The next time you apply for a job, you may well be asked to take a personality test - even though the companies that make the tests often discourage their use for staff selection. The business of personality is big and growing. But do the tests work?
A few years back, my niece Andrea was looking for a summer job to pay her way through college.
She heard the tips were good on a riverboat restaurant in Chicago, but before the interview, she had to fill out an online application including a psychometric assessment.
"There was a whole section on ethics and how you'd react in a given situation, like dealing with an obnoxious customer", she says. "The message was pretty clear - if you're a grumpy type, don't be a waitress."
Andrea was surprised, but was faced with a similar test when she applied to work in a bookshop. Personality assessments are now ubiquitous. In a global recession, many firms want to hedge their bets and cannot afford to pick the wrong people.
Tighter profit margins also mean working under more stress and companies want to make sure their employees get on. Disagreements are costly and inefficient.
In the US alone, there are about 2,500 personality tests on the market. One of the most popular is called the Myers-Briggs Type Indicator or MBTI. Used by 89 of the Fortune 100 companies, it has been translated into 24 languages and has been adopted by governments and military agencies around the world.
"Myers-Briggs is the most successful psychometric out there and deservedly so," says Rachel Robinson of the consultancy firm YSC in central London.
"It has been a fantastic vehicle for people to think about themselves and how others are different."
Perhaps its attraction lies in its seductive simplicity - according to the MBTI, we all conform to one of 16 character types.
But that simplicity is precisely what makes some people sceptical, or even suspicious.
"There is something about the wish to put everything in neat little boxes so that we can manipulate them and make them serve our purposes that is quintessentially corporate America," says American author Annie Murphy Paul.
Her 2006 book, The Cult of Personality, claims personality tests are leading us to miseducate our children, mismanage our companies and misunderstand ourselves.
Like many personality tests, MBTI is based on the work of Carl Jung, the Swiss psychiatrist who, together with Sigmund Freud, laid the foundations of modern psychology. Jung developed the idea of opposed pairs of character traits which are present in all of us and suggested that in each pair we each have a natural preference.
It came into being thanks to an awkward relationship between a woman and her future son-in-law. Katherine Briggs, a wealthy housewife from Washington DC, realised Clarence Myers was a good catch when her daughter Isabel brought him home from college. He seemed like a nice young man, but his way of thinking was so alien to her that she turned to books for help.
Jung's Psychological Types fascinated her and became what she described as her "Bible". Soon, Isabel was infected by her mother's enthusiasm. Over two decades, the pair became avid "type watchers".
Jung only identified eight personality types, but Isabel Briggs Myers eventually doubled that number. Everybody can be described by four letters chosen out of a total of eight, she says.
To the uninitiated, it can look a bit like alphabet soup, but the first category is relatively straightforward - are you E or I? Extrovert or Introvert? The second is a choice between S or N - Sensing or Intuitive - which means some interpret the world by collecting data through their senses, others make intuitive leaps.
Then are you predominantly a T or and F? A thinker or somebody more governed by their feelings? And, finally, are you J or P? According to the blurb in the booklet, Judging types prefer to "regulate and manage their lives" whereas Perceivers favour spontaneity.
There are plenty of websites devoted to pigeonholing celebrities. Apparently, Shakespeare was an INFP and Margaret Thatcher is listed as an ENTJ. The Queen, "data driven" Condoleezza Rice and the "information carnivore" Hillary Clinton are all ISTJs.
Madonna's rebellious streak and talent for self-promotion makes her an ESTP. Jung may have dismissed such classification as "nothing but a childish parlour game" but I was curious to discover my four letters.
I completed the test online, going through the questions quickly, as instructed. But some stripped of context, seemed meaningless. What do you prefer? Hard or Soft? Spire or Foundation? Justice or Compassion?
Then I met Alice King, an occupational psychologist who works for the company responsible for Myers Briggs products in the UK. Over coffee in the British Library, she pulled a thick folder of papers out of her bag.
"Some people like the analogy of the Harry Potter sorting hat, because it can take a while to find your type."
