Safe Speed Forums

Tales of the unexpected - The Tale of Groundhog Island

Once upon a time there was a happy little Island called Groundhog Island. Every one was very happy – and things never ever changed.

It was such a happy Island that Noddy decided to live there with his lovely wife and children. Everything was perfect.

Then one day Noddy went to the local meeting hall and everybody was very very sad. Noddy asked what was wrong. The local bobby said “we are very happy but every year there were two deaths on the roads and as it was Groundhog Island no one could think of a way of reducing the carnage”. There were only two roads on Groundhog Island and the fatal accidents seemed to follow a relentless pattern. One year there were two accidents on Acacia Road and non on Halcyon Road. Next year there would be one accident on Acacia Road and one on Halcyon Road. And the year after there would be none on Acacia Road and two on Halcyon Road. Then the pattern would repeat. Now and again the happy islanders tried to think how to stop it – But being Groundhog islanders they never could and became very sad for a while.

Road........ Acacia Road Deaths... Halcyon Road Deaths
Year1.......................2..................... 0........................
Year2.......................1..................... 1........................
Year3.......................0..................... 2........................
Year4.......................2..................... 0........................
Year5.......................1..................... 1........................
Year6.......................0..................... 2........................ And so on……………………….

Noddy said what luck! “I used to run a camera safety partnership in my old country and by Jove do I know how to help you”.

Without further ado Noddy set to work using his old and trusted routine. Noddy did not know at the time that the Groundhog island spell had already had him in its grasp.

He immediately got hold of Year1 fatality data. He toiled day and night and his lovely wife and children missed him very much. Two days later Noddy ran naked down Acacia Avenue shouting Eureka.

Groundhog Island’s first speed camera was installed on Acacia Road as the last year it had had two fatal accidents. Noddy enjoyed life with his lovely wife and children.

Exactly one year later Noddy hurried to the police data computer and began analysing the safety camera partnerships effect From Year1 to Year2 Noddy was overjoyed as he had success in the palm of his hand.

He held a big get together in the meeting hall. This year it would be totally different. Noddy announced that according to the latest data the new speed camera had reduced fatalities by 50%. Everybody was very happy indeed – some politicians even had their photographs taken shaking Noddy’s hand. All the mathematicians agreed with Noddy that 2-1 divided by 2 = 50%.

Exactly one year later Noddy hurried to the police data computer and began analysing the safety camera partnerships effect for Year2 to Year3 Noddy was even more overjoyed he had more success in the palm of his hand.

He held a big get together in the meeting hall. This year it would be totally different. Noddy announced that according to the latest data the new speed camera had reduced fatalities by 100%. Everybody was very happy indeed. All the mathematicians agreed with Noddy that 2 was 100 % of 2.

This year there was a darker side. The accident rate on Halcyon Road was now at an all time high – according to the data Noddy had. Noddy said, “Hey – no problemo. I am the man to sort this out. The safety camera partnerships shoebox under Noddy’s bed is bulging with speeding fines – we will just stick another camera on Halcyon Road.” And so they did.

Exactly one year later Noddy hurried to the police data computer and began analysing the safety camera partnerships effect for Year 3 to Year 4. Noddy had to scratch his head a lot. It seemed that the First camera nicknamed “Old Faithful” had had two fatalities. Noddy was very puzzled indeed. He seemed to remember this problem in his old country – Noddy tried and tried but could find no solution.

Next morning Noddy ran naked down Acacia Avenue shouting Eureka. He ran to the phone box and phoned his old friend the public relations officer in the old safety camera partnership. “He said No problem Noddy. As a consultant, I sort this out for lots of safety camera partnerships. Present the data like this :-
Pre Camera fatality rate = 2 per year ( Year1 )
Post Camera fatality rate = 1+0+2 divided by 3 = 1 per year ( Year2 + Year3 + Year4 )

I can confidently state that old faithful is reducing fatalities by 50 %
Some bods mention regression to the mean – but I don’t see what that’s got to do with it”

Noddy thanked Dopey profusely, and now knew why PR men were paid so highly. The mathematicians all agreed with the sums.

The Halcyon Road Fatality rate was even better the year before the camera had two fatalities and the year after no fatalities. A whopping 100% reduction in fatalities.
Even the mathematicians would agree that the average result was 100 + 50 divided by two = 75%.

Noddy was even more overjoyed he had success through and through. He was so confident that he had broken the Groundhog Island spell that he went to see the wise old man on the hill and let him know.

Noddy went to the wise old man and told him all about “Old Faithful” and the latest speed camera. And that the Groundhog Island spell had been broken. The wise old man stared into Noddy’s eyes and said, – “It will take more than a safety camera partnership to do that” Noddy could not believe it - he was sure that the facts spoke for themselves, how could they possibly be wrong? The mathematicians all agreed as well. The wise old man said, “There is nothing wrong with the facts at all – you just have not told me about all of them.” Noddy could not believe it - the facts spoke for themselves. The wise old man said, “I was a Public relations officer for a camera safety partnership so I know how Dopey works.

If we look at the last 5 years the fatality rate has been 2,2,2,2,2 your cameras have done nothing !
Yet you claim 75% fatality reduction – and the mathematicians agree with your sums.

We wise old men call this Regression to the mean – You see Noddy your one mistake was concentrating on some of the facts and not the full picture. If you hadn’t we would have never found out.

And stop running down Acacia avenue naked your scaring my wife !

Now off with you back to Fairytale Island where people still believe in fairies and speed cameras.”

A very unexpected Tale

Noddy started to shake. This could not be possible. It took him a while to think the unthinkable. He tried to work out how many Safety camera partnerships allowed for regression to the mean in their published data. The fairy tale turned into a living nightmare. He realised the number was exactly ZERO.

HalcyonRichard April 14 2005

Excellent Richard. Thanks.

For details on 'Regression to the mean' (RTTM or RTM) in the real world see:

http://www.safespeed.org.uk/rttm.html
http://www.safespeed.org.uk/gambling.html
http://www.safespeed.org.uk/pr126.html
http://www.safespeed.org.uk/pr127.html

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Actually, I think Noddy is a bit too naive to be a scammer. What he should have done was:

Year 1: Acacia Road has 2 fatalities. Install Camera
Year 2: Acacia Road has 1 fatality. Claim 50% reduction
Year 3: Acacia Road has 0 fatalities. Claim 100% reduction

At this stage announce that the camera has done it's job, and can now be moved to Halcyon Road, where they seem to have a similar problem, with 2 fatalities this year.

Year 4: Acacia Road now has no camera, and a massive rise to 2 fatalities. Cite as conclusive proof that the camera was previously reducing fatalities. Plan to reinstate in Year 5 and look for a repetition of earlier results. Repeat process with Halcyon Road.

Each camera now shows a clear annual reduction of at least 50%, often more, and fatalities only ever rise when cameras are removed.

Noddy can now sit back, watch the money roll in, and spend his time trolling on internet forums under an assumed name...

_________________
CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!

Nice one Richard.

_________________
"CAMERAS "DO NOT" SAVE LIVES" !!
(Richard Brunstrom Says so !!)

Nice one Richard
PS - Does "Regression to the mean " in scamera speak mean regressing the speed limits downwards cos they're too mean to spend money on better solutions.

Brilliant!

now if you could just post it on a scamera pratnership forum (or Trainspot2000's), we can have some side bets on how long it will last before being deleted!

Hey, JT, are you sure that you are not really just a very clever forum incarnation of the "speedmaster general" ??? You sure understand how the partnerships do their statistical jiggery-pokery !

And Richard, that was excellent