The Use of Weighted Vests with Children with Autism Spectrum Disorders and Other Disabilities

Abstract

Therapists who use sensory integration therapy may recommend that children wear weighted vests as an intervention strategy that they claim may assist in remediating problems such as inattentiveness, hyperactivity, stereotypic behaviors and clumsiness. Seven studies examining weighted vests are reviewed. While there is only a limited body of research and a number of methodological weaknesses, on balance, indications are that weighted vests are ineffective. There may be an arguable case for continued research on this intervention but weighted vests cannot be recommended for clinical application at this point. Suggestions are offered for future research with regard to addressing methodological problems.

Full text

ORIGINAL PAPER
The Use of Weighted Vests with Children with Autism Spectrum
Disorders and Other Disabilities
Jennifer Stephenson Æ Mark Carter
 Springer Science+Business Media, LLC 2008
Abstract Therapists who use sensory integration therapy
may recommend that children wear weighted vests as an
intervention strategy that they claim may assist in reme-
diating problems such as inattentiveness, hyperactivity,
stereotypic behaviors and clumsiness. Seven studies
examining weighted vests are reviewed. While there is only
a limited body of research and a number of methodological
weaknesses, on balance, indications are that weighted vests
are ineffective. There may be an arguable case for con-
tinued research on this intervention but weighted vests
cannot be recommended for clinical application at this
point. Suggestions are offered for future research with
regard to addressing methodological problems.
Keywords Sensory integration  Weighted vests 
Autism  ADHD
Sensory Integration (SI) therapy is a popular and widely
used therapy for children with autism (Green et al. 2006;
Roberts 2004). Green et al. reported that 38.2% of children
with autism were currently receiving SI and 33.2% had
received it in the past. SI has been recommended for people
with autism, cerebral palsy, learning disabilities, intellec-
tual disability, ADHD, communication difficulties and
other problems (Densem et al. 1989; Mauer 1999; Olson
and Moulton 2004a).
Sensory integrative therapy is based on the proposition
that functional performance deficits in individuals result
from a failure to appropriately process sensory information.
Therapy is directed at altering underlying neurological
processing (Ottenbacher 1982; Schaaf and Miller 2005;
Vargas and Camilli 1999) rather than developing skills
directly. Traditionally, intervention has involved treatment
sessions delivered by an occupational therapist in which
controlled sensory stimulation is provided. Such interven-
tion typically involves such activities as brushing and
rubbing of the body, deep pressure and compression of
joints, as well as use of hammocks and scooter boards to
provide stimulation (see Ayres 1972; Hoehn and Baumei-
ster 1994; Smith et al. 2005). A more recent innovation has
been the use of ‘‘sensory diets’’ that involve activities and
environmental adjustments, purported to complement the
individual’s individual sensory needs (Smith et al. 2005).
A recent treatment generally included under the
umbrella of SI is the wearing of weighted vests. A
weighted vest is ‘‘…a vest that typically has 10% of a
person’s body weight evenly distributed around the vest.’’
(Olson and Moulton 2004b, p. 53). Therapists working
within a sensory integrative therapy framework believe that
a range of problems, such as inattentiveness and stereotypic
behaviors, may be due to over- or under-sensitivity to
sensory input. A weighted vest can provide sensory input
that is believed to alleviate some of these difficulties (Ol-
son and Moulton 2004b). Specifically, it is argued that
wearing weighted vests provides the individual with deep
pressure stimulation that has a calming (VandenBerg 2001;
Deris et al. 2006) and organizing (Deris et al. 2006) effect
on the central nervous system. It has been suggested that
such pressure may affect several deep brain structures,
including the reticular activating and limbic systems, thus
decreasing arousal (VandenBerg 2001). Changes in
underlying neurological processing of sensory information
associated with wearing of weighted vests are proposed to
result in improvements in a range of behaviors including
J. Stephenson (&)  M. Carter
Macquarie University Special Education Centre,
Macquarie University, Sydney, NSW 2109, Australia
e-mail: jennifer.stephenson@speced.sed.mq.edu.au
123
J Autism Dev Disord
DOI 10.1007/s10803-008-0605-3

stereotypy (Deris et al. 2006; Kane et al. 2004–2005),
attention (VandenBerg 2001; Kane et al. 2004–2005) and
hyperactivity (VandenBerg 2001).
