Re: Speed Cameras only save half lives claimed.

"OG" <owen@xxxxxxxxxxxxxxxxxxx> wrote in message news:6isf2sFaft4U1@xxxxxxxxxxxxxxxxxxxxx

"AndrewR" <andrew@xxxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:6isd8lFa1krU1@xxxxxxxxxxxxxxxxxxxxx
"OG" <owen@xxxxxxxxxxxxxxxxxxx> wrote in message news:6iscb2F9p61U1@xxxxxxxxxxxxxxxxxxxxx

But the number of accidents is merely a statistical value - it may represent a number of factors, but one of them is chance and chance is subject to regression to the mean.

But in the demonstration the only 'factor' is chance. So it is deliberately misleading to use it as a 'model' for accidents and cameras.


But the demonstration is not intended to model accidents and cameras - it is intended to explain, in a fashion understandable to journalists, what regression to the mean, er, means.

Nobody is seriously contending that the number of accidents in any given location is governed only by chance, but what is being suggested is that:

1. Chance is a hard element to eliminate from your measurement of how well a camera has performed.

2. Immediately after an unusually high number of accidents then the number of accidents is likely to drop irrespective of what you do, all other factors being equal.

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