from odds to probs

From: Doug (queanbeyan_at_hotmail.com)
Date: 01/17/05 

Date: 16 Jan 2005 22:30:15 -0800

Hi,

This simple enquiry is one that I haven't solved this morning and is
based on the odds ratio for logistic regression and the associated
probabilities.

The odds ration equation is O=P/(1-P) (odds=prob/1-prob) of event.
However in Paul Allison's logiistical regression book (page 11) he
also has P=O/1+O. While I know that this is true and is easily
checked with real data (eg 0.2=0.25/1+0.25) and (0.25=0.2/0.8), I
haven't done this type of maths for a while.

Could someone remind me of the maths steps in getting from O=P/1-P to
P=O/1+O.

It's monday - ok!

thanks

Doug

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