Psychotherapy is an art, they say, not a science; laboratory and survey studies capture only a small and shadowy image of the complex exchange that takes place between a therapist and a client. Scientific psychologists agree that research has little to say about the existential aims of therapy, such as helping people come to terms with illness and death or helping them choose which values to live by. But scientist are concerned that when therapists fail to keep up with empirical findings in the field-findings on the most beneficial methods for particular problems, on ineffective or potentially harmful techniques, and on topics relevant to their practice, such as memory, hypnosis, and child development-their client may pay the price. Over the years, the breach between scientists and therapists has widened on this issue of the relevance and importance of research findings, leading to what some psychologists call the scientist-practitioner gap. This gap can have powerful individual and social consequences. .
Despite the skepticism about research on the part of many clinicians, economic pressures and health costs are requiring the empirical assessment of psychotherapy. For example, consider the traditional psychodynamic assumption that the longer therapy goes on, the more successful it will be. Of course, people with severe mental disorders do often require and benefit from continued therapeutic care. About half of all people in therapy improve within 8 to 11 sessions, according to self-reports and objective measures of improvement. And 76 percent improve within six months to a year; after that, further change is minimal. To develop these guidelines, clinical researchers conduct controlled clinical trials, in which people with a given problem or disorders are randomly assigned to one or more treatment groups or to control group.