program define survtab
version 2.1
	if "%_*"=="" {
		di in red "invalid syntax -- see help survcurv"
		exit 198
	}
	mac def _varlist "req ex"
	mac def _options "BY(string) AT(string)"
	mac def _if "opt"
	mac def _in "opt"
	parse "%_*"
	parse "%_varlist", parse(" ")
        if "%_at"=="" {
             di in red "Specify the time points for calculation of S"
             di in red "through inclusion of the at(t1[,t2[,t3..]]) option."
             di in yellow "Example: survtab surv fail,by(group) at(24,60)."
             di in yellow "         24 and 60 are the time points."
             exit
        }
	_crcsrv2 %_1 %_2 %_by %_in %_if
	mac def _rc = _rc
        capture drop _TIME
        capture drop _PRINT
        macro define _POINT " recode( %_1 , %_at , 9999) "
        quietly gen int _TIME = %_POINT
	quietly replace _atrisk=-_atrisk
        sort %_by _TIME %_1 _atrisk
        quietly by %_by _TIME : gen byte _PRINT=1 if _n==_N&_TIME~=9999
        quietly replace _atrisk=-_atrisk
        format _atrisk _TIME %_by %8.0f
        format _surv _stds   %8.3f
        noisily list %_by _TIME _atrisk _surv _stds if _PRINT==1
	exit %_rc
end