Are People Actually Any Good at Estimating Height?

Matthew J. Sharps

A recent criminal case of potential political importance dealt with the fact that the accused, who is reported to have fired on and wounded a victim, estimated the victim's height at approximately 6 feet. The height was in fact 5 feet 8 inches.

This case raises an interesting question in the eyewitness realm: How good are human beings at estimating dimensions?

This problem has proven potentially important in my own research. In several experiments on eyewitness cognition (summarized in Sharps, 2022), we asked witnesses to experimental crime scenes to estimate, subjectively, the heights of suspects they observed. The estimates came in; tall, medium-sized, "kind of short," whatever.

But in the same protocols, we asked for numerical estimates of suspect height as well. The estimates came in; 6 feet tall, 5'8," 5'2," etc.

The interesting fact is that the numerical estimates, from the same eyewitnesses, bore essentially no statistical relationship to the subjective estimates. Six-footers were described as "short," by some witnesses; people a few inches over five feet in height were sometimes seen as "tall."

We were unable to establish proper statistical relationships here, because, frankly, there weren't any. Numerical and descriptive estimates of height were essentially unrelated. This fact, serendipitously noted in the context of more comprehensive experiments on other aspects of eyewitness processes, highlights a crucial forensic fact: witness estimates of suspect or perpetrator height may be extremely variable, and not necessarily accurate.

History provides many good examples of this phenomenon. Ferdinand Magellan, one of whose ships completed the first circumnavigation of the world, encountered "giants" in the Patagonian region of South America. These giants were reported to be simply enormous, so tall that some of the Spanish and Portuguese seamen were said to stand only waist-high to the Patagonians.

These estimates were not based on a paucity of experience; one of these giants sailed on with Magellan's expedition into the Pacific, ultimately dying of the rigors of this truly terrible trip. However, even with long-term exposure, estimates of perceived gargantuan stature persisted.

In fact, the Tehuelche people of Patagonia, of whom these "giants" were representative, did tend on average toward the relatively impressive height of six feet (Bergreen, 2003). Yet the Magellan expedition's estimates, running evidently to 8 or 9 feet tall, were obviously incorrect.

The true numerical estimates could not have matched those of subjective evaluation. This essentially provides Renaissance support for our more recent findings, in which modern people might perceive a person 6' tall to be "short" and a person 5'5" to be "tall."

This phenomenon is not confined to the realm of individual personal height; it may extend to dimensions in the inanimate world, as well. The first Spanish explorers to encounter the Grand Canyon in Arizona estimated the Canyon's width to be 7 to 12 miles, in the contemporary measurement of "leagues" (Hartmann, 2014). This was not bad; the average distance between the rims of the Grand Canyon is about 10 miles, ranging up to 18 miles depending on location.

However, when the explorers descended into the canyon, rock formations that appeared from the Canyon rim to be the "height of a man" turned out, on closer inspection, to be the height of "the biggest church tower in Seville" (Hartman, 2014, pg. 279). Quite a difference.

Human estimates of size and dimension are not necessarily wrong, as we see in the relatively accurate early estimates of the width of the Grand Canyon. However, other such estimates may prove to be spectacularly incorrect, as we see in the wildly variable early estimates of the height of Grand Canyon rock formations and in the "gigantic" height of the Tehuelche people encountered by Magellan.

Height and dimensional estimates are inconsistent and variable; sometimes right, sometimes wrong, but frequently not systematic. A wise detective or judge will not, therefore, put too much stock in this type of evidence.

The philosopher Protagoras suggested that "man is the measure of all things." This had a specific meaning within Sophist philosophy, not particularly applicable for us here. Yet even so, here we see this identical principle operating in a very specific way. As we examine what we see around us, we must make an attempt to ascertain the accuracy of the dimensions involved, and we try to do so; yet the perceived size of what we see, the height of a suspect in a criminal case or the size of a rock formation, may turn out not to be necessarily accurate, and may even depend upon whether we are asked for a numerical or a verbal estimate.

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These factors must be taken into account in any investigative or juridical proceeding. If not, we may assume computational accuracy on the part of a human nervous system which is frequently incapable of such accuracy, at least on a consistent and reliable basis. Our perceptions are highly variable across verbal or numerical estimates of size. This variability extends from human heights to the dimensions of inanimate objects.

All of this implies quite strongly that if a criminal case is highly dependent on subjective eyewitness estimates of size, in either the human or inanimate realms, that case rests on relatively flimsy and scientifically indefensible grounds. As we see from empirical research and from historical precedent, the human nervous system simply does not lend itself to highly accurate estimates of height or other dimensions.

What's more, numerical estimates may differ substantially from estimates expressed in more subjective terms. These facts may prove to be important in the consideration of criminal cases, now and in the future.

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