How big was the Hindenburg? Players guess it five times too small

The Smithsonian calls it the longest aircraft of any type. It was longer than three Boeing 747s nose to tail, and only 24 metres shorter than the Titanic.

In 1910 Harry Hollingworth found that large stimuli get underestimated. This miss goes further. My first guess why was wrong.

Almost every player made the airship too short

On 24 September, the game asked players to size the Hindenburg next to a 4.5 metre Greenland shark.

Only 3 guesses were too big. 96 were at least five times too small. And this is not simple anchoring: every round starts at a wrong size, and the airship started at 73.5 metres. Anchors keep estimates biased toward the initial values, as Amos Tversky and Daniel Kahneman showed in 1974. Here three in four players moved away from it, downwards.

My first idea was the old photos, and the data said no

My hypothesis: we know the Hindenburg from old photos, high in the sky with nothing next to it. If that shrinks it, other old things should shrink too.

So I checked all 50 rounds of those ten days. The woolly mammoth came out 1.9 times too big, the Wright Flyer and the Ford Model T about right, the Airbus A380 spot on. It did not hold. Old or airborne is not enough.

The shark pulls guesses down, but not this far

The fair objection is the shark: picture it as huge, and everything next to it comes out small. The next day checks that. With the same shark as reference, players made Ulm Minster (161.5 metres) 2.5 times too small.

The Hindenburg came out another 2.2 times smaller than that. Hollingworth's pull explains part of the miss, not why the Hindenburg is the single biggest one in the data.

The only other airship shrank as well

On 19 September the Graf Zeppelin, 236.6 metres long, was the reference for Hoover Dam. Players made the dam 3.2 times too big, so the airship looked 3.2 times too small to them. Different day, same direction.

Out of 50 rounds, the two biggest misses were the two rounds with an airship in them.

My guess now: we picture the blimp

This is a guess. People hold a consistent assumed size for everyday objects, as Talia Konkle and Aude Oliva found in 2011. A 2015 review by Frederike Petzschner and colleagues explains the pull as a learned prior for each category, one that causes an underestimation of large magnitudes. And the only airships most of us have seen are probably blimps over a stadium.

That would explain the direction. A blimp fills the sky above a football ground, so it becomes our picture of a giant airship, and the Hindenburg gets squeezed down to it.

The typical guess of 46 metres is even smaller than a classic blimp, going by the lengths on Airships.net. So the blimp may explain the direction of the miss, not all of its depth.

What two airships can't tell us

The dam round could also mean players overrate dams. And these are 184 self-selected players on one day, not a representative sample. Still, almost all missed the same way. The Hindenburg returns on 14, 18 and 22 October; if it shrinks again, I will be more sure.

Picture four blimps

I would have guessed small too. Next time you picture an airship, check if it is a blimp. The Hindenburg was more than four of them. Estimates break with old prices too, and with where animals live.