The Flaw of Averages

    How many people really are “average”? Is it possible to design a system to fit the average person, and if not, what’s the alternative? A recent article published on examines this question, excerpting the work of L. Todd Rose from his recent book The End of Average. Rose’s narrative is somewhat massaged, but the central thesis about averages and their relationship (or lack thereof) to the individual user is well-developed and quite pertinent. We will explore these ideas through excerpts from the article, beginning with the one below:

    Back in 1926, when the army was designing its first-ever cockpit, engineers had measured the physical dimensions of hundreds of male pilots … and used this data to standardize the dimensions of the cockpit. For the next three decades, the size and shape of the seat, the distance to the pedals and stick, the height of the windshield, even the shape of the flight helmets were all built to conform to the average dimensions of a 1926 pilot.

    [In the late 1940s] military engineers began to wonder if the pilots had gotten bigger since 1926. To obtain an updated assessment of pilot dimensions, the air force authorized the largest study of pilots that had ever been undertaken. In 1950, researchers at Wright Air Force Base in Ohio measured more than 4,000 pilots on 140 dimensions of size, including thumb length, crotch height, and the distance from a pilot’s eye to his ear, and then calculated the average for each of these dimensions. Everyone believed this improved calculation of the average pilot would lead to a better-fitting cockpit and reduce the number of crashes — or almost everyone. One newly hired 23-year-old scientist had doubts.

    Before the second half of the 20th Century, as well, this philosophy dominated firearms design. Weapons were typically produced with one gunstock length or grip size, created with some rough approximation of the “average” user in mind. Of course, in reality, these were a poor fit for many people, and a very good fit for only a scant few. A different type of thinking was needed.

    It was not the first time Daniels had measured the human body. [His] field focused heavily on trying to classify the personalities of groups of people according to their average body shapes — a practice known as “typing.” For example, many physical anthropologists believed a short and heavy body was indicative of a merry and fun-loving personality, while receding hairlines and fleshy lips reflected a “criminal type.”

    Daniels was not interested in typing, however. Instead, his undergraduate thesis consisted of a rather plodding comparison of the shape of 250 male Harvard students’ hands. The students Daniels examined were from very similar ethnic and socio-cultural backgrounds (namely, white and wealthy), but, unexpectedly, their hands were not similar at all. Even more surprising, when Daniels averaged all his data, the average hand did not resemble any individual’s measurements. There was no such thing as an average hand size. “When I left Harvard, it was clear to me that if you wanted to design something for an individual human being, the average was completely useless,” Daniels told me.

    So when the air force put him to work measuring pilots, Daniels harboured a private conviction about averages that rejected almost a century of military design philosophy. As he sat in the Aero Medical Laboratory measuring hands, legs, waists and foreheads, he kept asking himself the same question in his head: How many pilots really were average?

    The bit about hand size, particularly, should be loudly ringing bells through the collective heads of all my readers. None of the hands Daniels measured conformed to the average, so then what is the use of designing for the average hand?

    He decided to find out. Using the size data he had gathered from 4,063 pilots, Daniels calculated the average of the 10 physical dimensions believed to be most relevant for design, including height, chest circumference and sleeve length. These formed the dimensions of the “average pilot,” which Daniels generously defined as someone whose measurements were within the middle 30 per cent of the range of values for each dimension. So, for example, even though the precise average height from the data was five foot nine, he defined the height of the “average pilot” as ranging from five-seven to five-11. Next, Daniels compared each individual pilot, one by one, to the average pilot.

    Before he crunched his numbers, the consensus among his fellow air force researchers was that the vast majority of pilots would be within the average range on most dimensions. After all, these pilots had already been pre-selected because they appeared to be average sized. (If you were, say, six foot seven, you would never have been recruited in the first place.) The scientists also expected that a sizable number of pilots would be within the average range on all 10 dimensions. But even Daniels was stunned when he tabulated the actual number.


    Out of 4,063 pilots, not a single airman fit within the average range on all 10 dimensions. One pilot might have a longer-than-average arm length, but a shorter-than-average leg length. Another pilot might have a big chest but small hips. Even more astonishing, Daniels discovered that if you picked out just three of the ten dimensions of size — say, neck circumference, thigh circumference and wrist circumference — less than 3.5 per cent of pilots would be average sized on all three dimensions. Daniels’s findings were clear and incontrovertible. There was no such thing as an average pilot. If you’ve designed a cockpit to fit the average pilot, you’ve actually designed it to fit no one.

    And the world’s engineers and designers wept. There was no easy answer, no real “average”; not even a large body of people who were even roughly-speaking “average-sized”, even in only a few dimensions. It was and is impossible to force every potential user to conform to an arbitrary “average” measurement, so instead engineers had to adapt to the users, and develop a new type of fit.

    By discarding the average as their reference standard, the air force initiated a quantum leap in its design philosophy, centred on a new guiding principle: individual fit. Rather than fitting the individual to the system, the military began fitting the system to the individual. In short order, the air force demanded that all cockpits needed to fit pilots whose measurements fell within the 5-per-cent to 95-per-cent range on each dimension.

    When airplane manufacturers first heard this new mandate, they balked, insisting it would be too expensive and take years to solve the relevant engineering problems. But the military refused to budge, and then — to everyone’s surprise — aeronautical engineers rather quickly came up with solutions that were both cheap and easy to implement. They designed adjustable seats, technology now standard in all automobiles. They created adjustable foot pedals. They developed adjustable helmet straps and flight suits.

    In the firearms world today, we have adjustable stocks, grips, sights, optics, cheekpieces, and most other accessories. The gun world has, wisely, adapted to the needs of the decidedly non-average user. The days of “one-size-fits-all” are not quite gone, but they are going quickly, and it’s to the great benefit of the company who can afford it to adapt their existing designs to be able to adjust even further to fit ever more perfectly every possible user – in other words, customer – who might benefit from it.

    If I may extend the topic past its welcome, it’s this quality that I would identify as one of the key factors in the popularity of the AR-15 rifle, especially since the advent of the M4 Carbine. The adjustable buttstock and the general modularity with regards to optics, grips, and handguards means that any given buyer of an M4-style weapon will get the absolute most out of it in terms of accuracy, ease of use, and speed. The more people can use the weapon to its greatest effect, the more satisfied customers a company will have, and perhaps more importantly, the fewer unsatisfied customers there will be.

    The FBI, too, has recognized this need, as its latest solicitation for a 9mm handgun requires that submissions must have frame sizes that accommodate all of three different hand sizes. Even the US Army has recognized the reality of this problem, and a major criteria in its Modular Handgun System program is that the new pistol must have interchangeable, adaptable backstraps to fit multiple hand sizes.


    Nathaniel F

    Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. He can be reached via email at [email protected]