Objective. We designed a simple rating instrument, the Occupational Therapy Task Observation Scale (OTTOS)^©, to facilitate evaluation and documentation of patient performance during occupational therapy task groups and to improve the communication between occupational therapists and other treatment team members.

Method. After analysis of other rating instruments, a preliminary version of OTTOS was designed, extensively field tested, and further modified. Interrater reliability was determined, and validity was tested against three established rating instruments: the Bay Area Functional Performance Evaluation, the Comprehensive Occupational Therapy Evaluation Scale, and the Milwaukee Evaluation of Daily Living Skills.

Results. The final version of OTTOS contains two parts, 10 items for evaluation of specific task functions and 5 items for rating general behavior. Field use demonstrated that the scale successfully tracked changes in functional capacity and included most facets of patient function evaluated during task groups. Use of OTTOS required minimal training, and scoring required less than 2 min for each patient. The correlation between the scores of experienced occupational therapists was high (.92 for the total scores). The correlation between OTTOS and the other rating instruments ranged from .880 to .340; the highest correlations, as expected, were with test subscales that most closely resembled OTTOS.

Conclusion. Preliminary data indicated that OTTOS offers a reliable and valid method for rapidly rating the function of patients with psychiatric illness attending task groups. In addition, use of OTTOS improved the communication between occupational therapists and other health care providers, facilitated the education of occupational therapy students, and met the documentation requirements of third-party payers.