topic Calculate the probability of a logistic regression in Statistical Procedures

Calculate the probability of a logistic regression

chowfar — Sun, 14 Aug 2016 20:40:27 GMT

Hi,

How can I calculate the probability of a logistic regression model given the values of independent variables not only by hand but also by SAS? Please show me some sample code.

Re: Calculate the probability of a logistic regression

Reeza — Sun, 14 Aug 2016 21:33:30 GMT

This is known as scoring a model.

As of SAS 9.4 there's the CODE statement that will generate the code you need to score your data.

See several of the options with example code here:

http://blogs.sas.com/content/iml/2014/02/19/scoring-a-regression-model-in-sas.html

This thread has a fully worked example that's a manual process BEFORE the availability of the CODE statement.

https://communities.sas.com/t5/SAS-Statistical-Procedures/How-to-determine-logistic-regression-formula-from-estimates/m-p/120780/highlight/true#M6321

I'd use the CODE option now.

Re: Calculate the probability of a logistic regression

PGStats — Mon, 15 Aug 2016 01:49:35 GMT

Note that the CODE generation is not implemented for all models. I learned the hard way (not in the doc) that I can't get the code for scoring a model containing a constructed spline effect. I am using version 13.1 but I don't see any mention of the feature being added to more recent versions.

Re: Calculate the probability of a logistic regression

Ksharp — Mon, 15 Aug 2016 02:12:31 GMT

There are about three way to score data: CODE , SCORE, STORE statements.
Check documentation example Example 72.16: Scoring Data Sets .

The simplest is SCORE

proc logistic data=Crops;
model Crop=x1-x4 / link=glogit;
score data=Test  out=Score1;
run;

Re: Calculate the probability of a logistic regression

chowfar — Mon, 15 Aug 2016 02:43:40 GMT

lets say I have the values for x1-x4, how can I find the logistic probability of Crop. What should be the code?

Re: Calculate the probability of a logistic regression

Reeza — Mon, 15 Aug 2016 02:52:43 GMT

@chowfar Have you looked at any of the indicated references? Which ones were unclear?

Re: Calculate the probability of a logistic regression

PGStats — Mon, 15 Aug 2016 03:11:38 GMT

Try @Ksharp's code. Start by omitting data=test to score the original data (the crops dataset).