Bookmark and Share

Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

st: RE: p-values for K-M point survival estimates using sts list

From   Allen Buxton <>
To   "''" <>
Subject   st: RE: p-values for K-M point survival estimates using sts list
Date   Wed, 25 Aug 2010 11:39:04 -0700

I have used a z-test for two samples with known mean and std deviation to match the output of a program called Epilog. This is to state that the KM estimate is the mean and the associated standard error are known. The confidence intervals are better.

Here is the form:

capture program drop epiwald
program define epiwald
version 9.2
args m1 s1 m2 s2
        local d = abs(`m2' - `m1')
        local s = sqrt(`s1'^2 + `s2'^2)
        local z = `d'/`s'
        local p = 2*(1-norm(`z'))
        local p1 = 1*(1-norm(`z'))
        foreach Xval in m1 s1 m2 s2 d s z p p1 {
                local txt = `"``Xval''"'
                local `Xval'=string(`txt',"%6.4f")
        di `"mu1=`m1', mu2=`m2', std1=`s1', std2=`s2'"'
        di `"difference=`d', std=`s'"'
        di `"z-value=`z'"'
        di `"p-value=`p'"'
        di `"p-1side=`p1'"'
        di `""'

. epiwald 0.5833   0.1423  0.1538   0.1001
mu1=0.5833, mu2=0.1538, std1=0.1423, std2=0.1001
difference=0.4295, std=0.1740

-Allen Buxton

-----Original Message-----
From: [] On Behalf Of Bell, Cynthia
Sent: Wednesday, August 25, 2010 8:42 AM
Subject: st: p-values for K-M point survival estimates using sts list

The "sts list" command provides point estimates, std errors, and confidence intervals at exact times during my observation period. I prefer confidence intervals to compare, say, 10-year survival estimates between groups but a journal requested p-values comparing group point estimates at specific time points. Is this possible in Stata? If not, it shouldn't be complicated to compute a p-value given a distribution for the K-M survival point estimate and the standard error, right?

Thanks very much,

Cynthia Bell
Division of Pediatric Nephrology and Hypertension
University of Texas-Houston, Medical School

*   For searches and help try:

*   For searches and help try:

© Copyright 1996–2017 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   Site index