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ldawg5962 · #4 July 7th, 2009, 05:22 AM

Quote:

Originally Posted by lep11

For your question about a beta value of 0.8 for age, it means that for each additional year of age, there is an increase in the odds ratio of exp(0.8).

So I've done some extra reading since I posted a reply this morning, and seem to have a better grasp of the basics of logistic regression.

Just to check: We have two sets, defined by an age difference of 1 (denoted $Age1$ and $Age2$ ). Suppose $X$ is a k-tuple of our independent variables, and $X_{Age1}$ and $X_{Age2}$ represent k-tuples that arise from a change of the independent variable Age from $Age1$ to $Age1 + 1 = Age2$ . Then the odds for $Age1$ is given by:

$a=\frac{P(X_{Age1})}{1-P(X_{Age1})}$

and for $Age2$ by:

$b=\frac{P(X_{Age2})}{1-P(X_{Age2})}$ .

The odds ratio is $\frac{a}{b}$ .

You are saying that if we increase Age2 again by one unit, and repeat the process to get an odds of c, then the odds ratio $\frac{a}{c}=\frac{a}{b}e^{0.8}$ .

Very sloppy I know, but let me know what you think.