Over a year ago I wrote an article about a case report indicating that, for one child, pressure vests were not found to be effective in promoting engagement behavior (see my criticism of using case reports for conditions that are not extremely rare). The same journal just published a slightly larger, and therefore more informative, study examining the effectiveness of weighted vests for reducing stereotyped behaviors (e.g., hand flapping, sniffing, rocking, spinning objects, echolalia, etc) in children with severe autism. These behaviors can have a negative impact on the child’s social relations and academic functioning, and therefore are often the target of interventions. In the study, Dr. Sandra Hodgettes and her colleagues at the University of Alberta, explained the “homeostatic” theory about stereotyped behaviors in autism. This theory purports that individuals with autism engage in stereotyped behaviors in order to compensate for a state of over or under physiological arousal. That is, stereotyped behaviors are believed to help individuals bring their arousal level back to “normal”. So, how are weighted vests supposed to help?
Pressure or weighted vests are supposed to provide enough sensory stimulation to produce the right amount of physiological arousal so that the person does not need to engage in stereotyped behaviors. If this is true, then the use of weighted vests should have an impact on physiological markers of arousal. For example, if weighted vests reduce physiological arousal, then we should see a change in heart rate. We don’t really know if this is true because the authors indicated that no study had examined the effects of weighted vests on heart rate. Thus, the researchers of this study were interested in examining whether the use of weighted vests would decrease stereotyped behaviors, and whether the vests would impact the heart rate of the participants.
The study involved 6 mostly non-verbal children with severe autism between the ages of 4 and 10 (5 boys and 1 girl). The kids participated in a withdrawal design for 4 weeks, during which they alternated each week between one condition (weighted vest) and the other (no vest). For example, one child would use the weighted vest during week 1, then no vest during week 2, then vest during week 3, and finally no vest during week 4. If the vest is effective, you would see an reduction of stereotyped behaviors during the weeks the child used the vest, and an increase of such behaviors during the weeks he/she didn’t use the vest. Likewise, if the vest had an impact on heart rate, the heart rate would change based on whether or not the child was wearing the vest.
Below you can see the % of intervals during which the child engaged in stereotyped behaviors in one of the participants during the different weeks of the study.
As you can see, during all weeks stereotyped behaviors were observed between 70 and 100% of the time intervals examined, and there was no change across the different weeks. This indicates that the vest had no impact on the presence of stereotyped behaviors. Also, there was no difference between the week the vest weighed 5% of the child’s body weight and when the vest weighed 10% of the body weight. Unfortunately, this was the general patterns among the participants. Overall, the use of the weighted vest did not result in a reduction of stereotyped behaviors or in a change in heart rate. This is consistent with most of the previous studies that have used the proper research designs and which have also failed to find evidence for the effectiveness of these vests.
There was one exception, however. In one child, the weighted vest resulted in an 18% decrease in stereotyped behaviors, which led to a PND of “questionable effect”. PND is a statistic that examines the likelihood that the effect observed is due to the treatment as opposed to chance or other factors. So sadly, even for the single child for which the vests appeared to be effective, it was unlikely that the effect observed was due to the treatment.
The authors concluded:
This study’s results do not support the use of weighted vests to decrease motoric stereotyped behaviors, nor does it support the theoretical basis for this modality.
Although we need studies with significantly more participants so we can firmly establish whether these vests are effective, the best studies to date have failed to show that this intervention is effective in reducing stereotyped behaviors in most children.
Hodgetts, S., Magill-Evans, J., & Misiaszek, J. (2010). Weighted Vests, Stereotyped Behaviors and Arousal in Children with Autism Journal of Autism and Developmental Disorders DOI: 10.1007/s10803-010-1104-x
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