There is evidence to suggest that weighted vests are used
widely in clinical practice and practitioners believe they are
effective. Green et al. (2006) reported that 12.8% of chil-
dren with autism were currently using weighted vests or
blankets and 25.7% had used them in the past. Olson and
Moulton (2004a) surveyed a convenience sample of 51
occupational therapists, all of whom used weighted vests in
their practice, to ascertain their experiences using weighted
vests with children with developmental disorders. The
therapists reported the use of weighted vests with children
with Autism Spectrum Disorder, ADHD, sensory integra-
tive disorder, cerebral palsy, developmental delay, Down
syndrome and traumatic brain injury. Therapists reported
increases in desirable behaviors and decreases in problem
behaviors as result of vest use in children with ASD, ADHD
and sensory integrative disorder, although many also noted
no change for a range of behaviors. Although the vests were
also used to improve posture and balance (especially in
children with cerebral palsy), the main use was to ‘‘Calm a
child and improve attention to academic classroom work’’
(p. 59). Most of the positive changes were noted while the
children wore the vests and some were believed to be
maintained after the vest was removed. Weighted vests
were often used with other strategies and some therapists
believed the vests alone would be insufficient to cause
change. This survey showed a range of practices in the use
of vests, with no consistency in the weights used (between
0.25 and 2 kg, and up to 10% of the child’s weight) or the
length of time worn (10 min to most of the school day). The
use of the vests did not vary across disability groups.
Olson and Moulton (2004b) also carried out a mail survey
of occupational therapists exploring similar questions and
obtained a response rate of 68% from a random sample 514
therapists working with children. Of this sample, 56.6% used
weighted vests and reported use with people with autism/
PDD, ADHD, developmental delay, cerebral palsy and
Down syndrome, mostly pre-school and young elementary
school students. Again there was considerable variation in
the way the vests were used with weight varying from 2 lbs to
over 5 lbs, length of use from under 1 h to over 4 h and from
once to four times daily. Most therapists in this survey
reported that they thought use of the vests could improve on-
task and in-seat behavior and attention to tasks and decrease
some self-stimulatory behaviors and high activity levels.
Morrison (2007) recently provided an analysis of arti-
cles examining the use of weighted vests for children on
the autism spectrum. Only three empirical studies were
identified and critical analysis of the methodology was
restricted. Nevertheless, Morrison concluded that research
was limited and more compelling evidence was needed.
As there is little research support for Sensory Inte-
gration therapy as a general intervention strategy, it is of
interest to explore the research base for this popular and
readily defined practice, with a particular focus on the
strength of the research methodology employed. Is there
good research evidence to support the use of weighted
vests to increase attentive, on-task behavior and reduce
distractibility and self-stimulatory behaviors in children
with disabilities?
Method
A search was carried out using Google Scholar, PsychInfo,
ERIC and CINAHL using the search terms ‘‘weighted
vest’’ and ‘‘weighted vests’’. The reference lists of articles
located in this way were checked for additional studies.
Articles located were included in this review if they
explored the use of weighted vests to improve the behavior
of children with disabilities and presented empirical data.
Initially, the intent was to limit the analysis to peer refereed
sources but considering the dearth of studies, it was deci-
ded to expand the review to non-refereed sources as well.
Results
Five peer-reviewed papers were located. An additional
study (not peer-reviewed) was located in ERIC (Deris et al.
2006) and a recent poster presentation (Barton et al. 2007)
was drawn to our attention by a colleague. See Table 1 for
details of studies.
Participants
Overall, the studies investigated the behavior of 20 stu-
dents, 9 with autism, 4 with pervasive developmental
disorder (PDD), 1 with PDD (not otherwise specified), 1
identified with ASD, 1 identified with developmental delay
and autistic-like behaviors, 2 with ADHD and 2 with
ADHD and speech and language impairments. The stu-
dents ranged in age from 2 years 7 months to 11 years, but
only four children were older than 7. Participant descrip-
tion was extremely limited in the vast majority of cases, in
most instances amounting to little more than an age,
diagnostic label and description of behaviors of concern.
