There is a study that was announced this week by the Sensory Processing Disorder Foundation about classification of sensory processing differences in children (James, et. al, 2011). The study describes a process of using cluster analysis to differentiate subtypes of sensory processing disorder. Results of this study indicate support for the empirical nosology proposed by Miller, et.al. (2007).
Schaaf and Davies (2010) explicitly talked about the need to careful consideration while we are refining and redefining sensory integration or sensory processing concepts. In their article they commended Lucy Miller's group for advancing the theory but at the same time called for empirical evidence to support these concepts. The James, et. al. article seems to be a response to that call.
Of significant concern in this new cluster analysis is that "a high percentage of our sample displayed behaviors characteristic of ADHD and similarly a high percentage of children who met criteria for ADHD were reported to have SMD." ADHD researchers has been grappling with the validity of subtypes for quite a while, so it is a little concerning to see any conclusions being made from this sample of children who have SMD who have such a high co-morbidity of ADHD symptoms.
This is a concern because Rowland, et. al. (2007) and Valo & Tannock (2010) found that data collection methods and who was acting as informant had a significant impact on ADHD classification. This kind of information does not inspire confidence in classification, particularly when the James study on SPD relied heavily on parent report instruments.
Additionally, there has been debate about stability of ADHD classification across time (Lahey, et.al., 2005). If the group studied by James also had ADHD, and if we know that there is possible concern about stability of their ADHD symptoms that can confound sensory processing issues (if they even can be teased apart) then this causes some potential problems for the validity of sub-typing.
My interpretation of all this is that it is odd for us to be looking at the validity of sub-typing, particularly when our samples are full of children who have known sub-typing instability.
James, K. Miller, L.J., Schaaf, R, Nielsen, D. M. & Schoen, S. A. (2011). Phenotypes within sensory modulation dysfunction. Comprehensive Psychiatry, 52, 715-724.
Lahey, B. B., Pelham, W. E., Loney, J., Lee, S. S., & Willcutt, E. (2005). Instability of the DSM-IV subtypes of ADHD from preschool through elementary school. Archives of General Psychiatry, 62, 896-902.
Miller, L. J., Anzalone, M. E., Lane, S. J., Cermak, S. A. & Osten, E.T. (2007). Concept evolution in sensory integration: A proposed nosology for diagnosis. American Journal of Occupational Therapy. 61, 135-140.
Rowland, A.S., Skipper, B., Rabiner, D.L., Umbach, D.M., Stallone, L, Campbell, R.A., Hough, R.L, Naftel, A.J., Sandler, D.P. (2008). The Shifting Subtypes of ADHD: Classification depends on how symptom reports are combined. Journal of Abnormal Child Psychology,(5), 731-43.
(2010). Evolution of the sensory integration frame of reference. The American Journal of Occupational Therapy, 64(3), 363-367.
Valo, S. and Tannock, R. (2010). Diagnostic instability of DSM–IV ADHD subtypes: Effects of informant source, instrumentation, and methods for combining symptom reports. Journal of Clinical Child & Adolescent Psychology, 39(6), 749-760.