How Personality Tests Work

The earliest personality types were based on the ancient medical theory of the four humors, which posited that humans are filled with four different fluids: black bile, yellow bile, phlegm and blood. According to humorism, imbalances in these fluids caused diseases and other health problems.

Humorism tied physical, mental and emotional aspects together. So a person who had an excess of one type of humor would have a corresponding behavior and personality type. Ancient Greek physician Hippocrates refined the concept of the four humors into the theory of the four temperaments: melancholic, choleric, phlegmatic and sanguine. This concept remained popular until the 19th century, when the four humors theory was discredited by more accurate medical knowledge. The theory lives on in the English language, though — for instance, the word melancholy is derived from the Greek words for "black bile," the humor associated with depression.

Many modern personality classifications are derived from the theories of Carl Jung, who published the book "Psychological Types" in 1921 in German and 1923 in English. Jung created four categories of personality function: sensation, intuition, thinking and feeling. Each function was modified by a person's tendency to be extraverted (focused on and drawing energy from outside objects and people) or introverted (focused on their own thoughts and solitude). But Jung's personality type theories were based on his own ideas and interpretations of contemporary psychological theories, not on any empirical studies or research.

Teacher and aspiring fiction writer Katharine Cook Briggs had already been working on her own system of personality classification when she read Jung's book, and, as the corporate legend has it, threw her work into the fireplace and started over. She built on Jung's ideas, refined the categories and developed ways to determine which categories people fit best [source: Segovia]. She also stripped away certain aspects of his theory, like his concepts of the unconscious. Briggs worked on her personality theories with her daughter, Isabel Briggs Myers, for decades, writing out questions and categories on index cards [source: Cunningham]. Women's sudden entrance into the workplace during World War II pushed Myers and Briggs to figure out how to use personality type to determine what jobs women might do best or prefer. The test the mother-daughter duo developed eventually became the Myers-Briggs Type Indicator.

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.

The Myers-Briggs Type Indicator sorts people into one of 16 different personality types by determining which side of four type pairs ("dichotomies") they fall on. Each attribute is represented by a letter, so someone who's familiar with the MBTI might say she's an ISTJ, and their co-worker is an ENFP.

The four pairs are:

Each category, or psychological preference, describes the way a person prefers to interact with the world, and doesn't always match the common definition of the word. We discussed extraversion and introversion earlier, in relation to Jung's psychological types theory. Sensing is a preference for empirical, direct information and data, while intuition is more of a "big picture," go-with-your-gut preference. Thinking people are more focused on logic and objectivity, while feeling people put more value on relationships and social harmony. Judging is a preference for schedules and decisiveness, while perceiving is a preference for a go-with-the-flow, adaptable attitude.

To sort you into the categories, the MBTI asks a series of questions, such as "When you go on a trip, do you want everything planned out in advance, or would you rather take each day as it comes and do whatever you feel like?" It also presents word pairs (i.e., "schedule — freedom" and "compassion — foresight"), and asks test takers to choose which word they like better.

Normally, taking the official MBTI costs about $50, and taking it with an hour of feedback from an MBTI professional will set you back $150. A career report tacks on another $16.95. Attending an MBTI class, having on-site training or being certified in MBTI will cost about $1,500 or more, depending on how far you want to go into the teachings [source: The Myers & Briggs Foundation].

CPP let us take the MBTI for free, and MBTI Certification Programs lead trainer Michael Segovia walked us through our results. Segovia made it clear that the categories simply represent preferences, and that everyone can and does use the opposite category in their lives. In fact, the Myers & Briggs Foundation site states that the person taking the test is the expert, and the only one who truly knows which type fits them. CPP used the metaphor of handedness — it feels more comfortable to sign your name with your dominant hand, but you technically can sign with your nondominant hand if you need to. In fact, Segovia had me do this exercise, signing my name with one hand and then the other, during our phone interview.

The MBTI emphasizes the dynamics between different types, and how they might affect happiness or performance in the workplace. People could also consider the preferred type in their culture, and how that affects their interaction with the world. For instance, the U.S. business world places a lot of value on being a "J" (judging, or favoring schedules and precision), so a lot of American professionals with a natural preference for "P" (perceiving) might struggle to accommodate the demands of their workplace. But the preferences are not hard-and-fast rules. "The Myers-Briggs assessment suggests predisposition, but not predetermination," Segovia said in an email. "Rather than pigeonholing, it empowers individuals to further shape their futures through an understanding of their own preferences and those of others."

