Early development of stereotyped and self-injurious behaviors: I. Incidence.

From five programs with 457 eligible children, 39 children younger than 40 months who had developmental disabilities were studied. Video sampling, observation notes, parent reports, staff reports, and clinical records were the data sources. Twenty-one children, or 4.6% of the total number in the program, exhibited SIBs. Virtually all children in the sample who were motorically capable of it showed body-rocking in at least one position. The SIBs were directed mainly toward the head, and body-rocking occurred mainly in four-point and seated position.