What are the odds?

'The odds' are what is set by bookmakers. In real life, all you can say with certainty is that it is very unlikely. It is possible to predict certain events with some accuracy (like the WEATHER ;) ), but not really the movement of people.

He's asking for a probability, that's all. You've said nothing there but patronising nonsense. It is possible to come up with a reasonable probability based on simple assumptions about the movement of people.

For example the probability of chancing upon someone in a city is higher than not, as is the case for public transport.

I acknowledge that making the distinction between odds and probability is probably pernickety here (although they are different), but whether Jenne found it patronising is up to her. I hope not. It wasn't meant in this way.

Whether 'odds' or 'probability', if mathematically determined, both are models to impose on reality. I did say that it's possible to predict certain events with reasonable accuracy. However, this will be based on huge amounts of advance information, and most importantly, information that follows certain hierarchical rules and is easily quantifiable (and in itself in each component part relatively predictable). Horse-racing, for instance, is one such limited application where it works with a certain measure of reliability, and certain people can make a living from it by their knowledge of the odds and of the corresponding probability.

However, I defy you to ever create a reliable model of people prediction from which you would derive a probability or odds like that. As GS says, it would be hugely complex--far more complex than all the possible moves in a chess match, for instance. Who knows? Perhaps computers will one day be so powerful as to stretch to that kind of application (much as it would seem pointless and Big Brother-esquely worrying), but I maintain that it is currently not possible to calculate something like this--and she did ask for a method of calculation.

And I don't even think that this is possible for a single person, as in the example. It would be easier for certain people if the parameters are very limited, e.g. someone who lives like clockwork and never travels, but even they would be subject to conditions imposed by other people, making any predictive calculation too complex.

That may not satisfy you as the long version, but I certainly believe that it's true.