Sunday, 6 February 2005

Colley's Rule: making decisions

What's the best way to choose the most suitable Christmas gift, or the most fun party to go to, etc etc?

In December I saw a lighthearted article by Robert Matthews in the Financial Times, in the pre-Christmas context, suggesting the application of scientific rules to some Christmas-related problems. One which particularly struck me was Collee's Rule (also known it seems as Colley's Rule), apparently named after a British doctor who popularised it in the 1990's, although the rule seems to date back from before that.

The article said that the rule had recently been mathematically proven - and it seems to me a brilliantly simple yet fantastically useful rule one could apply in practice.

Here's how it works:

* Find yourself something which looks suitable
* Then put it back or reject it!
* Keep looking
* Take the first thing you find that's better than the one you put back or rejected.

It seems that, scientifically speaking, following this rule makes it much more likely that you'll end up making the best choice, compared with taking the first thing that comes along.

But note that the rule only works to produce the best outcome for decisions in situations where there is no going back (e.g. because you've no time to retrace your steps, like when you're on a one-day shopping trip, or it's something like a job offer where you can't exactly go back and take the one you rejected before!). The article applied the rule somewhat tongue in cheek (and obviously against the principles behind the rule) to party invites too, suggesting that if you didn't get a better offer than the first invite that you'd already rejected, you could always go gatecrash it!

Oddly enough I could find very little on the Net about Collee's Rule - just this blog mention and this newsgroup thread (which I must say I found a bit of a struggle to comprehend, maths eeeek!). [Added 9 June 2005:] See also this interesting article from

If anyone decides to try Collee's Rule and would like to share their experiences about their use of Colley's Rule in real life, and whether it actually worked for them, I'd be really interested to hear all about it.
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