According to Anastasi and Urbina, psychological tests involve observations made on a "carefully chosen "sample" authors of an individual's behavior." A psychological test is often designed to measure unobserved constructs, also known as latent variables. Psychological tests can include a series of tasks or problems that the respondent has to solve. Psychological tests can include questionnaires and interviews, which are also designed to measure unobserved constructs. Questionnaire- and interview-based scales typically differ from psychoeducational tests, which ask for a respondent's maximum performance. Questionnaire- and interview-based scales, by contrast, ask for the respondent's typical behavior. Symptom and attitude tests are more often called scales. A useful psychological test/scale must be both valid (i.e., there is evidence to support the idea that the test or scale measures what it is purported to measure and "how well it does so") and reliable (i.e., internally consistent or give consistent results over time, across raters, etc.).