotherapy as “the
incorporation of equine movement by physical therapy, occupational therapy, or speech language
pathology professionals in treatment. These professionals use evidence-based practice and
clinical reasoning in the purposeful manipulation of equine movement to engage the
sensorimotor and neuromotor systems to create functional change in their patient” (AHA, 2015).
A recent study found that 11% of parents of children with an ASD report utilizing hippotherapy
or other equine interventions for their children (Thomas, Morrissey, & McLaurin, 2007).
Despite the growing use of hippotherapy, there is little evidence to support its beneficial
effect for children with autism. A systematic mapping review of 35 years of peer-reviewed
literature only located three articles that investigated the effects of hippotherapy specifically for
children with autism (Wood, McDaniel, & Hoesly, 2015). Using a single-subject design, Taylor
et al. (2009) demonstrated that 16 weeks of hippotherapy increased volition during play of three
children with autism. Similarly, Tabares et al. (2012) used a single group pretest-posttest design
to demonstrate that four hippotherapy sessions altered the hormone levels (cortisol and
progesterone) of boys with ASD in a manner that suggests an improvement in social attitudes.
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Also using a single group pretest-posttest design, Ajzenman et al. (2013) demonstrated that 12
weeks of hippotherapy increased postural stability, receptive communication, coping, self-care,
low-demand leisure participation, and social interaction in children with autism. Together, these
studies provide preliminary evidence that hippotherapy has the potential to increase the social
functioning of children with autism. However, these studies are limited in that they use singlesubject or single-group designs and small sample sizes; furthermore, hippotherapy has not been
compared to standard of care. Therefore, the effects of hippotherapy on social functioning of
children with autism still need to be investigated using a rigorous experimental design providing
a comparison to current standard of care.
Our study aims to assess the effectiveness of hippotherapy focused on improving social
functioning abilities for children with ASD in comparison to standard care. The social
responsiveness scale (SRS) has been chosen as the primary outcome measure to evaluate social
functioning abilities. Specifically, the scale consists of a 65-item questionnaire that assesses the
severity of ASD (Constantino, 2002). This scale is comprised of five subscales: social awareness,
social communication, social motivation, autistic mannerisms, and social cognition.
The intended indication for this study is to establish the efficacy of hippotherapy in
comparison to standard care to improve social functioning in children with ASD. This study is
considered a phase III trial. The hippotherapy intervention involved in our study is based upon
the intervention done by Ajzenman et al. (2013). To increase the rigor of empirical evidence in
this field, this study will be a randomized controlled trial with a primary endpoint of establishing
efficacy for hippotherapy for children with ASD and will utilize blinded assessors to evaluate
primary outcomes.
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Synopsis of Proposed Study
Subject Identification: Patients will be included in the study based on the following criteria:
children between the ages of 5-12; clinical diagnosis of autism spectrum disorder (ASD); were of
full-term birth; have the ability to follow one-step directions and be able to ambulate
independently with or without assistive devices. Patients will be excluded if they meet any of the
following criteria: have severe behavioral issues that can result in self harm or harm to others
and/or to animals; previous exposure to any equine therapy; and have a clinical diagnosis of
severe sensory impairment, cerebral palsy, epilepsy, and other neurological conditions.
Study Treatments: “Hippotherapy is the incorporation of equine movement through physical
therapy, occupational therapy, or speech language pathology professionals in treatment” as
defined by the American Hippotherapy Association (AHA, 2010). The American Hippotherapy
Association defines professionals in treatment as “professionals that use evidence-based practice
and clinical reasoning for the purposeful manipulation of equine movement to engage the
sensorimotor and neuromotor systems to create functional change in the patient” (AHA, 2010).
Hippotherapy will be used as the form of treatment in the intervention group. The control group
will receive standard occupational therapy care in order to compare the outcomes of both the
experimental and control groups. Standard occupational therapy for children with ASD consists
of any traditional outpatient, home health, and/or school-based services, where treatments are
individualized based on the child's needs.
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Study Measurements: The Social Responsiveness Scale (SRS) will be utilized to assess social
functioning at pre/post-intervention for both treatment groups. This scale is a 65-item
questionnaire that consists of five subscales as a means of measuring the severity of ASD
symptoms (Bass et al. 2009). The five subscales consist of the following: social awareness,
social cognition, social communication, social motivation, and autistic mannerisms. Total SRS
scores consist of the summation of the five subscale scores. Patients’ total SRS scores will be
calculated and used to assess the difference of social functioning between pre and post
intervention for both hippotherapy and standard care. A reduction of the composite SRS score
demonstrates an improvement in social functioning.
Figure 1. Visit Table
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Study Design Methods: This study is a 1:1 randomized controlled superiority trial with a less
than hypothesis conducted with children ages 5-12 with ASD. Baseline evaluation will consist of
a pre-intervention evaluation that will take place prior to the 12-week intervention by the child’s
schoolteacher. A post-intervention evaluation will occur after the weekly therapy session at the
end of the 12th week. Subjects will undergo either hippotherapy or standard care for 60-minute
weekly sessions for a total of 12-weeks. The primary objective of this study is to establish
effectiveness of hippotherapy for children with ASD. The primary endpoint will be the
difference in social functioning skills between the intervention and control group; prespecified
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secondary endpoints will be increases in social awareness, cognition, communication,
motivation, and a decline in autistic mannerisms.