Only three studies (Kane et al. 2004–2005; Myles et al.
2004; VandenBerg 2001) provided any documentation of
how the diagnosis was made. Only two studies provided
standardized information on cognitive or developmental
performance, although only a disability level was provided
by Carter (2005) and data were only provided on 2 of 3
participants by Myles et al. (2004).
J Autism Dev Disord
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Table 1 Summaries of studies reviewed
Study Participants and behavior Design Vest characteristics Reported Outcome
Deris et al.
(2006) (ERIC
document)
4 year old boy with ASD. Attention to
task and self-stimulation
Alternating treatment design comparing no
vest, to pressure vest and weighted vest
Weight—3 lbs (approx 10% of body
weight). Worn for 30 min intervals
every 2 h throughout day. Assessed
after having worn vest for at least
15 min
No clinically significant effect on self-
stimulation or attention to task
Barton et al.
(2007)
(Poster)
4 year old boy with autism (Tommy) Alternating treatment design comparing
weighted vest, vest without weights and no
vest (observers were blinded when vest was
weighted. Engagement, non-engagement,
stereotypic behavior and problem behavior
were measured during morning table-time
activities (painting, gluing, coloring and
cutting)
No details of weight. Tommy wore
irregularly and Bert wore for part of
each school day
No difference in engagement across
conditions
Tommy’s problem behaviors increased
while wearing the vest, but
stereotypic behaviors decreased
4 year old boy with developmental-delay
and autism-like behaviors (Bert)
Carter (2005)
(Refereed
article)
4 year old boy with autism Alternating treatment functional analysis of
SIB (attention, demand, alone and play
conditions) when infection was present/
absent and when vest was present/absent
Weight—3 lb (7.5% pf body weight) SIB was more likely to be present when
student had a sinus infection, high
rates across all conditions showed it
was maintained by automatic
reinforcement
Worn during 5 min assessment
sessions
Presence or absence of vest had no
effect
Self-injurious behavior (hitting head or
back of hand)
Fertel-Daly et al.
(2001)
(Refereed
article)
2 years 7 month girl with PDD Observation of behavior during a 5-min fine
motor activity
Weight of 1 lb in all vests. Worn for 2
hr and observations made after the
vest was worn for 1.5 h
Participant 1 showed most attention,
fewest distractions in the vest
condition, and least self-stimulatory
behavior in baseline
2 years 10 month boy with PDD Participant 2 showed most attention and
least distraction in the vest condition
and most self-stimulatory behavior in
the withdrawal condition
3 years 1 month boy with PDD Participant 3 showed most attention and
least distractions and stereotypy in
the vest condition
2 years 9 month girl with PDD Participant 4 showed most attention in
the vest condition, least distraction in
the vest condition and least
stereotypy in the withdrawal
condition
2 years 10 month boy with autism Participant 5 showed most attention in
the vest condition, least distraction
and least stereotypy in the vest
condition
All had some self-stimulatory behavior
and problems attending to task
These judgments were made on means
J Autism Dev Disord
123

Table 1 continued
Study Participants and behavior Design Vest characteristics Reported Outcome
Kane et al.
(2004–2005)
(Refereed
article)
8 year old boy (Jerry) with autism ABC design involving baseline (no vest);
weighted vest and vest without weights
(treatments were counter-balanced
across the 4 participants)
Weight—5% of individual’s body weight Jerry’s attention to task increased
slightly with the no-weight vest, and
stereotypy also decreased during this
condition. Stereotypy was highest
during the weighted-vest condition
10 year old girl (Elsie) with autism Placed on child 1 min before the 10 min
observation session
Elsie’s stereotypy occurred during
100% of intervals in all conditions.
Attention to task was best in baseline
11 year old girl (Eileen) with autism Norman had high levels of stereotypy in
all conditions, and attention to task
was highest in baseline
8 year old boy (Norman) PDD-NOS Eileen engaged in stereotypy for 2.5%
of intervals in baseline and not at all
in either vest condition. Attention to
task was highest in baseline
All with stereotypic behaviors
Myles et al.
(2004)
(Refereed
article)
Student 1, boy, 5 years 7 months, autism,
developmental age 20 months, non-
verbal
ABAB designs. Comparing on task
behavior (first and second students) and
duration of self-stimulation (third
student) during school activities.
