Saturday, March 01, 2014
More research on effects of weighted vests on attending behaviors.
I was very happy to see another article on weighted vests in the current issue of AJOT (Lin, Lee, Chang, and Hong, 2014). The last opportunity we had to look at this issue was the excellent pilot study completed by Collins and Dworkin and published in the November/December 2011 AJOT. In that study (reviewed here) the authors found that the weighted vests were not effective in increasing time on task, but cautioned that the results should be generalized cautiously owing to the small sample size and participant selection process.
The current study, completed by colleagues in Taiwan, employed a much more rigorous randomized and two period crossover design with a much larger sample of children. 110 children participated in the study that measured their performance on the Conners' Continuous Performance Test and recorded behaviors during weighted and non-weighted vest wearing conditions.
The researchers made good attempts to control for bias by blinding the video coders to the weighted vs. non-weighted condition. Additionally, the Conners itself is an objective measurement of attending skills. They also used the two group design that presented the weighted vs. non-weighted conditions in reverse order to control for practice effect. Finally, age and gender were non-factors despite the random assignment.
The children wearing the weighted vests made fewer omission errors and had improved response time. The omission error rate is something that has direct functional impact and can probably be fairly extracted to a point of relevance in a clinical context. It is difficult to know the clinical significance of the response time improvements because the differences are measured in milliseconds. That is an issue I am not sure how to resolve, and it would be interesting to hear other people's opinions on this. There was no difference between the groups on commission errors (a measure of impulsivity).
The researchers make appropriate note of some potential limitations, but their design still represents a significant step forward from what has previously been done. They make note that there was not a 'no vest' condition but that would create blinding problems for video coders. I think that the steps they took to use a non-weighted vest as substitute were reasonable. They note that there was no control for subtype of ADHD, and I agree that this could be potentially important. We know that ADHD is not a heterogeneous condition, and it is possible that different factors can contribute to the diagnosis. For these reasons I think it would be very helpful to separate out Inattentive type from Hyperactive-Impulsive type - it would yield much more valuable data in case the neurophysiologic underpinnings of these types are different.
One very important consideration is whether or not the controlled environment and singular focus of the testing protocol was a mitigating factor that helped some children. So, the question I had after reading this was: given that these findings are notably different from other studies, is the weighted vest condition only helpful when all other environmental and contextual distractions have been limited? Using the Conners in a controlled context is nothing like the real-world context of the classroom, and this is an important confounding variable to consider. For this reason I still liked the Collins and Dworkin methodology of videotaped recording and behavioral observations in the classroom. Did the previous researchers not find any functional impact of the vests because the typical classroom distractions override any potential benefit that might have been seen if the testing conditions were more artificial like the current study? Again, this is where the sub-typing analysis would be very helpful, because there is an open possibility that Impulsivity types are simply helped less by weighted vests, particularly in complex classroom environments where distractions are constant.
I don't know that I will make a sudden jump to wanting to use weighted vests, but in my opinion this is an excellent research study and it really gives us a lot of information to think about. I commend these authors for this excellent progression of research in this area and for the very conservative and reasonable implications that they ascribe to their findings. I hope that they continue with this research and strongly suggest that all OTs watch for excellent work like this that helps us better frame our clinical decisions.
Collins, A. & Dworkin, R.J. (2011). Pilot Study of the Effectiveness of Weighted Vests. American Journal of Occupational Therapy, 65(6), 688-694.
Lin, H., Lee, P., Chang, W., and Hong, F. (2014). Effects of weighted vests on attention, impulse control, and on-task behavior in children with attention deficit hyperactivity disorder. American Journal of Occupational Therapy, 68, 149-158.