htasurv is a Stata module for assessing alternative parametric distributions when extrapolating survival data for use in health economic models. The function distfind loops through alternative distributions (specified by the user) and reports statistics and produces plots specified in NICE DSU TSD 14.0. The function distanalysis writes out results and useful statistics (e.g. variance-covariance matrix) for the analyst. The module can be installed directly from github, using the github module. Once the github module is installed, installation of htasurv is:
github install sourceHEOR/htasurv
For distfind:
distfind [varlist] [if], dlist(string) timevar(varname) failure(varname) [GRaphs] [SUPpress]
Where varlist are the variables in the survival model (often treatment), timevar is the variable defining the time-to-event, and failure is a binary variable for failure vs censoring (1=failure, 0=censored). If the graphs option is used, plots will be saved to curentdirectory/graphs.dlist is the list of distributions to estimate as lowercase strings (see example below). If the suppress option is used, the Cox-Snell residuals will not be plotted. The resulting table of diagnostics is returned in e(diags).
For distoutput:
distoutput [varlist] [if], dlist(string) fname(string) sname(string)
distoutput will estimate the models with variables given in varlist with distributions given in dlist (full title; all lowercase). The resulting models will be written to fname on sheet sname along with standard errors, 95% confidence intervals, and variance-covariance matrices.
sysuse cancer.dta, clear
global dlist "gamma ggamma weibull gompertz exponential lognormal loglogistic"
distfind age i.drug, dlist($dlist) timevar(studytime) failure(died)
matrix a = e(diags)
matrix list a
distoutput age i.drug, dlist($dlist) fname("test.xls") sname("outcome")
distplot if drug==1, exrange(60) intrange(10) dlist($dlist) drugnames("Placebo Drug2") ytitle("Proportion alive") xtitle("Time (Months)")
distplot if drug==2, exrange(60) intrange(10) dlist($dlist) drugnames("Placebo Drug2") ytitle("Proportion alive") xtitle("Time (Months)")
distplot if drug==3, exrange(60) intrange(10) dlist($dlist) drugnames("Placebo Drug2") ytitle("Proportion alive") xtitle("Time (Months)")
recode drug (1=0) (2=1)
distplot drug if drug==0 | drug==1, exrange(60) intrange(10) dlist($dlist) drugnames("Placebo Drug2") ytitle("Proportion alive") xtitle("Time (Months)")
D Trueman
Source Health Economics