It is reliable in the sense that it always measures the same thing. A test aimed at measuring a particular characteristic should measure the same person at different times.
It is valid in the sense that it measures the characteristics which the test is intended to measure. Thus, an intelligence test should measure intelligence and not simply verbal facility. (Armstrong, 2001: 473) Personality questionnaires allow quantification of characteristics that are important to job performance and difficult to measure by other methods. The debate about the value of personality tests is ongoing, and centre around lack of agreement on four key issues