Analysis plan: A two-sample t-test analysis will be utilized to test the difference between
intervention group means of the composite SRS. Two-sample t-tests will also be utilized to
assess the difference between treatment group means on each of the SRS subscales to include the
following: social awareness, social cognition, social communication, social motivation, and
autistic mannerisms (secondary endpoints). Variable significance will be assessed at an alpha
level of 0.05.
Inference and Sample size: The primary efficacy outcome measure is the composite score on
the SRS. Based on current literature, we specified a minimal clinically relevant detectable
reduction in social functioning deficits of 10 (difference between mean of 0 for control group
and -10 for treatment group) (Bass et al. 2009). As prior research is limited in this area, to
estimate pooled standard deviation for a 10-point reduction in social functioning deficits Cohen’s
d effect size was used (Bass et al. 2009). Bass et al. (2009) reported an effect size of d= 0.66,
Mpre= 85.9 and Mpost= 73.6, these values represent means of composite SRS scores pre and post
12-week hippotherapy intervention for the intervention group. Based on these values a pooled
standard deviation of 18.64 was calculated.
We selected a sample size of 56 patients per group for an overall sample size of 112 to have 80%
power. Therefore we estimated a standard error of 3.52 (= sd*sqrt(2/56)) and a critical value and
95% confidence interval of -6.9 (-13.8, 0). The design will discriminate between the following
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hypotheses: Ho: Θ ≥ 0; Halt: Θ ≤ -13.8. A sample size of 54 per treatment group would be needed
to have 97.7% power to discriminate between hypotheses and a sample size of 37 per group is
needed to have 90% power.
Study Implementation and Conduct
Recruitment: Subjects will be recruited from the Larimer County school system and the
Larimer County ASD Center for Therapeutic Services based on a known diagnosis of ASD
according to the DSM-IV-TR (APA, 2000) autism spectrum diagnosis. Recruitment will be
monitored by study personnel monthly and if recruitment slows, problem solving may include
more rigorous recruiting for children with autism in Colorado school districts outside of Larimer
County.
Screening: All children referred to the study will be screened for enrollment by the principal
investigator based on the inclusion/exclusion criteria previously discussed.
After screening,
parents will be required to consent to pre-testing, 12 weeks of hippotherapy and one post testing
session prior to enrollment.
Retention: Retention is not expected to be a significant concern with this study given that
autism is considered a chronic condition and many children are not eligible to continue receiving
therapeutic services reimbursed by insurance unless a significant change in condition can be
justified. Therefore, parents are often required to pay expensive therapy costs out of pocket to
ensure their children receive ongoing services. Parents in either group (hippotherapy or standard
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of care) may see this study as an opportunity to receive ongoing therapeutic services without a
financial burden and will be focused on completing the study whether their child is randomized
to the hippotherapy group or the standard of care group. Since all children included in this study
are of the age to attend public school, the study will be completed during the months school is in
session, and the children’s primary teacher will be responsible for completing both pre and posttest assessments. Children randomized to both groups will also receive two free riding sessions
once their post-test assessment has been completed and data has been received by study
personnel.
Non-compliance is not a major concern of the investigators in this study due to the reasons
mentioned above. However, drop-in concerns are more likely to occur than drop-out as some
parents in the standard of care group might be inclined to pay out of pocket for hippotherapy if
they perceive this to be a more superior treatment than standard occupational therapy. The
statistical power of the study will be decreased if subjects do not comply with the treatment
protocol (either group). Therefore, parents will be educated during the consenting process on the
importance of compliance to study allocation.
Randomization: Children who complete the initial screening and pre-testing and are found to
be eligible for this study will be randomized in a 1:1 fashion to either a treatment (hippotherapy)
or control group (standard occupational therapy). A blinded statistician will utilize a computer
generated block randomization scheme stratified based on the composite of the Social
Responsiveness Scale by moderate deficits in social functioning (SRS ≥78) or mild deficits in
social functioning (SRS < 78) to promote comparable groups and to allow for direct analysis of
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the effects of treatment type on severity of disability. It’s expected the severity of disability will
be a strong covariate in predicting overall outcome and stratification will reduce the chance for
confounding in this study. Our analysis must account for stratification of this variable. We will
randomize in blocks of 10 to ensure equal numbers of subjects in each group which should also
increase power and limit confounding. The randomization code will be kept in a secure locked
cabinet within the biostatistician’s office and no other study personnel will have access to this
code. Please see attached appendix with randomization table for this trial.
Blinding: This will be a single blind study with concealed allocation. Challenges with blinding
will be a limitation in this study as it is with many rehabilitation trials, but efforts will be made to
keep outcome assessors (teachers) blinded to group allocation. Standard of care occupational
therapy will be completed in the clinic on-site of the equestrian center so travel for both groups
will be similar and teachers will not be exposed to different travel arrangements. Parents and
children will be asked not to discuss any aspect of their therapy with their teachers, but there is
no way to ensure this does not occur.
Missing Data: The principal investigator will be responsible for obtaining completed pre and
post-test assessments from the blinded assessors within 7 days of completion. She will review
each assessment for completion and notify the blinded assessor immediately of any data that has
not been completed. Study personnel will focus on maintaining study quality control to
eliminate the potential for missing data. However, the recruited sample size will be 10% greater
than the calculated sample size (64 subjects) to account for the possibility of 10% attrition. All
statistical analysis will be completed based on an intention to treat analysis to manage missing
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data. Data will be monitored frequently for missing data which will be corrected as soon as
possible. All subjects (both groups) will be offered two free riding sessions after post-test
assessments have been completed to minimize loss of data.
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References
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Department of Occupational Therapy, University of Colorado State, Fort Collins,
Colorado.