Creating a survival curve when you have already calculated the percent survival at each time.

Prism can create Kaplan-Meier survival curves, and compare these with the logrank test (or the Wlcoxon-Gehan-Breslow test). To do this, enter data on a Prism table formatted as a survival table. You must enter one row of data per subject. 

But what if you already know the percent survival at each time point, and just want to make a graph? In this case, do not enter data onto a survival data table. That table requires information about each subject. Instead, create an XY data table. If you only want to enter percent survival, format the data table to enter single Y values  with no subcolumns. If you know the standard error of the survival at each time point (from calculations done elsewhere), then format the data table for entry of mean with SEM (in fact, the "mean" will be percent survival, and "SEM" will be SE of the survival percentage).

Enter time (as months or days or weeks) into X. You must enter this as a number, not a date. 

Enter percent (or fraction) survival into Y. Just enter the values (don't append percent symbols). 

Then polish your graph. If you want the graph to have a staircase look (which is traditional for survival curves), you can do that. This screen shot shows where to make this setting in the Format Graph dialog:

If you enter survival percentages on an XY table, it will not be possible to do any calculations. You won't be able to compute error bars or confidence bands, and wont' be able to compare survival curves under different treatments.