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Speed camera stats are like all Gov't - madf

As usual you cannot trust a word or a number issued by Gov't departments.. (quote from middle of report)

Dr Linda Mountain, an engineering academic from the University of Liverpool isn't convinced by these (road deaths and injuries) statistics. She has spent three years investigating an effect which blows a hole in the government's statistics on speed cameras. It's a statistical phenomenon known as "regression to mean".

In simple English, it refers to the fact that any extreme score - high or low - at one point in time will probably be less extreme the next time it's tested for purely statistical reasons. This is because scores always involve a little bit of randomness - which can go for or against you.

When applied to accident road safety, it's the idea that if nothing was done at an accident hotspot, the number of accidents might fall naturally anyway, with or without a speed camera. Basically, if you are at the top of a list of accident hotspots, there's only way to go and that's down.

Dr Mountain tried to factor this into the government statistics. Her figures were significantly different to the official ones. She found by including "regression to mean", the number of people killed or seriously injured at camera sites fell by just over 20%, half the government's estimate.

Her report was tucked away in an appendix in the last major evaluation, although the government does accept that "regression to mean" has a significant effect.


Speed camera stats are like all Gov't - Stuartli
New Labour is not going to let such small details spoil a perfect source of easy revenue is it?
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What\'s for you won\'t pass you by
Speed camera stats are like all Gov't - Leif
There are also suggestions that pressure is being applied to reclassify serious injuries as minor, so as to achieve targets.

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