Observations were made in 5 min
individual sessions and group sessions
of unspecified length for student 1 and
group activities of 15 min for students 2
and 3
Weight—10% of child’s boy weight for
student 1 and 5% for students 2 and 3
Student 1—no clinically significant
changes
Student 2, boy, 3 years 6 months, autism,
nonverbal
Vests worn for duration of activities for
student 1 (5 min) and student 2
(15 min). For student 3 vest was worn
for 30 min BEFORE activity and
removed for the activity itself (15 min)
Student 2—mean increase of on task
time from 9 to 34% (based on graphic
data)
Student 3, boy, 4 years 11 months,
autism, developmental age 22 months,
some verbal skills
Student 3—mean time spent in self-
stimulation decreased from 19 to 6%
VandenBerg
(2001)
(Refereed
article)
Student 1, girl, 6 years 10 months, speech
and language impairment, ADHD
AB design. Measured ‘‘on-task’’ behavior
during a wide range of fine-motor
activities. A phase, without vest and B
phase with vest. Also wore vests at
other times
Weight—5% of child’s body weight Student 1—25% mean increase in time
on task while wearing vest
Student 2, girl, 6 years and 6 months
speech and language impairment,
ADHD
15 min observations Vests put on 5 min before the observation
interval and removed after 20–30 min
Student 2, 3, 4—Mean increase of 17–
18% time on task
Student 3, boy, 6 years and 9 months
ADHD
Student 4, boy, 5 years and 9 months,
ADHD
Excessive movement, overreaction to
extraneous stimuli, inability to
complete tasks, difficulties with fine-
motor tasks
J Autism Dev Disord
123

Research Design
All studies used small n research designs. Three studies
used relatively weak AB (VandenBerg 2001), ABA (Fer-
tel-Daly et al. 2001) or ABC (Kane et al. 2004–2005)
designs. Kane et al. (2004–2005) also counterbalanced the
treatment order across participants in the intervention
phase. Three studies (Deris et al. 2006; Carter 2005; Barton
et al. 2007) used variations on the stronger alternating
treatment design and Myles et al. (2004) used a series of
ABAB designs.
Dependent Variables and Observations
Results were reported for self-stimulatory or stereotypic
behavior (12 students), attention to task or task engagement
(17 students), distracted or off-task (5 students) and prob-
lem behavior (1 student). With the exception of Carter
(2005) who used short functional analysis across 72 ses-
sions, all studies were of relatively short length, involving a
total of 11–25 sessions. While the data for student 2 in the
Myles et al. (2004) study extended over a potential total of
40 sessions, a considerable amount of the data was missing.
Further, the observation periods monitored were very short,
between 5 and 15 min in the studies that provided this
information.
Independent Variables
In the studies that provided both vest weight and partici-
pant body mass, vest weight ranged from 5 to 10% of body
mass. In the study by Fertel-Daly et al. (2001), a fixed
weight was used. There was considerable variation in
procedural aspects of the studies. Vests were worn for as
little as 5 min (Carter 2005; Myles et al. 2004, student 1)
and as much as 2 h continuously. In some studies (Carter
2005; Kane et al. 2004–2005; Myles et al. 2004, students 1
and 2) observation started immediately or soon after vests
were placed on participants and in others (Deris et al. 2006;
Fertel-Daly et al. 2001; VandenBerg 2001) after a delay of
5 min to 1.5 h. Myles et al. (2004) reported that their third
student wore the vest for 30 min prior to the activity and
then removed it for the activity and data collection.
Reliability
The observation and recording arrangements in several
studies were less than ideal. While VandenBerg (2001)
reported that observers did practice observations on chil-
dren not involved in the study beforehand to check that
they could reach appropriate levels of reliability, they
failed to evaluate interobserver reliability for the actual
observations in the study. In this study one of the observers
was the occupational therapist who was treating the chil-
dren, and the other was an occupational therapy student.
