*! version 1.0.0 24oct2007
help survci

Title

survci -- Pointwise confidence bands for the covariate-adjusted survivor function after stcox

Syntax

survci [if] [in] [, options]

Main
basesurv(varname) use baseline survivor function varname

at(# # ...) values of the specified
covariates; default is means of the covariates

cltype(loglog|log|normal) type of the transformation for the
confidence bands; default is loglog

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

outfile(filename[, replace]) save the
plot data to filename; use replace to overwrite existing
filename

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

Description

survci plots pointwise confidence bands for the covariate-adjusted
survivor function after stcox. Estimates of the survivor function,
standard errors, and lower and upper bounds may be optionally saved.

Options

Main

basesurv(varname) specifies the name of the variable containing the
estimates of the baseline survivor function. By default, it uses the variable
in e(bases) saved by stcox.

at(# # ...) specifies the values of the covariates used in stcox
for which the estimates of the survivor function are to be computed. The
number of values should be the same as the number of covariates specified with
stcox. By default, means of the continuous covariates and 0 for the
binary covariates are used.

cltype(loglog|log|normal) specifies the transformation of the confidence
intervals to be used in the computation. The default is loglog. This
interval is of the form [S^exp(z*se/S/ln(S)), S^exp(-z*se/S/ln(S))] where S is
the estimated survivor function, se is the standard error of S, and z is the
normal-based critical value. If log is specified the confidence
interval [S*exp(-z*se/S), S*exp(z*se/S)] is computed. If normal is
specified the confidence interval [S-z*se, S+z*se] is computed.

level(#) specifies the confidence level, as a percentage, for the
pointwise confidence interval of the survivor function; see [R] level.

outfile(filename[, replace]) creates a Stata data
file (.dta file) containing the values used to produce a graph.
replace indicates that filename be overwritten, if it exists.

Y axis, X axis, Titles, Legend, Overall

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

Remarks

The formula for the asymptotic variance of the covariate-adjusted survivor
function is given in Marubini and Valsecchi (1995, 221), among others, and is
based on the asymptotic variance of the cumulative hazard function derived by
Tsiatis (1981). The pointwise confidence intervals are computed using one of
the three transformations as described above in the description of
cltype(). The estimates are not available with survey or
multiple-record survival data.

Examples

Plot pointwise confidence bands for the survivor function adjusted for
age=60 using the product-limit estimate of the baseline survivor
function.

. sysuse cancer
. stset studytime, failure(died)
. stcox age, basesurv(s0)
. survci, at(60)

Plot pointwise confidence bands for the survivor function adjusted for
age=60 using the estimate of the baseline survivor
function based on the cumulative hazard.

. stcox age, basech(h0)
. gen double s0_ch = exp(-h0)
. survci, at(60) basesurv(s0_ch)

Request log-based confidence intervals in the above.

. survci, at(60) basesurv(s0_ch) cltype(log)

References

Marubini, E., and M. G. Valsecchi. 1995.
Analysing Survival Data from Clinical Trials and Observational Studies,
UK: Wiley.

Tsiatis, A. A. 1981.
A large sample study of the estimate for the integrated hazard function in
Cox's regression model for survival data.
Annals of Statistics 9: 93-108.

Also see

Online: [ST] stcurve, [ST] stcox, [ST] stset