Re: collective intelligence - bayes theorem help

[yegg <gabriel.weinberg@gmail.com>]

> So there would be a 50% chance that Jonathan follows Toby given that he's
> from NJ.  So from what I understand, in order to find the probability that
> Jonathan follows Toby given that he's in Philly Lambda, and he's from NJ I
> would multiple the probabilities of each together.
>
> 1 * .5 = 50%
>
> So I think that I could say that there's a 50% chance that a person from NJ
> and in Philly Lambda follows Toby.  Is that correct given this simplistic
> approach, or am I doing something wrong?

This assumes the attributes are completely independent of each other.
Take the case of language attributes, e.g. who uses Perl and Lisp.
Suppose both were 50% (of the people who follow Toby).  By this logic,
the final probability would be 25%.  But what if the exact same people
who use Lisp also use Perl, then the real answer would be 50% because
the additional attribute tells you nothing.  It would only be 25% if
they were completely independent.


>
> I don't know anything about the other stuff you mentioned (Bayes classifier,
> regression analysis) so I'll have to try and read a bit about them and see
> how I may be able to use them.  

You can do this in Excel.  The help is helpful.  Basic linear
regression is built in.  To do more advanced stuff, do Tools->Add Ins,
add Analysis and Solver.  Then you can do Tools->Data Analysis.