At JK Rowling's fictional school for magicians, the enchanted hat does all the hard work and decided which house suits each pupil, but Alice wanted me to read the booklet, work through the dichotomies one by one and try to assess myself. (Rowling, like Shakespeare, is supposedly an INFP.)
"For example, both an introvert and an extravert may like going jogging after work", she said. "But while the extrovert notices people in the park as he runs past them, the introvert's energy is turned inwards. He uses the time outside to mull over ideas and what has happened that day."
After two hours, she finally revealed that I was an ENTP - Extrovert, Intuitive, Thinking and Perceiving. That puts me in the same category, some would say, as Voltaire and Machiavelli.
I guess I am an extrovert, not because I like dancing on tables but because I often get my energy from the people around me. Coming from a large family, I am used to noisy groups, and in the office I am easily distracted by phone calls although perhaps that is not because of my E characteristic so much as my WAB or Work Avoidance Behaviour (an acronym that has nothing to do with Myers-Briggs).
But I was much less convinced by the next two letters. As a reporter, I believe that I am a Sensing type. An S. In my job I look for concrete information that can be verified. Yet according to my questionnaire result, I was the opposite. An Intuitive. An N. Much as I would like to be a big picture person, I know I often get too interested in the trees and forget about the wood.
I was most surprised though by the third letter, T, which classified me as a thinker rather than an F, a feeling person. Maybe I am not as empathetic as I thought I was…
Apparently the overwhelming majority of the 2.5 million Americans who take the MBTI assessment each year feel their results do fit their personalities.
On the other hand, according to the author Annie Murphy Paul, as many as three-quarters of test takers achieve a different personality type when tested for a second time. She argues that the 16 distinctive types described by the Myers-Briggs have no scientific basis whatsoever.
The only letter I felt really confident about was the last one, P, because I do prize spontaneity and flexibility. Unlike my husband and many of my colleagues who are Js, I'm not keen on plans and timetables.
But if I were applying for a job where I knew they needed a good organiser, I might be tempted to answer differently.
Employees often sense that management is looking for a particular type for a specific post. A Sydney- based executive who used to work for an international bank, admitted to cheating on the test at the start of her career when she was desperate for promotion.
"I don't believe that corporations value diversity and I wanted to be a senior manager," she said. "I knew they wanted either an ESTJ or an ISTJ and I am an ENTJ so it didn't take a lot to fiddle with the answers. But I was conscious that I was doing it."
The investigative writer and self-proclaimed "myth buster by trade" Barbara Ehrenreich, who has been a strong critic of personality testing for years, thinks employers have a greater tendency to worry about whether a candidate is I or E, than P or J.
"You will be told that no one type is better than another and you should be spontaneous in answering the questions," she says.
"But, in reality, they are not looking for introverts. Even if what you are doing is looking at figures all day. They want everyone in the environment to be perky and positive and upbeat at all times."
According to Susan Cain's recent bestseller, Quiet: The Power of Introverts In a World That Can't Stop Talking, introverts are just as high achievers.
Yet these days more employees are expected to work in teams - to "groupthink" to use the jargon - and possibly communicate effectively with people on the other side of the world whom they have never met. There is a perception that extroverts are better at this.
The Myers Briggs Foundation discourages the use of the test for hiring and firing, seeing it primarily as a means of getting employees to think about how they interact with colleagues and work as a team.
"We don't like its use for selection because it's not an assessment of skills and abilities," says Jeff Hayes from the San Francisco-based Myers-Briggs publishing company, CPP.
"But we can't police that in every circumstance because it is used all over the world."
But as my niece Andrea knows, personality tests are used to select staff, even waitresses and bookshelf stackers.
Incidentally, she took neither of those jobs, opting for some paid research at university instead.
"The riverboat restaurant seemed more concerned with vindictive, easily annoyed, angry personality traits," she says. "Whereas the bookstore seemed mainly concerned with personalities that handle boredom and monotony well."
But that reminds me of one of my own techniques for assessing personality - I find the way someone treats a waiter or waitress surprisingly revealing. People who click their fingers or don't bother to even look at the person bringing them their food should be given a wide berth.
Lucy Ash presents The Business of Personality on BBC World Service on Sunday 8 July, at 09:05 BST