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I am trying to figure out how to properly create a survival curve for brain tumour patients. I was referring to this paper (https://statsdirect.com/help/survival_analysis/kaplan.htm) to educate my self. I don't get the same values for the probability as you do. This is probably trivial, but it would help me a lot if you could help me understand they why :)

I used the values for the Group: 1 (Group Surv = 2) in the first able as shown below.

require 'sstat'
sstat_survival = SStat::Surv.new

time =     [142, 157, 163, 198, 204, 205, 232, 232, 232, 233, 233, 233, 233, 239, 240, 261, 280, 280, 295, 295, 323, 344]
censored = [0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1]
sstat_survival.kaplan_meier(time, censored)
sstat_survival.kaplan_meier_3p_extraploation(time, censored)

Thank you!