Those subjects are said to be censored. You know how long they survived so far, but don't know what will happen later. X is the # of days (or months…) they were followed. Y is the code for censored observations, usually zero.
Each subject must be entered on a separate row. Enter the same X value on two (or more) rows.
Different investigators handle this differently. Some treat a death as a death, no matter what the cause. Others treat death of an unrelated cause to be a censored observation. Ideally, this decision should be made in the study design. If the study design is ambiguous, you should decide how to handle these data before unblinding the study.
No. You can enter the rows of data in any order you want. It just matters that each Y value (code) be on the same row as the appropriate X value.
It doesn't. In either case, the observation is censored. You know the patient was alive and on the protocol for a certain period of time. After that you can't know (patient still alive), or can't use (patient stopped following the protocol) the information. Survival analysis calculations treat all censored subjects in the same way. Until the time of censoring, censored subjects contribute towards calculation of percent survival. After the time of censoring, they are essentially missing data.
No. Prism only can analyze survival data if you enter survival time for each subject. Prism cannot analyze data entered as a life table.
Yes. When you create a new survival table, you can choose to enter starting and ending dates, rather than number of days.
Most clinical studies follow the “intention to treat” rule. You analyze the data assuming the subject got the treatment they were assigned to receive, even if the treatment was never given. This decision, of course, should be made as part of the experimental design.
No. The time must exceed zero for all subjects. If you enter X=0, Prism simply ignores that row. More on survival curves with X=0.