Factor structure of the Motivation Assessment Scale.

The Motivation Assessment Scale (MAS) was developed to provide clinical information on four hypothesized functions that may control problem behaviour in persons with developmental disabilities. The original four-factor structure of the MAS was based on face validity, with the items being grouped in terms of each of the hypothesized functions. Validation of the scale was provided in terms of correlations between teacher ratings of eight children on the MAS and ranking of the controlling variables from functional analogue tests. In this study, staff in residential facilities rated 60 residents and teachers in schools rated 96 students on the MAS. The target behaviour rated for both samples was self-injury, with the institutional sample engaging in the behaviour more than 15 times an hour and the school sample, less than 15 times an hour. The results of factor analyses, with varimax rotation, provided a conceptually meaningful factor structure with the institutional sample, but not with the school sample. The 16 MAS items resolved into four factors that were conceptually related to four conditions that may maintain problem behaviour (i.e. sensory, escape, attention and tangible). The results suggested that the original MAS has a robust factor structure and may be clinically useful in predicting the controlling functions of problem behaviours, if the target behaviours occur at a rate no less than 15 responses per hour.