Kasari, C., Freeman, S., & Paparella, T. (2006). Joint attention and symbolic play in young children with autism: a randomized controlled intervention study. Journal of Child Psychology and Psychiatry, 47:6, pp. 611–620.
On page 620 of the manuscript there is an Appendix B. Definition of play levels
Under the table that is Appendix B should also be:
Adapted from Lifter, K., Sulzer-Azaroff, B., Anderson, S. R., & Cowdery, G. (1993). Teaching Play Activities to Preschool Children with Disabilities: The Importance of Developmental Considerations. Journal of Early Intervention, 17, 139–159.