*! version 1.1.5 30sep2009
help stci dialog:

Title

[ST] stci -- Confidence intervals for means and percentiles of survival time

Syntax

stci [if] [in] [, options]

Main
by(varlist) perform separate calculations for each group of
varlist

median calculate median survival times; the default

rmean calculate mean survival time restricted to longest follow-up time

emean calculate the mean survival time by exponentially extending the survival curve to zero

p(#) compute the # percentile of survival times

ccorr calculate the standard error for rmean using a continuity correction

noshow do not show st setting information

dd(#) set maximum number of decimal digits to report

level(#) set confidence level; default is level(95)

graph plot exponentially extended survivor function

tmax(#) set maximum analysis time of # to be plotted

Plot
cline_options affect rendition of the plotted lines

Add plots
"addplot(addplot_option:plot)" add other plots to the generated graph

Y axis, X axis, Titles, Legend, Overall
twoway_options any options other than by() documented in [G] twoway_options

You must stset your data before using stci; see
[ST] stset.

by is allowed; see [D] by.

Menu

Statistics > Survival analysis > Summary statistics, tests, and tables >
CIs for means and percentiles of survival time

Description

stci computes means and percentiles of survival time, standard
errors, and confidence intervals. For multiple-event data,
survival time is the time until a failure.

stci can be used with single- or multiple-record or single- or
multiple-failure st data.

Options

Main

by(varlist) specifies that separate calculations be made for each group
identified by equal values of the variables in varlist, resulting in
separate summaries and an overall total. varlist may contain any number
of variables, each of which may be string or numeric.

median specifies median survival times. This is the default.

rmean and emean specify mean survival times. If the
longest follow-up time is censored, emean (extended mean) computes the
mean survival by exponentially extending the survival curve to zero, and
rmean (restricted mean) computes the mean survival time restricted to
the longest follow-up time. If the longest follow-up time is a
failure, the restricted mean survival time and the extended mean survival time
are equal.

p(#) specifies the percentile of survival time to be computed. For
example p(25) will compute the 25th percentile of survival times, and
p(75) will compute the 75th percentile of survival times.
Specifying p(50) is the same as specifying the median option.

ccorr specifies that the standard error for the restricted mean
survival time be computed using a continuity correction. ccorr is
valid only with the rmean option.

noshow prevents stci from showing the key st variables. This
option is seldom used because most people type stset, show or
stset, noshow to set whether they want to see these variables mentioned
at the top of the output of every st command; see [ST] stset.

dd(#) specifies the maximum number of decimal digits to be reported for
standard errors and confidence intervals. This option affects only how values
are reported and not how they are calculated.

level(#) specifies the confidence level, as a percentage,
for confidence intervals. The default is level(95) or as set by
set level.

graph specifies that the exponentially extended survivor function
be plotted. This option is valid only when the emean option is also
specified and is not valid in conjunction with the by() option.

tmax(#) is for use with the graph option. It specifies the
maximum analysis time to be plotted.

Plot

cline_options affect the rendition of the plotted lines; see
[G] cline_options.

Add plots

addplot(plot) provides a way to add other plots to the
generated graph; see [G] addplot_option.

Y axis, X axis, Titles, Legend, Overall

twoway_options are any of the options documented in
[G] twoway_options, excluding by(). These include options for
titling the graph (see [G] title_options) and for saving the
graph to disk (see [G] saving_option).

Examples with single-record survival data

Setup

. webuse page2

Compute median survival time

. stci

Compute median survival time by group

. stci, by(group)

Compute the 25th percentile of survival time

. stci, p(25)

Compute the 25th percentile of survival time by group

. stci, p(25) by(group)

Compute mean survival time restricted to the longest follow-up time by
group

. stci, rmean by(group)

Compute mean survival time by exponentially extending the survival curve
to 0

. stci, emean

Same as above, but also plot the exponentially extended survivor
function

. stci, emean graph

Examples with multiple-record survival data

Setup

. webuse stan3

Compute median survival time

. stci

Compute median survival time by group

. stci, by(posttran)

Report whether values of posttran within subject vary over
time

. stvary posttran

Examples with multiple-failure data

Setup

. webuse mfail2

Show st settings

. stset

Compute median survival time

. stci

Create nf containing the cumulative number of failures for each
subject as of the entry time for the observation

. stgen nf = nfailures()

Compute median survival time by group

. stci, by(nf)

Saved results

stci saves the following in r():

Scalars

r(N_sub) number of subjects

r(p#) #th percentile

r(rmean) restricted mean

r(emean) extended mean

r(se) standard error

r(lb) lower bound of CI

r(ub) upper bound of CI

Also see

Manual: [ST] stci

Help: [ST] stdescribe,
[ST] stir, [ST] sts, [ST] stset, [ST] stvary,
[ST] stptime