Based on multiple analyses of research in counseling and psychotherapy, Lambert and colleagues (Asay & Lambert, 1999; Lambert & Ogles, 2004) concluded that effective outcomes result primarily from the operation of four “common factors” of change. These factors, and their percentage of contribution to successful outcomes, are as follows:

Client factors (accounting for 40% of change): Everything that the client brings to counseling—strengths, interests, perceptions, values, social supports, resilience, and other resources
Relationship factors (accounting for 30% of change): The client’s experience of respect, collaboration, acceptance, and validation from the counselor
Hope factors (accounting for 15% of change): The client’s positive expectancy and anticipation of change
Model/technique factors (accounting for 15% of change): The counselor’s theoretical model and intervention techniques