1. We observed a variable name ‘LINKIDX’ in the medication dataset. It is defined as ‘ID FOR LINKAGE TO COND/OTH EVENT FILES.’ We are not sure how it links the files. It appears to be made by DUID + PID + X. What is ‘X?’
2. It has variables ‘RXCCC1X’, ‘RXCCC2X’, and ‘RXCCC2X’. They are defined as ‘MODIFIED CLINICAL CLASS CODE.’ Is it a modification of ICD9 codes in Hospital/Conditions dataset? If so, how are they modified? How are they related to each other as well as with ICD9 codes in Conditions and Hospital datasets?
3. Similarly, is there a relation between RXICD1X, RXICD2X, and RXICD3X, and ICD9 codes in other files? If they are related, what is the relationship? Are they related to RXCCC1X, RXCCC2X, and RXCCC2X too?
4. Which variable(s) will be removed from the testing dataset?