One observer collected baseline data and the other observer
collected intervention data, with the observer who col-
lected the intervention data unaware of the results from the
baseline phase. In the Fertel-Daly et al. (2001) study, the
first author collected all the data. While another observer
also collected interobserver reliability data on 20% of
sessions, problematically, this was limited to the baseline
phase. That is, there was no interobserver reliability col-
lected for the intervention conditions. Myles et al. (2004)
failed to report any reliability data for student 2. For stu-
dent 3, they presented duration data but reported event
reliability, making the reliability data irrelevant. Kane et al.
(2004–2005) collected no interobserver reliability data at
all.
Given the nature of the intervention, one obvious way to
control for observer expectancy effects would be to use
vests both with and without weights and observers blind to
these conditions. Only in the study of Barton et al. (2007)
were the observers blind to the presence or absence of
weight in the vest. While Kane et al. (2004–2005) did
include a phase where the vest was worn without weights,
the observer was aware of the presence or absence of
weight.
Results
The presence of a weighted vest was reported to reduce the
stereotypic behavior of 5 students and attention or
engagement in a task was reported as highest in the
weighted vest condition for 10 students. The vest had no
effect on problem behavior for the 1 student where this was
measured. The authors in four studies (Barton et al. 2007;
Carter 2005; Deris et al. 2006; Kane et al. 2004–2005)
concluded that weighted vests were an ineffective inter-
vention. Authors in one study found mixed results (Myles
et al. 2004) and authors in the remaining two (Fertel-Daly
et al. 2001; VandenBerg 2001) claimed positive effects.
Discussion
It is clear that consistent positive effects of the wearing of
weighted vests have not been demonstrated, a finding
consistent with research on sensory integration therapy in
general (see Arendt et al. 1988; Baranek 2002; Dawson and
Watling 2000; Hoehn and Baumeister 1994; Hyatt et al. in
press; National Research Council 2001; Leong and Carter
2008; New York State Department of Health 1999; Perry
and Condillac 2003; Roberts 2004; Shaw 2002; Vargas and
Camilli 1999). In four of the studies examined, the vests
had no clinically significant effect on behavior. In two
J Autism Dev Disord
123

studies (Fertel-Daly et al. 2001; VandenBerg 2001) posi-
tive effects were claimed and Myles et al. (2004) reported
mixed results, but there were some important interpretive
problems and further discussion is warranted.
As previously noted, VandenBerg (2001) and Fertel-
Daly et al. (2001) used relatively weak research designs.
Presentation of data was problematic in the Fertel-Daly
et al. (2001) study. While students were observed for a total
of 300 s, time scales in the vertical axis of graphs were
variable and the presented range was as low as 30 s. This is
similar to the ‘‘Gee Whiz!’’ strategy (see Runyon and
Haber 1967) where the range of the ordinate is restricted to
exaggerate effects. For example, when the increases in the
duration of focused attention from baseline to intervention
are calculated as a percentage of the total observation time,
the mean increase was only 8.2% (range 3.8–12.2%) with
two values below 5%. In relation to the duration of self-
stimulatory behaviors, 3 participants showed an increase or
decrease of 3% or less of the total observation time. The
remaining two participants demonstrated decreases of 14
and 42% from baseline to intervention but in both cases,
further decreases were evident when the intervention was
withdrawn. Further, incomplete return to baseline was
evident in quite a number of the graphs presented. Fertel-
Daly et al. (2001) reported a mean increase in the duration
of focused attention of 11.4 s between baseline and inter-
vention and a mean difference of 23.4 s between baseline
and withdrawal. The differences in the means for self-
stimulatory behavior were 5.6 and 16.2 s. These represent
very small changes in behavior overall (at the most a dif-
ference of 7.8%), and given the range of the individual
observation points, it could not be claimed that these were
clinically important differences.
While strategies for summarizing results of small n
research designs remain controversial, the most widely
accepted metric is percentage of non-overlapping data
(PND) (see Reynhout and Carter 2006). PND is calculated
by determining the percentage of intervention data points
that exceed the highest (or lowest if behavior decrease is
anticipated) data point in the immediately preceding
baseline (Scruggs et al. 1987). A PND between 91 and 100
indicates a highly effective intervention, between 71 and
90 a moderately effective intervention, between 51 and 70
mildly effective intervention, and between 0 and 50, a non-
effective intervention (Mastropieri et al. 1996). Calculated
on the initial baseline—intervention sequence, the mean
PND for focused attention was 48, the mean PND for
number of distractions was 100, which was incongruous
with the focused attention value. The PND for self-stimu-
lation was 56. The extent of data overlap was also
problematic in the VandenBerg (2001) study. The PND
was only 50 for 2 of the 4 participants and the mean study
PND was 67.
