Cut of survival curve after number of risk drops below a certain number

[Stein Janssen]

Dear Forum members,

Is there a possibility in STATA to simply cut off survival curves (using the command sts graph) after the "number at risk" drops below a certain number?

For instance if I start with 1000 cases, I would like to stop the curve when the number at risk drops below 10. I can lookup at what time-point the number at risk drops below 10 and subsequently use the option [tmax(#)] to make a graph until that time-point is reached. However, this is not very practical and I can not use this when I have multiple survival curves in one graph.

Thanks in advance,

Stein Janssen

[Svend Juul]

You can use sts generate to calculate the survival function (s) and the number at risk (n). With the connect(J) option you will get a step curve.
You will need to define the origin of curves (0,1); below I show hos it can be done.

// Define origin of survival curves
clear
input drug _t s n
0 0 1 100
1 0 1 100
end
save origin.dta, replace

webuse drug2.dta, clear
sts generate s=s , by(drug)
sts generate n=n , by(drug)

append using origin.dta
twoway (line s _t if drug==0 & n>9, connect(J) sort) ///
       (line s _t if drug==1 & n>9, connect(J) sort)