st: Number of patients at risk from sts list - subgroup analyses

[James Morden <James.Morden@icr.ac.uk>]

Dear all,

I had a query relating to the number of patients at risk in survival analyses and wondered if anyone could help.

I am using the sts list command to calculate the number of events and patients at risk at different time points to go below a Kaplan-Meier plot. I also want to present graphs for a subgroup analysis, so separate K-M plots for two different groups. All patients are in one of these two groups. When using sts list to get the numbers at risk for each separate subgroup, I noticed that these do not add up to the overall figure, in fact always being 1 larger. Was there a reason for this, and anyway to get around it?
The number of events in each of the subgroups does seem to add up to the numbers in the overall analysis.

Many thanks,
James


James Morden
Medical Statistician
ICR Clinical Trials and Statistics Unit (ICR-CTSU) 
Section of Clinical Trials 
The Institute of Cancer Research 
Sir Richard Doll Building 
Cotswold Road 
Sutton, Surrey
SM2 5NG

Tel: 020 8722 4187


The Institute of Cancer Research: Royal Cancer Hospital, a charitable Company Limited by Guarantee, Registered in England under Company No. 534147 with its Registered Office at 123 Old Brompton Road, London SW7 3RP.

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