How do you create interaction terms in a conditional logistic regression model?

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David Eugene Booth

COXREG is for proportional hazards models with censored DV, unless I misunderstand something. You might take a look at the link below. Best, David

http://core.ecu.edu/psyc/wuenschk/MV/multReg/Logistic-SPSS.pdf

Yolanda J. McDonald

Hello David,

I appreciate your response and link.

I should have noted that my research design is a case-control study, individual matched 1 case to 3 controls. I used COXREG because it is a work around for conditional logistic regression based on these sources:

http://www-01.ibm.com/support/docview.wss?uid=swg21477360

https://www.youtube.com/watch?v=be-M0tMMKyU

SPSS worked until I tried interaction terms.

I could try R but based on the blogs and message boards (no answer to the problem) interaction terms in conditional logistic regression in R are problematic. I tried SPSS first since I am more familiar with it and thought it would be more efficient to troubleshot in SPSS.

Yolanda, Thanks I didn't know all of this about SPSS. Be careful in two places. First some packages when you write x1*X2 create all combinations. Thus you might end up with a full factorial model which has 0 df if you don't replicate. this may be your problem with the coeffs. Second problem might come up because COXREG is looking for Censoring information. have you taken care of that? I doubt this helps much but here it is, Best, David

I do not have censoring information because all of the cases and controls are from two different registries that were matched on age and year of diagnosis (reference date) -- no participants dropped from the study or were added at a later date. However, I am wondering if SPSS is looking for this since I am using COXREG.

As for the full factorial model and replication. I need to look into it that since I am not familiar with how it works.

Thanks again. I appreciate your help.

I realized I did have censoring in the SPSS output, i.e. my controls. I finally decided to use R, which worked nicely for conditional logistic regression. Also, this video is good resource for how to create an interaction term in R.

https://www.youtube.com/watch?v=RWzpGudsnxA