History. Did any other events occur outside of the practice setting during the time of the practitioner–client contacts that may be responsible for the particular outcome? Since single-system designs...

History. Did any other events occur outside of the practice setting during the time of the practitioner–client contacts that may be responsible for the particular outcome? Since single-system designs by definition extend over time, there is ample opportunity for such extraneous events to occur. Example: During the course of marital therapy, Andrew loses his job while Ann obtains a better position than she had before. Such events, though independent of the therapy, may have as much or more to do with the outcome than did the therapy.