Personality testing has grown into a major industry and is standard procedure in leadership and management courses, as part of job-interview processes, and, increasingly, in career counselling. But should we really trust such tests to deliver scientific, objective truth?

I have some bad news for you: Even the most sophisticated tests have considerable flaws. Take the Myers-Briggs Type Indicator (MBTI), the world's most popular psychometric test, which is based on Jung's theory of personality types. Over two million are administered every year. The MBTI places you in one of 16 personality types, based on dichotomous categories such as whether you are an introvert or an extrovert, or have a disposition towards being logical or emotional (what it calls "thinking" and "feeling").

The interesting -- and somewhat alarming -- fact about the MBTI is that, despite its popularity, it has been subject to sustained criticism by professional psychologists for over three decades. One problem is that it displays what statisticians call low "test-retest reliability." So if you retake the test after only a five-week gap, there's around a 50% chance that you will fall into a different personality category compared to the first time you took the test.

A second criticism is that the MBTI mistakenly assumes that personality falls into mutually exclusive categories. You are either an extrovert or an introvert, but never a mix of the two. Yet most people fall somewhere in the middle. If the MBTI also measured height, you would be classified as either tall or short, even though the majority of people are within a band of medium height.

The consequence is that the scores of two people labelled "introvert" and "extrovert" may be almost exactly the same, but they could be placed into different categories since they fall on either side of an imaginary dividing line.

One other thing, and this matters especially for anybody who thinks personality tests can guide them to a perfect career. According to official Myers-Briggs documents published by its exclusive European distributor, the test can "give you an insight into what kinds of work you might enjoy and be successful doing." So if you are, like me, classified as INTJ (your dominant traits are being introverted, intuitive, and having a preference for thinking and judging), the best-fit occupations include management consultant, IT professional, and engineer.

Would a change to one of these careers make me more fulfilled? Unlikely, according to psychologist David Pittenger, because there is "no evidence to show a positive relation between MBTI type and success within an occupation … nor is there any data to suggest that specific types are more satisfied within specific occupations than are other types." Pittenger advises "extreme caution in [the MBTI test's] application as a counselling tool." Then why is the MBTI so popular? Its success, he argues, is primarily due to "the beguiling nature of the horoscope-like summaries of personality and steady marketing."