It’s back-to-school season once again, and that of course means tests. Those of us in the testing business reminisce with fondness about school days. School may not have been much fun, actually, but at least the tests back then were blissfully simple and meaningful. Know all the state capitals? You get an “A.” Now go outside and play.

In the working world testing is more complicated. Assessments of business-related knowledge and skills aren’t really much different from that 50-states test: either you know your stuff, or you don’t. But tests that measure personality traits, while potentially extremely useful, are also much more difficult to use correctly. (Congratulations, you scored an “INTJ.” Now what?!)

The secret to success is, as you might guess, doing your homework.

Is Personality the Secret to Hiring?
There are hosts of personality tests on the market, all claiming to be helpful in making hiring decisions. But before hiring and recruiting professionals commit to using personality tests, they need to understand the difference between "causation" and "correlation." In other words, does a "good" personality score really indicate "good" performance?

Causation means that one thing causes another to happen. Throw chalk at the class bully and you can expect to be punished. The stimulus causes the punishment.

Correlation means that two things tend to occur at the same time, but one does not "cause" the other. Pocket protectors and mathematical ability are correlated (i.e., co-related), but having a pocket protector does not cause someone to be a math whiz. This is a very important thing to know (as we will see later) when using a personality test to hire someone.

Personality, Performance, and Hiring
Why do we give applicants tests? To quickly predict future performance. That is, instead of hiring someone and then waiting around a few years, we give applicants a short test, examine the score and conclude, "Aha! This score means the applicant will be our next Employee of the Month.”

Test results, however, are accurate only if the test content is associated with job performance, meaning that it has a causal link to on-the-job behavior. For example, it's "causal" when employees with bad problem-solving skills make bad decisions. It's also "causal" when those bad decisions create unnecessary expense.

Common sense tells us that when problem solving is important to job performance, a quickie test of problem-solving ability can lead to fewer mistakes, and more profits. An appropriate problem-solving test can simulate problem-solving on the job, and when properly validated, will show that high test scores predict high job performance.

But what about personality tests? What do they have to do with job performance? (Note: I use the term "personality test" to mean any kind of self-descriptive test of style, temperament, or interest).

Week after week, I see people using scores from personality-type tests to predict job success. When I ask them about causation, they look as me as if I just arrived from another planet. Then, after a long pause, I usually get three kinds of responses:

1. "Our managers like it. That's good enough for us!"
2. "We gave it to our top producers and use their scores as our answer key."
3. "Huh?"

Sigh… We will only examine responses along the lines of #2 above. Respondents #1 and #3 can try taking the test again next week, but I doubt that they’ll improve their grade.

What's a Top Producer?
This is one of those situations where common sense fails us. The term "top producers" is an attractive one, but top producers are seldom alike. For one thing, what is the definition of the word "top"? Most sales? Most repeat customers? Biggest projects? Best attendance? Most popular? Lowest golf handicap?

People are generally good at some things and poor at others. Lumping all "top producers" into the same category is like putting mixed fruit into a blender and pressing the "liquefy" button: all the individual differences disappear into mush. (Although it should be noted, some HR organizations have a taste for a nice, consistent mush.)

Therefore, the first step in using personality to predict job performance is to avoid the blender approach and carefully define the term "top.” For example: "most friendly," "most service-oriented," "best closer," "best team player.” Remember, the more explicit the performance criteria, the more accurate the study.

Some readers may now be thinking, "This is tough. How can I possibly classify top producers into similar groups?" Congratulations! You have moved one step closer to hiring enlightenment.

The Problem With Averages
Okay, we have minimized the blender approach and properly classified producers into a variety of "top" and "bottom" groups. Now we can give all top and bottom producers the personality test, average each group's scores, and compare the differences? We are done, right? Not by a long shot.

Averaging individual scores is like having one foot in a roaring hot fire and the other in freezing ice water, and concluding, on the average, that the temperature is comfortable. "Average" comparisons might seem like a good idea, but they tend to conceal extremes.

Here's an example. Take two ranges of scores for adaptability: The high group had a range of 50 to 90, with an average of 70; the low group had a range of 40 to 80, with an average of 60. There's a difference! We can use it to predict individual performance! Right? Wrong.

Yes, there is a difference based on groups. But what we care about is hiring individuals, and there is an inconvenient score "overlap" that needs explanation. Why do some individuals in the "low group" actually score higher than the "high group," and vice versa?

We have discovered correlational group differences for adaptability, but we cannot yet conclude that adaptability causes performance.

The Right Way and the Wrong Way
When we "shotgun" a personality test to employees (i.e., give everyone the test and look for patterns), we run the risk of finding garbage relationships. That is, we might find high scores in "adaptability" are common among high performers, but that might occur entirely by chance. Could shotgun studies lead to hiring mistakes?

Remember the pocket protector example? Shotgun personality results showed that pocket protectors and math nerds were correlated, so if we started hiring only applicants with pocket protectors, would we get the mathematicians we needed? In other words, will a pocket protector cause someone to become a Poindexter?

Of course not. Even if we made the pocket protector a hiring criterion, some applicants would be mathematically inclined, some merely fastidious or old-fashioned. Worse, some clever ones might just buy a pocket protector before the interview (even personality tests can sometimes be faked). This was a bad hiring criterion because it did not cause the desired correlation.

Likewise, although "adaptability" might be common among high performers, will hiring applicants based on high adaptability scores lead to better employees? How do we discover if high "adaptability" actually leads to high performance? Sharpen your pencils; it's a multiple-step process.

• We start with a clean slate.
• We interview jobholders, managers, and visionaries, asking them all kinds of questions about success and failure, listening carefully for key behaviors that sound like "adaptability."
• We carefully separate existing employees based on some form of "adaptability" rating.
• We give both high and low performers a valid and reliable personality test (i.e., one specifically designed to measure on-the-job adaptability).
• We statistically compare scores on the adaptability test with adaptability performance ratings.

If high adaptability scores correlate with high performance and low scores with low performance, then we can feel confident our adaptability test will predict job performance.

The Research
What's a good article without some homework to back it up? The research shows:

• Personality is only a good predictive factor when applicants already have the skills for the job. Think of skills and personality as two sides of a coin: One side represents the "hard skills" brought to the job ("can do"), the other, personality, represents how skills are applied ("will do").
• There are only a few personality traits that are demonstrably associated with job performance. The challenge is to find and confirm them.
• When done right, and assuming the employee also has the necessary "hard skills," having the right personality for the job really can affect productivity – by at a factor of at least two to one.