Does placing a fly on a urinal improve cleanliness in men's toilets?

Question

Recently Richard Thaler won the Nobel Prize for Economics for his "Nudge" Theory.

Pretty much every news agency (in the UK at least) has chosen to explain his theory by using the "Fly on a Urinal" that was implemented at Amsterdam Airport and then promptly copied/sold all over the world.

In probably the most well-known example, spillage around the toilet, an age old problem for at least half of the human race, was cut by 80% using an ingeniously simple intervention.

I can find literally no Evidence that the "Fly on the Urinal" thing actually works though. I can find studies on the right place to aim and this is presumably where they place the "Fly". But nothing seems to suggest that doing this actually makes people aim here or that it improves overall cleanliness of toilets. The 80% value seems to have no backing at all that I can find. Given that Nudge theory is aimed at economics I'm not even convinced that this is a valid attribution of Richard Thaler's work.

The best I could find was from this article:

It is difficult to know for certain how much having a urinal target reduces cleaning needs. Some purveyors of this idea claim that it can reduce spillage by up to 80%, but Reichardt is sceptical. ‘As I have learnt over the past 25 years, bathroom behaviour can be really strange. Perhaps 60–70% might start to pee towards the fly; the others probably wouldn’t care so much. I’d say the reduction in spillage is probably more like 50%, but even so, that is still noticeable.’

This is actually interestingly misquoted in the Washington post

Kieboom reported an astonishing 80 percent reduction in urinal spillage after introducing the flies

See actual quote below:

Schiphol is often cited as the source of studies done into spillage reduction, but it appears that no such studies have taken place. Kieboom says that he was certainly never aware of any scientific research done into the effects of the fly, and that the 80% figure was ‘very empirical’.

So is there any evidence that placing a fly on a urinal actually improves cleanliness in men's toilets? Or is this (as I guess) a clever marketing gimmick gone viral? Where did the 80% claim come from? It seems very prevalent and is reported as fact everywhere that I can find, apart from the web site with the direct quote from "Kieboom" above.

Answer 1

Where did the 80% claim come from?

According to the 2009 NPR article There's A Fly In My Urinal:

When flies were introduced at Schiphol Airport, spillage rates dropped 80 percent, says manager Aad Keiboom

See also the 13 May 1997 Santa Cruz Sentinel:

Just visit the men's room. The tile under the urinals in the Arrivals Building has that familiar lemony tinge; rubber soles stick to it. Over in Amsterdam, the tile under Schiphol's urinals would pass inspection in an operating room. But nobody notices. What everybody does notice is that each urinal has a fly in it. Look harder, and the fly turns into the black outline of a fly, etched into the porcelain. "It improves the aim," says Aad Kieboom. "If a man sees a fly, he aims at it." Kieboom, an economist, directs Schiphol's own building expansion. His staff conducted fly-in-urinal trials and found that etchings reduce spillage by 80 percent.