[R] no. at risk in survfit()

[Frank E Harrell Jr]

array chip wrote:
> Hi,
> 
> when I generated a survfit() object, I can get number
> of patients at risk at various time points by using
> summary():
> 
> fit<-survfit(Surv(time,status)~class,data=mtdata)
> summary(fit)
> 
>                     class=1
>  time n.risk n.event survival std.err lower 95% CI
> upper 95% CI 
>   9.9     78       1    0.987  0.0127  0.963     1
>  41.5     77       1    0.974  0.0179  0.940     1
>  54.0     76       1    0.962  0.0218  0.920     1
>  99.1     38       1    0.936  0.0328  0.874     1
> 
>                    class=2
>   time n.risk n.event survival std.err lower 95% CI
> upper 95% CI 
>    6.9    102       1    0.990 0.00976 0.971   1.000
>    8.0    101       1    0.980 0.01373 0.954   1.000
>   14.4    100       1    0.971 0.01673 0.938   1.000
>   16.1     99       1    0.961 0.01922 0.924   0.999
>   16.6     98       1    0.951 0.02138 0.910   0.994
>   18.7     97       1    0.941 0.02330 0.897   0.988
>    :
>    :
>    :
> 
> I have many censoring observations in the dataset, and
> I would like to know the number of patients at risk
> (n.risk in the above output) for certain time points,
> for example at 60, 72, etc, which is not available
> from the above printout for class=1. Is there anyway I
> can get them?
> 
> Thanks

The Design package's survplot function can print n.risk over equally 
spaced time points.  You might see an easy way to print this by looking 
at the code.  -Frank

-- 
Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University