Various workshops given by Nielsen-Norman Group in the User Experience field, mention a specific experiment that involved Air Force cadets.

The experiment is meant to illustrate the point that there's no such thing as an "average user", and it goes like this:

680 Air Force cadets were lined up in a field. All were roughly the same age and within narrow height and weight limits. Then an officer called out the average size of uniform items - first underwear, then pants, shirts, etc. Everyone not wearing the average size for that particular item were dismissed and left. By the fifth item, only two cadets remained. By item six, one was left. By item seven, all were gone.

This means that out of the 680 cadets there wasn't a single one who was the average size in all uniform items.

I attended a workshop where this was claimed, and there's also a presentation online from a different workshop of theirs, where this claim can be found (slide 57 here).

However I couldn't find any other mentions of this experiment online. I wonder whether it can be just an urban legend.

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    I'd just like to add that this story shows absolutely nothing about User Experience. It's a ridiculous diversion to make you more susceptible to bullshit stories they sell you in workshops. – Davor Jun 3 '15 at 12:29
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    Yeah, I don't see what point this story would have in any context. Cadets are already a skewed sample because you have to be within a certain size range to be one. Further, once you pile on 7 or 8 different things, the number of combinations is massive. It's not really that significant that in only 680 people no one fit any given set completely. – fredsbend Jun 3 '15 at 16:52
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    @Davor It's a nice anecdote that does drive home the claim that when designing for the average user you're optimizing for noone, so that instead of having at least some users who get an optimized experience, nobody gets it. – Vitaly Mijiritsky Jun 3 '15 at 16:56
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    @VitalyMijiritsky - which is, of course, completely false in the case of software, because user experience is not made in discrete sizes like shoes. – Davor Jun 3 '15 at 19:14
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    @Davor Not as false as you may think. Users' needs, use cases, workflows and tasks can be pretty discrete and sometimes mutually exclusive, especially in enterprise settings. But I don't think that this is the place for discussing UX, you're welcome over at UX.SE if it interests you. – Vitaly Mijiritsky Jun 3 '15 at 19:21

This story is sourced to Tyler Blake, professor CSU Northridge.

The story is printed in Advances in Human-computer Interaction (1995) at page 94, and the reference for the story is given as

Blake, T. (1985). Introduction to Principles and Techniques for Interface Design Tutorial Notes for CHI'85 tutorial.

This corresponds to a tutorial by Tyler Blake from 9AM - 12:30 PM Monday 15 April 1985 as part of the Conference on Human Factors in Computing Systems, Hyatt Regency at Embarcadero Center, San Francisco. Source.

see Introduction to Principles and Techniques for Interface Design

The story is also in TOG on Interface (1992)

The older version of the story is somewhat different from the one in OP.

The original version does not include "All were roughly the same age and within narrow height and weight limits" nor "By item seven all were gone". Also, the earlier version says "shoes, pants, and shirts" instead of the "underwear" mentioned in the OP.

It makes clear that anyone not within one standard deviation of average was excluded each round.

Specifically, the original (or at least 1992) version of the story is:

Several years ago, the Air Force carried out a little test to find out how many cadets could fit into what were statistically the average-sized clothes. They assembled 680 cadets in a courtyard and slowly called off the average sizes - plus or minus one standard deviation - of various items such as shoes, pants and shirts. Any cadet that was not in the average range for a given item was asked to leave the courtyard. By the time they finished with the fifth item, there were only 2 cadets left; by the sixth, all but one had been eliminated.

Comparing the story to statistical expectations for normal distributions of independent variables:

68.2 % are within one standard deviation.

0.682^5 = 0.148 (101 / 680)

0.682^6 = 0.101 (69 / 680)

0.682^7 = 0.069 (47 / 680)

So even after 7 round, one would expect 47 cadets to be remaining, and even more given sizes of various clothing items are correlated. The story doesn't seem credible.

On the other hand, there is a study involving 680 cadets discussed in the 1955 article "Physique and success in military flying" American Journal of Physical Anthropology, vol. 13, pages 217-52. The story could have originated from actual measured data, but morphed over time.

Particularly, it seems to be a dramatization of The "Average Man"? (1952) by Gilbert S. Daniels.

The fallacy of the "average man" concept is further illustrated by a study based on body measurements made on over 4,000 Air Force flying personnel. From a total of 131 available measurements a smaller group, all useful in clothing design was selected.

  1. of the original 4063 men, 1055 were of approximately average stature

  2. of the original 1055 men, 302 were of approximately average chest circumference

  3. of the original 302 men, 143 were of approximately average sleeve length

  4. of the original 143 men, 73 were of approximately average crotch height

  5. of the original 73 men, 28 were of approximately average torso circumference

  6. of the original 28 men, 12 were of approximately average hip circumference

  7. of the original 12 men, 6 were of approximately average neck circumference

  8. of the original 6 men, 3 were of approximately average waist circumference

  9. of the original 3 men, 2 were of approximately average thigh circumference

  10. of the original 2 men, 0 were of approximately average crotch length

The article details what was considered average, basically the middle 25-30%.

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    That statistical analysis doesn't seem particularly meaningful to me. Aside from correlation, assuming 68.2% of men (even of similar age and build) wear the same size shoe doesn't seem like it comes anywhere near reality. – femtoRgon Jun 2 '15 at 18:23
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    @femtoRgon maybe my answer isn't clear enough that the original version of the story explicitly specifies that average size "plus or minus one standard deviation" was the selection criterion for each round. Only persons outside this plus or minus one standard deviation range were excluded each round. – DavePhD Jun 2 '15 at 18:31
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    You're right, I did miss that. Thanks you for clarifying. – femtoRgon Jun 2 '15 at 18:49
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    Your calculations assume independence of the various attributes (pants size, shirt size, etc), yet these tend to be correlated (they're strongly related to height and BMI for example). So you can't just take a product of probabilities and expect to get very close to reasonable approximation of their joint probability. – Glen_b Jun 3 '15 at 2:33
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    @Glen_b yes, my answer already says "even more given sizes of various clothing items are correlated". The calculation is meant only to show many more than two people would be left after round 6, and even round 7, statistically even without considering correlation. – DavePhD Jun 3 '15 at 2:36

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