The approach to data analysis in both studies warrants
some comment. VandenBerg (2001) used two approaches
to analysis. First, the two standard deviation method was
applied where an intervention is deemed effective if
intervention data points exceed baseline by two standard
deviations. This approach is not widely employed in small
n research and is inherently problematic. In contrast to
standard deviations calculated for group data, repeated
measurement of the behavior of a single individual would
be expected to be correlated with consequent constraint of
standard deviation values and inflated effect sizes (Leong
and Carter 2008). For example, in a sample of 100 AB
panels from small n studies reported by Matyas and
Greenwood (1990), the median effect size was 9.2 while
the 25th percentile was 4.7 and the 75th was 17.1 (in
comparison, in group research an effect size of 1 is con-
sidered large). Thus, intervention effects that approach two
standard deviations can be reasonably considered small by
the standards of small n research. The second approach
involved use of a binomial test to compare the proportion
of data points in each phase above a trend line derived from
baseline data. Again, this procedure is not commonly
employed in small n research and, unfortunately, there is
considerable doubt about its ability to control Type I (false
positive) error (Crosbie 1987). Fertel-Daly et al. (2001)
relied on a more conventional visual analysis of data.
While they did note that trend was considered, data were
reported almost exclusively in terms of mean level across
phase. Further, the high variability that was present in
much of the data did not appear to be sufficiently
considered.
Although Fertel-Daly et al. (2001
) and VandenBerg
(2001) have drawn on applied behavior analysis for their
experimental designs, they have not acknowledged the
important principles underlying applied behavior analysis
and the interpretation of the graphs in small n designs.
Researchers are primarily looking for interventions that
bring about a change that is meaningful in terms of applied
or clinical significance, and can then be recommended to
clinicians because they have resulted in important and
robust changes in behavior (Baer et al. 1968; Kazdin 1982).
The effects of an intervention should be clearly visible in
the graphed results, and thus analysis by visual inspection
only can act as a filter to screen out weak interventions
(Kazdin 1982). Certainly effects that are not apparent on
visual inspection may be uncovered by statistical treat-
ments, but these effects are not those that suggest powerful
and effective interventions. It may be that the VandenBerg
(2001) and Fertel-Daly et al. (2001) studies have uncovered
weak effects through the additional statistical analysis, and
this should not be overlooked. The results, however, are not
indicative of strong clinical effects that can be reliably
transferred to practice.
J Autism Dev Disord
123

Other weaknesses in the Fertel-Daly et al. (2001) and
the VandenBerg (2001) studies are that the conditions were
less well controlled than some other studies. In both, there
was no control over the activities the students were
involved in, beyond that they were table-top, fine motor
tasks. Also in both these studies it appears that the teacher
interacted with the students while they were engaged in the
activities, and this was not controlled. In the distraction
measurement observations in the Fertel-Daly et al. study,
there was no control over external events that could have
been potentially distracting for the students. There was
strong control over the conditions in Kane et al. (2004–
2005) as all students were engaged in an activity inde-
pendently and the same activity was used in each
observation for each participant. The Carter (2005) study
employed standard, tightly controlled conditions adminis-
tered by a researcher as is characteristic for the procedures
for functional analysis (Iwata et al. 1994).
Myles et al. (2004) used a stronger research design, but
their study warrants closer examination. For the first stu-
dent, they reported only a mean difference of about three-
seconds between intervention and baseline phases in the
one-to-one setting, but this cannot be confirmed because
the graphic data they refer to is not present. In the case of
the group setting for this student, the mean data presented
for combined baseline and intervention phases appears to
be incorrectly calculated (it is about double the mean for
each phase). The relevant graph (apparently the second
graph in the article, rather than the first as indicated by the
authors) was scanned and data extracted using the Digiti-
zeIt (Bormann 2003) computer program. When data were
pooled across baseline and then intervention phases, the
mean difference was less than 1%, although this point is
somewhat moot as the authors conclude there was no
clinically significant effect. The data for student 2 appeared
to be contained in the third figure in the article (not Fig. 2
as indicated by the authors). While there appears to be
evidence of a clinically significant effect, the mean figures
presented by the authors do not correspond to the data on
the graphs. Again, the DigitizeIt program (Bormann 2003)
was used to extract data from the relevant graph. Mean on-
task behavior was 79 s for phase A1 (compared with a
reported mean of 72 s), 316 s for B1 (compared with
237 s), 85 s for A2 (compared with 86 s) and 301 s for B1
(compared with 321 s). While it is conceivable that the
differences in phases A1 and B2 could be due to error in
the scanning process, particularly given the large scale
range of the y axis, there was a clear error in either the
graphed data or summary for B1, which undermines con-
fidence in these data. It should also be noted that much of
the data for the second baseline was missing. As previously
noted, no interobserver reliability data were presented for
this participant.
The intervention with the final student was interesting.
The aims of the intervention were to increase on-task
behavior and reduce self-stimulatory behaviors that were
reported as disruptive during circle time, when children sat
on the floor. The following description of the self-stimu-
latory behaviors was provided:
Carlton engaged in the following deep pressure touch
seeking behaviors while seated on the floor during
circle time (a) lying down completely on back or
stomach, (b) learning (sic) to side onto an extended
arm, (c) learning (sic) back or forward onto both of
his hands, (d) resting his chin in his hand with arm
flexed and elbow resting on floor or on his leg, and (e)
sitting on one or both hands. (p. 55)
With the exception of the first listed behavior, which
might be considered disruptive, these appear to describe
typical sitting positions young children would be expected
to assume when on the floor. It is not immediately apparent
why such behaviors would be considered disruptive and
they would not seem to be incompatible with on-task
behavior in a group setting, which was not actually
reported in the study. While the justification for classifying
a range of typical sitting behaviors as self-stimulatory is
not clear, it could perhaps be argued that any behavior may
be regarded as stereotypic if performed excessively. The
targeted behaviors combined, however, peaked at a mean
duration of only around 3 min (in phase B2) in a 15 min
observation period (see the first figure in the article, not
Fig. 3 as indicated) and this would hardly seem excessive.
Thus, while an intervention effect was apparent from the
graphed data, given the information provided, it remains
highly questionable whether the dependent variable was
socially valid and there was no evidence that the inter-
vention resulted in the targeted change in on-task behavior.
The presentation of reliability data that was not relevant to
the dependant variable again weakens confidence in the
study.
In summary, a number of studies reported positive
findings. Fertel-Daly et al. (2001) and VandenBerg (2001)
both used weak research designs and while positive effects
were claimed, on closer examination, they were inconsis-
tent across behaviors and/or participants. Further, there
were major interpretative problems with both studies.
Myles et al. (2004) used a stronger research design but
confidence was undermined by clear errors in the reporting
of the study and questions about the validity of the
dependent variable in one instance. Unfortunately, these
serious problems mean the results of the research should be
treated with great caution.
There were a number of general weaknesses in the
studies examined in this review. Basic interobserver reli-
ability was missing or inadequate in more than half the
J Autism Dev Disord
123

studies examined. Further, ideally, observers should be
blind to the intervention phase to reduce the possibility of
expectancy effects. The nature of this intervention creates
the obvious opportunity to use a condition in which the
observer is blind to the presence of weight in the vest.
Despite the very simple nature of this manipulation and
somewhat surprisingly, only a single study employed such
blinding.
Studies were limited by short observation periods of 5–
15 min taken over short times spans. Fertel-Daly et al.
(2001) acknowledged the possibility that some of the pat-
terns in their data may relate to a novelty effect and that the
impact of wearing a vest may wear off over time. Thus, if
this intervention is to be researched further, it would seem
critical that the effects are monitored over longer obser-
vation periods and extended time spans.
The weak positive effects reported in the Fertel-Daly
et al. (2001) and VandenBerg (2001) studies, as well as the
results of Myles et al. (2004), may well be accounted for by
problems in design, measurement and interpretation. Nev-
ertheless, it remains possible that the intervention may be
suited to a small number of individuals with specific
characteristics. Unfortunately, the scant participant
descriptions provided in the body of research as a whole
make exploring this proposition very difficult.
