I am planning on doing a Cox model analysis to study risk factors for a disease, retrospectively via medical record review. Will the model allow for mixing of binary , continuous, and/or ordinal variables in one equation? I am using Redcap, which allows you to create a data-form with a graphical user interface with multiple choice questions, text fields where you can input an integer, calendar drop-downs for dates, etc etc...and in the end you can export an Excel sheet of the raw data with which to perform the analysis. My question is simply what is the best way to encode these questions on the data form to make the raw data more amenable to cox modeling? For example, if one of our covariates is number of previous cancers, would it be best to set this up as a textbox where you type in the integer or as a multiple choice question that has "1" through "10+" as options? (We decided that we don't want to bother counting after 10 so we will encode everyone with more than 10 prior cancers as simply "10+")
Another issue is the variable of treatment modality. Currently we have this set up as multiple choice "check-boxes", i.e. the ones that allow you to select more than one option. This way we could select all the adjuvants that people had on a case by case basis. However, I am starting to worry that this will present an issue for the cox analysis...Would it have been better to think of all the different possible combinations of therapies and make each of them one of the multiple choice options? i.e. instead of having it as : surgery [X], chemo [X], radiation [X] ....we could have it as surgery, chemo, and radiation [X]....The automatically generated excel sheet that I mentioned will convert everything into a binary variable (unless of course you manually input integers for continuous variables).