Hello, Can I get help? I have the attached kind of material and I should create a time-dependant covariate from the variate "Optime"? I have tried using survsplit function but I don't know exactly how to do it. Or I can't get it to work. How can I split every id's follow-up time into two rows according the time of optime (The time they get treatment)? Best regards, Paula Iso-Markku -------------- next part -------------- A non-text attachment was scrubbed... Name: Time-dep.PNG Type: image/png Size: 17177 bytes Desc: not available URL: <https://stat.ethz.ch/pipermail/r-help/attachments/20141106/7ea76292/attachment.png>