Personality tests are just one type of psychological evaluation. They can be highly specialized, and are used in many disciplines, from clinical or therapeutic to professional settings. Personality tests fall into two general types: projective and objective.
Projective tests present test takers with some kind of stimulus that is open to interpretation, like ink blots, to gauge their subjective reaction. The Thematic Apperception Test and Holtzman Inkblot Test fall into this category. Objective tests are standardized assessments that attempt to avoid responder bias and subjectivity. They're typically multiple-choice assessments that collect the test taker's responses to certain situations or concepts. So, a person's responses are subjective, but the test taker's resulting score or classification is not. Personality inventories, where people respond to statements as "true" or "false," or rate the accuracy of a statement on a scale, are common objective tests. The Basic Personality Inventory and MBTI are examples of objective tests.
The majority of personality tests psychologists use cover five general traits, or the Big Five: extraversion, agreeableness, openness to experience, conscientiousness and neuroticism. Some tests may call these traits by different names, or focus on one or two traits more than the others. Some break these five traits into smaller subtraits, or divide the traits differently (for instance, HEXACO's honesty-humility factor is part of the agreeableness factor in other tests). Some of the more well-known Big Five (or five-factor model) personality tests include the NEO Personality Inventory, 16pf Questionnaire, the Holland Codes (RIASEC), the Minnesota Multiphasic Personality Inventory and the HEXACO Personality Inventory.
Some tests, like the Levenson Self-Report Psychopathy Scale, can help detect potential mental illness, or help researchers understand how certain people react in unusual ways. Psychologists can use others, like the Beck Depression Inventory, to determine the severity of their patients' mental health issues. Some evaluations are used simply to gain personal insight about a person's behavior.
To determine whether a psychological test produces meaningful measurements, psychologists look for two factors: validity (Do the results accurately reflect the person who took the test?) and reliability (Does the same test given to the same person at different times produce the same result?). Tests that depend on self-reporting are vulnerable, to some extent, of being consciously "gamed" to achieve a certain result. But personality tests tend to ask similar questions worded differently or approaching the same concept from a different angle, partly to help weed out random or intentionally deceptive answers, partly to develop a better statistical picture of the responses. And there are methods to correct for faking responses in self-report tests, like warning respondents that faking can be detected and statistical modeling, although they have varying effectiveness [source: Fan et al.].
A wealth of different personality tests with varying credibility exist, and detailing them all would be difficult. But the Myers-Briggs Type Indicator is the most well-known by far, and we'll focus on it as the epitome of the personality test industry. Consulting Psychologists Press (CPP) has held the publishing rights for the test since 1975, and under that company's guidance, the MBTI has become a multimillion dollar industry. To find out more about the MBTI, we took it and had a CPP trainer help evaluate our results.