Frank: This data is from a cancer registry, so I'm not so concered about the issues you've mentioned. I would be if this was actual hospital data and then everything you said is of concern.

David: You're right about the non-cancer patients, I hadn't thought of the information that could be lost. However, I think there is some confusion on the cancer patients. I am trying to predict time to first cancer diagnosis (ie. I don't care what other dx's they have, even if ithey have multiple cancers, I want to only the first cancer).

In a nutshell, I have duplicate records due to multiple ICD code diagnoses and I want only one record per subject. If they have cancer (or more than one cancer), I want the record with the first cancer diagnosis age, if they do not, I still want one record, maybe I can use the latest age available so I don't lose any data as David suggests.

Thanks for the continued discussion.

Neerav