Psychotherapy research is primarily concerned with the evaluation of the impact and process of psychological interventions for clinical disorders (e.g., depression, anxiety), problems of living (e.g., marital discord), and medical conditions (e.g., chronic pain). It is also concerned with characteristics of the client and therapist as they relate to treatment process and outcome. Most psychotherapy research has focused on individual treatment. However, numerous investigations have also been conducted on couples, family, and group therapy.