Psychological tests (also known as mental measurements, psychological instruments, psychometric tests, inventories, rating scales) are standardized measures of a particular psychological variable such as personality, intelligence, or emotional functioning. They often consist of a series of questions that subjects rank as true or false, or according to a Likert-type scale, however tests can use written, visual or verbal methods.
Published tests, also known as commercial tests, must be purchased, and their publishers may require proof that the users have sufficient professional credentials to administer the test. Some well-known commercial tests include the Myers-Briggs Type Indicator and the Sixteen Personality Factor Questionnaire.
Unpublished tests are not available for purchase from a publisher and can be obtained from the creator or from professional literature written by test authors.