Educational and psychological assessment is one of the skills that a psychologist uses to help with the diagnosis of mental disorders and learning problems and planning interventions. Psychological testing or psychological assessment is characterized by the use of psychological measures to obtain small samples of behavior in order to infer generalizations about a given individual. A useful psychological measure is both valid (actually measures what it claims to measure) and reliable (is internally consistent or give consistent results over time). The technical term for the science behind psychological testing is psychometrics. By samples of behavior, one means observations over time of an individual performing tasks that have usually been prescribed beforehand. These samples are gathered in face to face interactions or by using self administered tests via paper/pencil or computer. Other samples are gathered from interviews with persons who know the individual being evaluated or by having those persons complete checklists or surveys about the person being assessed. These responses are often compiled into statistical tables that allow the evaluator to compare the behavior of the individual being tested to the responses of a norm group. When multiple tests are administered, the procedure is referred to as full battery assessment.