Several criteria exist for defining a psychological disorder. Sometimes a person needs to meet only one criterion to be diagnosed as having a psychological disorder. In other cases, more than one of the following criteria may be met:
Example: Ted’s delusion that he is a prophet causes him to stand at street corners lecturing people about the morality of their behavior.
Example: Bethanne’s excessive use of alcohol makes her unable to hold down a job.
Example: David suffers from chronic and painful anxiety.
Psychologists use different conceptual models for understanding, describing, and treating psychological disorders.
The medical model is a way of describing and explaining psychological disorders as if they are diseases. Many terms used to discuss psychological disorders come from the medical model. Diagnosis refers to the process of distinguishing among disorders. Etiology refers to the cause or origin of a disorder. Prognosis refers to a prediction about the probable course and outcome of a disorder.
Critics argue that this model is not suitable for describing psychological problems. They say that psychological problems are not illnesses but rather behaviors and experiences that are morally or socially deviant.
The vulnerability-stress model states that psychological disorders result from an interaction between biological and environmental factors. According to this model, individuals who have a biological vulnerability to a particular disorder will have the disorder only if certain environmental stressors are present.
The learning model theorizes that psychological disorders result from the reinforcement of abnormal behavior.
The psychodynamic model states that psychological disorders result from maladaptive defenses against unconscious conflicts.
Psychologists use two methods to assess a psychological disorder: objective testing and projective testing. Objective tests are usually pencil-and-paper standardized tests such as the Minnesota Multiphasic Personality Inventory (MMPI). Projective tests require psychologists to make judgments based on a subject’s responses to ambiguous stimuli. Word association tests or the Rorschach test, in which subjects interpret a series of inkblots, are examples of projective tests. (See pages 285–287 for more information on these tests.)