Home » IQ » Most Human Performance Traits Do Not Lie On a Bell Curve

Most Human Performance Traits Do Not Lie On a Bell Curve

Enter your email address to follow this blog and receive notifications of new posts by email.

Join 290 other subscribers

Follow me on Twitter


1050 words

Steve Sailer published an article the other day titled Wieseltier vs. “The Bell Curve” and I left a comment saying that psychological traits are not normally distributed. Two people responded to me, and I replied back but Sailer didn’t approve my two comments. I have a blog, so I can post it here.

guest says:


“We revisit a long-held assumption in human resource management, organizational behavior, and industrial and organizational psychology”

Maybe instead debunking allegedly long-held assumptions they should Notice that none of those disciplines actually exists.

They do actually exist.

Human resource management: Human Resource Management (HRM) is the term used to describe formal systems devised for the management of people within an organization. The responsibilities of a human resource manager fall into three major areas: staffing, employee compensation and benefits, and defining/designing work.

Organizational behavior: “the study of the way people interact within groups. Normally this study is applied in an attempt to create more efficient business organizations. The central idea of the study of organizational behavior is that a scientific approach can be applied to the management of workers.

Industrial and organizational psychology: “This branch of psychology is the study of the workplace environment, organizations, and their employees. Technically, industrial and organizational psychology – sometimes referred to as I/O psychology or work psychology – actually focuses on two separate areas that are closely related.

O’Boyle Jr and Aguinis (2012) write:

We conducted 5 studies involving 198 samples including 633,263 researchers, entertainers, politicians, and amateur and professional athletes. Results are remarkably consistent across industries, types of jobs, types of performance measures, and time frames and indicate that individual performance is not normally distributed—instead, it follows a Paretian (power law) distribution. Assuming normality of individual performance can lead to misspecified theories and misleading practices. Thus, our results have implications for all theories and applications that directly or indirectly address the performance of individual workers including performance measurement and management, utility analysis in preemployment testing and training and development, personnel selection, leadership, and the prediction of performance, among others.

Even most types of job performance and performance measures don’t fit a normal curve.


You say, “…psychological traits aren’t normally distributed.”

But the abstract you linked says,

individual performance is not normally distributed.

Yes, those of us who have had the misfortune to manage work groups know all about 80/20. This is performance, not “psychological traits.”

Psychological tests aren’t a measure of performance? Traits like IQ only show a normal distribution because the normal distribution is built into the tests (see below).

The other one linked says,

… at many physiological and anatomical levels in the brain, the distribution of numerous parameters is in fact strongly skewed . . .

Okay. The cylinders in the straight-six engine of my BMW lean over to one side, but that doesn’t seem to effect the horsepower. This is a physical trait.

So, what of those “psychological traits”? Like IQ? Granted, it is a kind of performance, one of taking IQ tests, but the results have a normal distribution, and it’s not the kind of performance being measured in the study referenced anyway. IQ, by definition, is a “psychological trait,” and it has a normal distribution.

IQ tests have been constructed so that the scores will exhibit a bell curve distribution. That is, the tests themselves are constructed to reveal differences that are already presumed. IQ tests are constructed with the assumption that the scores are normally distributed, however, the normal distribution is built into the test. Items that 50 percent of the testees get right are kept, along with the smaller proportion of items that many testees get right. (See Richardson, 2002 for more information.) Even most psychological constructs are not normally distributed. This is like g being supposedly physiological when—if it were—it wouldn’t mimic any known physiologic process in the body.

Buzsaki and Muzuseki (2014) review data that sensory acuity, reaction time, memory word usage and sentence lengths are not normally distributed. Basic physiologic processes, too, are not normally distributed, like visual acuity, resting heart rate, metabolic rate, etc. And this makes sense, because those traits are crucial to human survival and therefore need to be malleable. Hormones raise, for instance, during a life-or-death situation, and that is what is needed for survival. So, therefore, few physiological traits are normally distributed.

Honestly, I don’t know what your point is, but I don’t disagree with what you have shown me. I know it’s true, but I’m just too far left on your ski jump curve of losers to grasp why you responded to me that way.

Wieseltier was referring to The Bell Curve, in which results have a normal distribution.

Rigbt, the IQ book. But tests are constructed with the assumption of a normal distribution, but psychological traits are not normally distributed. Read Mizsukei and Buzsaki’s work.

Burt (1967) writes:

A detailed analysis of test results obtained from a large sample of English children (4,665 in all), supplemented by a study of the meagre data already available, demonstrates beyond reasonable doubt that the distribution of individual differences in general intelligence by no means conforms with strict exactitude to the so-called normal curve.

In sum, IQ tests are constructed with the assumption that whatever is being tested lies on a bell curve. Clearly, since they are constructed in such a way, the results are forced to fit a normal distribution. But, as seen above, most traits that are critical to survival are not normally distributed, so why should intelligence/IQ be the same? The data from Buzsaki and Mizuseki (2014) show that “skewed … distributions are fundamental to structural and functional brain organization.

(Also read The Myth of the Bell Curve and The Unicorn, The Normal Curve, and Other Improbable Creatures. where Micceri shows that achievement measures in “language arts, quantitative arts/logic, sciences, social studies/history, and skills such as study skills grammar, and punctuation” are not normally distributed. Human performance does not follow a bell curve. Also read The Bell Curve Is A Myth — Most People Are Actually Underperformers. The Bell Curve in Psychological Research and Practice: Myth or Reality?: “If IQ scores distribute normally, this does not mean that intelligence equally distribute normally in the population.” … “ In this way, a normal distribution in summated test scores, for example, would be seen as the sign of the presence of an error sufficient to give scores the characteristic bell shape, not as the proof of a good measurement.“)



  1. meLo says:

    Off topic RR and I still plan to respond to some other posts but for now I wanted to share this with you.

    Remember when Manger stated cetacean brains are only big for thermoregulation? Well some counter studies by Marino have been posted


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Please keep comments on topic.

Blog Stats

  • 863,398 hits
Follow NotPoliticallyCorrect on

suggestions, praises, criticisms

If you have any suggestions for future posts, criticisms or praises for me, email me at


%d bloggers like this: