.- help for orcalc .-Compute odds ratios -------------------

orcalc p1 p2 [p3 p4, refgroup(#)]

Description -----------

orcalc computes odds ratios based on the probabilities from a categorical predictor with 2, 3 or 4 levels. You supply the probabilities of Y=1 for each of the levels of the categorical predictor, and then the odds ratios are given.

By default, the last group is the reference group (sometimes called the omitted group). You can select the reference group via the refgroup option.

Example -------

If there are 2 leves for the categorical predictor, and the P(y=1) is .6 for the first group, and P(y=1) is .5 for the second group, you can get the odds ratio for group 1 vs. group 2 like this.

. orcalc .6 .5

If you wish to treat group 1 as the reference group from the above example, then use the refgroup option (abbreviated using ref) as shown below.

. orcalc .6 .5, ref(1)

Below we get the odds ratios for a 3 category predictor.

. orcalc .6 .5 .3

Authors -------

Philip B. Ender Michael Mitchell Statistical Computing and Consulting UCLA Academic Technology Services ender@ucla.edu mnm@ucla.edu