R help - Mar 2011 - median survival time from survfit

Hello,

I am trying to compute the mdeian of the survival time from the function
survfit:
> fit <- survfit(Surv(time, status) ~ 1)
> fit
Call: survfit(formula = Surv(time, status) ~ 1)

records   n.max n.start  events  median 0.95LCL 0.95UCL
    111     111     111      20      NA      NA      NA

The results is NA? the fit$surv gives values between 1 and 0.749! Am I doing
this correct? Is there a correct way to do this?

Many thanks for your help,
Dunia

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On Mar 18, 2011, at 6:06 AM, Dunia Scheid wrote:
> Hello,
> 
> I am trying to compute the mdeian of the survival time from the function
> survfit:
> 
>> fit <- survfit(Surv(time, status) ~ 1)
>> fit
> Call: survfit(formula = Surv(time, status) ~ 1)
> 
> records   n.max n.start  events  median 0.95LCL 0.95UCL
>    111     111     111      20      NA      NA      NA
> 
> The results is NA? the fit$surv gives values between 1 and 0.749! Am I
doing
> this correct? Is there a correct way to do this?
> 
> Many thanks for your help,
> Dunia

Median survival is the time at which the survivorship function equals 0.5. Since
your minimum value appears to be 0.749, you never get there, thus the output
shows NA.

If you did not have any censored observations, median survival would also be the
point at which 50% of your sample has not yet observed the event of interest.

See ?print.survfit for additional information specific to this function.

HTH,

Marc Schwartz