1. & ( 1992). Hierarchical linear models: Applications and data analysis methods. Newbury Park: Sage.
2. , , , & ( 1995). Integra Outpatient Tracking System. Philadelphia: Integra Inc.
3. The dose–effect relationship in psychotherapy.
4. , & ( 1993). When clinical trials fail: A guide to disaggregation. In , & (Eds.), Behavioral treatments for drug abuse and dependence (NIDA Research Monograph No. 137, pp. 291–302). Washington, DC: National Institute for Drug Abuse.
5. The attrition dilemma: Toward a new strategy for psychotherapy research.