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When It Comes to Personality Tests, a Dose of Skepticism Is a Good Thing

Can you trust in horoscopes, or even personality tests?

Key points

  • The Barnum effect refers to a phenomenon where people tend to believe any statements about themselves that seem to come from a reputable source.
  • People fall for the Barnum effect partly because its statements are vague enough to apply to anyone.
  • Ways to avoid getting duped by the Barnum effect include reading between the lines.

Though incorrectly ascribed to showman P.T. Barnum, the phrase "There's a sucker born every minute" gave rise to one of psychology's favorite magic tricks. Simply put, people will believe any vague, generic set of personality descriptions of themselves if it appears that those descriptions come from a reputable source. Actually, the apparent source doesn't even have to be that reputable, though tests falsely labeled scientifically valid tend to produce a stronger effect.

If you don't have one of those at your disposal, you can still see the effect with horoscopes and fortune cookies. In the true Barnum effect experiment, subjects take a bogus personality test that produces a set of vague and even self-contradictory statements such as, "You can be outgoing at times but at times you can also be shy." When put in the correct context people will say that this analysis captures them to a "T."

There's no way to disagree with a Barnum-type assessment, but hardly anyone ever perceives how silly it is, especially if they've just answered a 25-item personality "test" that they are told will provide unique insights into their innermost qualities. Only when the deception is pointed out do most people realize that they were suckered into believing this false analysis.

It's odd in a way that the effect which in itself is based on stretching the truth is itself based on a misquote. Leaving irony aside for the moment, let's see what's going on with the Barnum effect. Later, I'll talk about how you can avoid becoming a sucker yourself.

Why people fall for the Barnum effect

One reason that people fall for the Barnum effect is that the feedback given in the typical experiment is so generally worded that there's practically nothing to disagree with. The statements are phrased in terms of two diametrically opposed possibilities: "you can be both X and Y" (or sometimes, X "but" Y).

Almost anyone can be anything under the right circumstances especially when the Xs and Ys are vague enough to capture any human quality. "You can be smart but at other times you can be dumb." That's true of every human on the planet; even Einstein would have agreed with this self-assessment.

Psychics at times will use such statements at what they call cold readings in which they know absolutely nothing about you and so they start with something you'll definitely agree to be true. Here's one I picked up from the Skeptic's dictionary: "At times you are extroverted, affable, sociable, while at other times you are introverted, wary and reserved." This is pretty much straight from a Barnum effect script in a psych experiment.

The second reason people fall for the Barnum effect applies more to predictions about the future, the ones we find in fortune cookies and horoscopes. These provide a comforting, if not always reassuring, sense of control over the unknown. In our constant struggle to see into the unknown, these vapid pronouncements give us a handle with which we can open the door. No matter that it's not going to be a very clear view, nor that if we were keeping records, we'd realize that these prognostications were completely off-base. For that minute or two that you think it over, it's going to make you think that you'll know what to look out for in the next 24 or so hours.

Of course, the writers of these homilies are smart enough to know that if they broaden the net widely enough, pretty much everything that happens to the reader will happen. Here's one I found for myself, from yesterday: "You're more in the mood to listen than to speak up now — so make sure that you're surrounded by the right people. They've got plenty to say, and you might learn quite a lot by keeping your mouth shut." I suppose there was a two-minute period yesterday when I thought to myself that I should give the student I was advising a chance to say more. Sure, I'll buy that. Then to the test- I looked at 3 more post-horoscopes (ones from previous days), and each of them worked just fine as well.

Often people read their own meanings into Barnum-type pronouncements and this is another reason that we believe in them. If we're looking for a reason to be cheered up, we'll read the message as containing hope and if we're feeling a bit down, we may seek to confirm our worst fears.

This is what happened in mythology to King Croesus (from the phrase "rich as Croesus") in the 6th Century B.C. To guide him in his decisions, he sought the wisdom of the famous seer, the Delphic Oracle. Known for her Barnum-like predictions, she at times could be maddeningly vague. However, when he sought her prediction about the outcome of a possible battle with the Persians, he was pleased with her response: "After crossing the Halys, Croesus will destroy a great empire." Satisfied that victory would clearly be his for the asking, Croesus advanced into battle, only to suffer total defeat. It turned out that the empire he "would destroy" would be his own.

There are three reasons why the Barnum effect, as amusing as it is, has a dark side. First, there is the risk that you will throw away your money on useless mind-readings. Second, you may actually be given poor advice. If you make a life-changing decision on the basis of Barnum-type information, it won't take a fortune cookie to tell you that "bad things happen to people who believe liars." Third, you might ignore good advice if it isn't painted in glitzy packaging. The honest but perhaps boring (or unwanted) advice you get from someone close to you just might not seem as appealing as that of the supposed expert who relies on a few splashy waves of the hand.

How to avoid getting duped

Since the Barnum effect is so prevalent in our society, what steps can you take to avoid being duped? Here are four suggestions:

  1. Knowledge is power. You know that fortune cookies are written en masse and that horoscopes by definition must cover 1/12 of the population on any given day. Don't believe these obvious sources of false information.
  2. Look for evidence of validity. It probably wasn't necessary to tell you about #1 above, but here's one that really matters — psychometrically valid personality tests must go through years of rigorous screening. Those qualities called reliability and validity are essential ingredients of a good assessment tool. While it may be fun to take a self-test in a magazine, keep in mind that these not only are usually too brief to do any good but typically they have no scientific basis.
  3. Read between the lines. Look for those telltale signs that you saw in the cold psychic reading. Is a statement broad enough to encompass all people in all situations? Though it may be trumped up with official-sounding words such as "extraverted," unless you can honestly say that it wouldn't fit anyone besides you, then chances are it has a touch of the Barnum effect.
  4. Trust the professionals when it comes to important assessments. Mental health professionals receive years of training under highly supervised conditions. In order to provide assessment services, many also must become licensed. Therefore when you're about to make an important decision based on any kind of assessment, seek your input from someone with proven credentials.

The Barnum effect won't go away anytime soon. In fact, websites that can give you instant horoscopes, diagnoses, or guidelines for the future make the problem far worse. You can even download a fortune cookie Facebook application. Yes, Barnum is here to stay.

The moral of the story is that we can all be suckers — or at least some of us can some of the time.

Copyright Susan Krauss Whitbourne, Ph.D. 2010

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