After analysing 10 years’ worth of data on suicides at 71 Japanese train stations, Ueda and her colleagues found that there was some evidence of an effect on passengers. They saw an 84% reduction, a figure that was soon widely reported.

Unfortunately, that’s not the whole story. When news reports about the findings came out, Masao Ichikawa at the University of Tsukuba took another look at the data. He pointed out that it was important to distinguish between data collected during the day and night at outdoor train stations. During the day, the lights may be easily missed, or even turned off.

Ichikawa also scrutinised a measure known as the “confidence interval”. Statistical analyses always carry an inherent uncertainty around a particular result – such as the size of this effect – and the confidence interval expresses the possible range of those values. Ichikawa noticed that the confidence in in Ueda’s paper was extremely wide: 14-97%. “Statistically very unstable,” he says. This means the actual effect could have been as low as a 14% reduction – still a significant change, but not nearly as big as the media coverage had suggested.

He hoped his own paper, published in response the following year, would ensure that people didn’t begin thinking that blue lights were a miracle deterrent – that they somehow had an extraordinary effect on people who were considering suicide.

The installation of protective barriers and screen doors along the edges of platforms could be far more useful, says Ichikawa. However, he acknowledges that they cost a lot more than blue lights. The expense may be worth it, though, if the blue light effect turns out to be minimal.

Since publishing her paper, Ueda has been stunned by the number of enquiries she gets from railway firms around the world, including Switzerland, Belgium and the UK. “It’s amazing,” she says. There are already at least two examples of blue light installations in Britain – one at a train crossing in Scotland, and there are also such lights at Gatwick airport train station.