Myles et al. (2004) note that ‘‘sadly, it is our experience
that at least in some settings students with ASD are rec-
ommended for weighted vest treatment independent of
their particular characteristics and appropriateness for this
method’’ (p. 59). Noting that they only claim success for 2
of 3 participants, it appears that Myles et al. also had dif-
ficulty making the determination of who was an
appropriate candidate. This should not be surprising given
the selection criteria for participants in the studies exam-
ined. The weighted vest intervention was applied to
students with problematic behaviors who were described as
having sensory modulation disorder (VandenBerg 2001)
and sensory integration needs (Kane et al. 2004–2005),
although, at best, minimal detail was provided on how
these diagnoses were made. For two participants, Myles
et al. (2004) reported that the intervention was selected on
the basis of functional analysis or assessment, but no
details were provided of the procedures used. In other
cases, the prescription of weighted vests was apparently
based on presenting behaviors such as stereotypy or dis-
tractibility (e.g., Deris et al. 2006; Fertel-Daly et al. 2001).
Thus, the obvious question arises as to how individuals
who might benefit from the intervention should be selec-
ted? Should it be used for all individuals with presenting
behaviors such as stereotypy or distractibility, or is a
diagnosis of sensory integrative disorder also necessary? If
so, what objective and replicable procedures should be
used to make this diagnosis? The present corpus of studies
provides very little coherent guidance on this matter,
consistent with other recent research on sensory integrative
therapy (see Leong and Carter 2008).
The effect of prolonged wearing of a weighted vest
needs to be considered. It is recommended that children
carry no more than 10–15% of their body weight in a
backpack (Weinstein 2002) and recent research evidence
indicates that 10% is a safer limit (Moore et al. 2007).
While the weight in a vest is more evenly distributed than
in a backpack, the maximum weight used in the studies was
at the upper end of the safe range. While a vest was worn
for a maximum of 2 h at a time in studies in the current
review (i.e., Fertel-Daly et al. 2001), it has been reported
that they can be worn for up to 4 h at a time (Olson and
Moulton 2004b) and for most of the school day (Olson and
Moulton 2004a). Clearly, these are much longer periods
than a backpack would typically be carried by a child. One
issue that does need consideration is the effect per se of
carrying this amount of weight, suspended above the centre
of gravity, particularly for an extended period of time. If
vests do have effects, and the evidence on this point
remains unconvincing at this stage, it is possible that these
may be artifacts of fatigue and unrelated to purported
sensory integrative mechanisms.
Consistent with research on traditional sensory integra-
tion therapy (see Arendt et al. 1988; Baranek 2002; Hoehn
and Baumeister 1994; Leong and Carter 2008
; Schaffer
1984) the quality of much of the research examining
weighted vests was quite poor. VandenBerg (2001) justi-
fied the use of a weak AB design on the basis that
withdrawal of an apparently effective intervention would
have been unethical, a surprising argument given the
intervention was only in place for about 30 min daily. This
line of reasoning has been presented previously in relation
to sensory integrative therapy (see Leong and Carter 2008).
In general terms it can be strongly argued that the potential
harm of relatively short-term denial of treatment in order to
evaluate efficacy is much less than the long-term harm in
investing time and resources in a potentially ineffective
intervention. In terms of this specific intervention, the
evidence reviewed in this paper unequivocally establishes
that researchers should have no ethical concerns about
withholding treatment for the purposes of scientifically
evaluating the intervention.
Weighted vests are reportedly a widely employed
intervention. While it should be acknowledged there is only
a limited body of research, on balance, indications are that
weighted vests are ineffective. There may be an arguable
case for continued research on this intervention but future
investigators need to ensure that: criteria for participant
selection are replicable and justifiable; participants are
adequately described; interobserver reliability is satisfac-
torily established; observers are blinded to the presence of
J Autism Dev Disord
123

weight in the vests; results are appropriately interpreted
with consideration of the functional magnitude of changes;
more stringent research designs (such as alternating treat-
ment or multiple baseline designs) are employed. Until
such time as well-conducted studies can provide replicated
evidence to the contrary, weighted vests cannot be rec-
ommended for clinical application.
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