Psychological testing is the administration of psychological tests, which are designed to be “an objective and standardized measure of a sample of behavior”. The term sample of behavior refers to an individual’s performance on tasks that have usually been prescribed beforehand. The samples of behavior that make up a paper-and-pencil test, the most common type of test, are a series of items. Performance on these items produce a test score. A score on a well-constructed test is believed to reflect a psychological construct such as achievement in a school subject, cognitive ability, aptitude, emotional functioning, personality, etc. Differences in test scores are thought to reflect individual differences in the construct the test is supposed to measure. The science behind psychological testing is psychometrics.
A psychological test is an instrument designed to measure unobserved constructs, also known as latent variables. Psychological tests are typically, but not necessarily, a series of tasks or problems that the respondent has to solve. Psychological tests can strongly resemble questionnaires, which are also designed to measure unobserved constructs, but differ in that psychological tests ask for a respondent’s maximum performance whereas a questionnaire asks for the respondent’s typical performance. A useful psychological test must be both valid (i.e., there is evidence to support the specified interpretation of the test results) and reliable (i.e., internally consistent or give consistent results over time, across raters, etc.).
It is important that people who are equal on the measured construct also have an equal probability of answering the test items correctly. For example, an item on a mathematics test could be “In a soccer match two players get a red card; how many players are left in the end?”; however, this item also requires knowledge of soccer to be answered correctly, not just mathematical ability. Group membership can also influence the chance of correctly answering items (differential item functioning). Often tests are constructed for a specific population, and this should be taken into account when administering tests. If a test is invariant to some group difference (e.g. gender) in one population (e.g. England) it does not automatically mean that it is also invariant in another population (e.g. Japan).
Psychological assessment is similar to psychological testing but usually involves a more comprehensive assessment of the individual. Psychological assessment is a process that involves checking the integration of information from multiple sources, such as tests of normal and abnormal personality, tests of ability or intelligence, tests of interests or attitudes, as well as information from personal interviews. Collateral information is also collected about personal, occupational, or medical history, such as from records or from interviews with parents, spouses, teachers, or previous therapists or physicians. A psychological test is one of the sources of data used within the process of assessment; usually more than one test is used. Many psychologists do some level of assessment when providing services to clients or patients, and may use for example, simple checklists to osis for treatment settings; to assess a particular area of functioning or disability often for school settings; to help select type of treatment or to assess treatment outcomes; to help courts decide issues such as child custody or competency to stand trial; or to help assess job applicants or employees and provide career development counseling or training