To prove that speed cameras reduce accidents, the authorities frequently point to the number of road accident fatalities in London after the introduction of speed cameras. They state that fatal accidents in London fell from 276 in 1997 to just 226 in 1998, a reduction of 18%, and go on to claim (without any evidence whatsoever) that this reduction was entirely due to speed cameras.

Fatal Road Accidents in London 1997-1998
  276
226
 
  1997 1998  

So that's clear then isn't it? Speed cameras reduce accidents.
All very convincing if you only bother to look at the data they present to you, and listen to the explanation they attach to it.

But hang on a minute, why do they only show data from 2 years? Lets look at the bigger picture:

Fatal Road Accidents in London 1994-1999
  270
214
251
276
226
264
 
  1994 1995 1996 1997 1998 1999  

Well isn't that a co-incidence? The year they chose to install speed cameras was a particularly bad year for accidents. The following year, surprise surprise, accidents were lower; though not as low as in 1995 when there were no speed cameras, something they fail to mention.

And why did fatal accidents increase again in 1999 when the speed cameras were still in place?

The truth is that accidents occur at random for many reasons, they do not occur at regular intervals, therefore in any given year there will be a random number of accidents, and it is simply not possible to conclude that any minor variation either way is due to anything other than random fluctuation.

To take two years in isolation and attempt to claim a relationship between a random fluctuation in accidents and the use of speed cameras is statistical chicanery at best, and at worst a downright lie.

This is yet another example of how the government simply cannot be trusted when it comes to pronouncements about 'speed'. They are only interested in using propaganda to brainwash the public into accepting more speed cameras, so as to extort yet more stealth taxes in the form of fines.

We have only to wonder what the authorities attribute the greater reduction from 270 fatalities in 1994 to 214 in 1995 to — the Spice Girls perhaps?