topic Re: Classification table proc logistic in SAS Procedures

Classification table proc logistic

Ektchup — Wed, 09 Dec 2015 15:45:55 GMT

Hi all,

I use PROC LOGISTIC to to find the most predictive combination of parameters(model) for diagnosis. The code is below:

%let list_param = AP01 AP02 AP03 AP04 AP05 AP06 AP07 AP08 AP09 AP10 AP11 AP12 AP13 AP14 AP15 AP16 AP17 AP18 AP19 AP20
AP21 AP22 AP23 AP24 AP25 AP26 AP27 AP28 AI01 AI02 AI03 AI04 AI05 AI06 AI07 AI08 AI09 AI10 AI11 AI12
AI13 AI14 AI15 AI16 AI17 AI18 AI19 AI20 AI21;

proc logistic data= Source plots(only)= roc;
class reasvis;
model acrstat = &list_param. age sexn reasvis/ CTABLE pprob=0.5 SELECTION=stepwise;
output out=probs6 PREDPROBS= i;
run;

acrstat - is dependent variable with values if the diagnosis is or no.

Predictors - list of parameters - &list_param, age, sex - all n umeric variables, reasvis - character variable.

And there are only 9 patients with diagnosis and 320 without it (Total number of subjects - 329) in Source dataset.

And I have some problems with it - actually procedure predicts that no diagnosis will occur. I think it is becouse of small amount of subjects with diagnosis.

But is it possible to find the model which will predict the occurance of diagnosis?

Thanks.

Re: Classification table proc logistic

ballardw — Wed, 09 Dec 2015 16:17:52 GMT

The large number of variables is perhaps a factor as well. When you look at the 9 diagnosis and all of the variables in the model to any 2 have the same factors? You don't indicate what your variables represent but if they are all of a "yes/no" or "Present/not present" it should be easy to check. If none of them have any in common then I wouldn't be surprised.

You could examine using Selection=Score see if any of the subsets do very well.

Re: Classification table proc logistic

Reeza — Wed, 09 Dec 2015 18:03:16 GMT

This is a logistic regression model with a small event rate. There are some known ways to deal with this, including assiging prior probabiliites via a Bayesian methodology.

http://stats.stackexchange.com/questions/10236/applying-logistic-regression-with-low-event-rate

You can find a better model by removing some variables that don't add value to the regression.

Re: Classification table proc logistic

Ektchup — Thu, 10 Dec 2015 07:41:49 GMT

HI, Reeza

Thanks.

The removing of parameters that are not statistically significant is performed by SELECTION=stepwise option. But despite on this I get the classification table without predicted diagnosis.

Re: Classification table proc logistic

Ektchup — Thu, 10 Dec 2015 07:52:48 GMT

Thanks, ballardw!

You don't indicate what your variables represent

The variables are numeric with 1 for 'Yes' and 0 for 'No'.

Also the removing of parameters that are not statistically significant is performed by SELECTION=stepwise.