But the MBTI has plenty of skeptics and detractors, who cite several well-documented flaws of the assessment.

Psychologists, especially in the academic world, direct a fair amount of criticism toward the MBTI and similar personality tests. The most common criticisms include:

These shortcomings affect other self-report tests and personality inventories that are based on the same model as the MBTI. Generally, psychologists view Big Five personality tests as more reliable. But CPP, the publisher of the Myers-Briggs Type Indicator, has some rebuttals to these criticisms.

There are also concerns regarding how personality tests are used in the real world. Responding to worries that MBTI results are used to hire, fire or promote employees, Segovia said, "The MBTI tool is used to develop employees and to bring out the best performance by helping them become more self-aware, and also more aware of the differences in preferences and talents that other people bring to the table. However, it is not designed for, nor should it be used for any kind of selection (hiring, promotions, etc.)." Yet, up to 60 percent of workers are asked to take workplace tests, and many organizations even give personality assessments to job candidates [source: Meinert].

The CPP does portray the MBTI categories in a positive light — Segovia even referred to the test as a forerunner of positive psychology. All 16 types are considered equal, but some may excel at particular types of work or engage with specific personality types better. But one slightly negative perspective we found when taking the MBTI was a discussion of what might happen if a type takes a preference too far, possibly because of stress. For instance, there are many positive aspects of being an INTP, but if you're too INTP, you might be guilty of "overintellectualizing and becoming too theoretical in your explanations," as the MBTI puts it.

Regarding the validity and repeatability of the results (Jung, Myers and Briggs contended that a personality type was something you have for life), Segovia told us that different results in retakes of the assessment simply suggest that the initial response was close to the center line in the dichotomy, so a few different answers would push a person to the other side of the dichotomy. This could be easily interpreted as pointing out a major flaw in any effort to divide people into rigid categories, however — if an assessment has repeatable results, changing a small number of answers shouldn't drastically affect the outcome. Regardless, Segovia said in an email, "Test and re-test agreement for each aspect of MBTI type is nine times higher than chance, and for three of the four dimensions it is about three times higher than chance, meaning that individuals are likely to receive the same results on consecutive MBTI administrations."

So, the scientific value of personality tests is under much scrutiny, thanks to their wavering legitimacy and the ambiguity of personality itself. But personality testing is used widely, in counseling, employment, therapy and elsewhere. Despite the criticism leveled against these tests, they remain successful — and profitable.

Some companies have nixed personality tests or specific test questions, after they caused instances of discrimination or just proved ineffective. Research shows personality tests alone don't predict job performance well. But workplace personality testing is estimated to bring in $500 million annually, and the industry is growing every year [source: Weber and Dwoskin, Meinert]. Just how successful is the MBTI? Publisher CPP provided the following statistics:

CPP declined to provide any financial data, but a 2012 Washington Post article reports that the MBTI and the various materials, certifications and training sessions related to it bring in $20 million annually. It isn't just used by corporations, either: Universities and government agencies, including the Environmental Protection Agency and the Department of State, give the assessment to their employees. According to the Society for Industrial and Organizational Psychology, 13 percent of U.S. employers use personality tests.

The reasons for this widespread success include some of the very flaws critics point out. The MBTI's positivity means that no one walks away from the test feeling bad about themselves. (CPP doesn't like it to be called a test, by the way, because "there are no incorrect answers — it's an indicator," Segovia said.) There's even a name for this: the Forer effect, first described in an experiment in which students who took a personality assessment all rated the resulting identical, positive personality profiles as highly accurate descriptions of themselves. Some of the other psychometric tests that do incorporate negative elements, like five-factor model tests, are seen as more valid by psychologists, but are less popular in workplace settings. Segovia even said that asking employees about their negative traits would be unethical and overly intrusive.

The relative simplicity of putting people into categories, rather than using a sliding, continuum-based system, also contributes to the popularity of the MBTI and similar questionnaires. "People like being told what type they are. My students snooze when I talk about the Big Five and how each trait is independent, but as soon as I say INTJ they get so excited," Shulman said.