*! STB-6: smv5
*! version 2.0
/*  Modified from Poisson.ado by:
   D. H. Judson
   Department of Sociology
   Washington State University
   Pullman, WA 99164-4020
   (509) 335-4595
   Program code enhancements and suggestions are welcome at the above address.
   This program calls ado files:
         emdef.ado
         _crclf.ado
   STATA version: 2.1, 12/1/91 */
program define poilog
	version 2.1
         mac def _options "Ltol(string) Iter(string) Offset(string) Rescale *"
         mac def _varlist "req ex"
         mac def _in "opt"
         mac def _if "opt"
         mac def _exp "opt"
         parse "%_*"
         parse "%_varlist", parse(" ")
         mac def _dv "%_1"
         cap assert %_1>=0 & %_1==int(%_1) %_if %_in
         if (_rc>0) {
                 di in bl "Note:  You are responsible for interpretation of non-count dependent variable"
         }
         mac shift
         qui gen _wt = 1
         if ("%_exp"!="") {
                 qui replace _wt %_exp
         }
         if ("%_rescale"!="") {
                 di in bl "Note:  You are responsible for interpretation of rescaled weights"
                 qui summ _wt %_if %_in
                 replace _wt = _wt / (_result(3))
         }
         if ("%_ltol"=="") {
                 mac def _ltol "1e-7"
         }
         if ("%_iter"=="") {
                 mac def _iter 100
         }
         if ("%_offset"!="") {
                 mac def _poffset "+%_offset"
                 mac def _moffset "-%_offset"
                 mac def _offopt "offset(%_offset)"
         }
         mac def _dll = 1
         mac def _niter 0
         capture {
                 gen long _lastobs=_n %_if %_in
                 replace _lastobs=. if %_dv==. | _wt==.
                 replace _lastobs=_lastobs[_n-1] if _lastobs==.
                 mac def _lastobs=_lastobs[_N]
                 drop _lastobs
                 summ %_dv %_exp %_if %_in
                 mac def _emu = _result(3)
                 if ("%_offset"!="") {
                         gen float _predz = exp(%_offset)
                         summ _predz %_exp %_if %_in
                         mac def _emu = %_emu / _result(3)
                         drop _predz
                 }
                 gen float _predz = log(%_emu) %_poffset %_if %_in
                 gen float _epred = exp(_predz) %_if %_in
                 mac def _nobs=_result(1)
                 _crclf _Poisson = %_dv %_if %_in
                 replace _Poisson = sum(_Poisson*_wt) %_if %_in
                 mac def _llconst = _Poisson[%_lastobs]
                 replace _Poisson = cond(%_dv==0,0,%_dv*(log(%_dv)-1)) %_if %_in
                 replace _Poisson = sum(_Poisson*_wt) %_if %_in
                 mac def _llperf = _Poisson[%_lastobs] - %_llconst
                 replace _Poisson= %_dv*_predz - _epred %_if %_in
                 replace _Poisson= sum(_Poisson*_wt) %_if %_in
                 mac def _ll0 = _Poisson[%_lastobs] - %_llconst
                 mac def _myll = %_ll0
                 di
                 while ((abs(%_dll)>%_ltol*abs(%_myll) & %_niter<%_iter) | (%_niter==0)) {
                         di in gr "Iteration %_niter: Log Likelihood = ", /*
                         */ in ye %_myll, in gr "Change = ", in ye %_dll
                                  /* CHANGED ABOVE LINE: ADDED CHANGE =... */
                         replace _Poisson = ((%_dv - _epred)/_epred) + _predz %_moffset %_if %_in
                         reg _Poisson %_* =(_epred)*_wt, noscale
                         mac def _regF = _result(6)
                         mac def _regMDF = _result(3)
                         mac def _RMSE = _result(9)
                         drop _predz
                         predict _predz %_if %_in
                         replace _predz = _predz %_poffset
                         replace _epred = exp(_predz)
                         replace _Poisson = %_dv*_predz - _epred %_if %_in
                         replace _Poisson = sum(_Poisson*_wt) %_if %_in
                         mac def _mynll = _Poisson[%_lastobs] - %_llconst
                         mac def _dll = %_mynll - %_myll
                         mac def _myll "%_mynll"
                         mac def _niter = %_niter+1
                 }
                 * In the future:
                 * replace _Poisson = (%_dv - _epred)
                 * cap noisily _huber _Poisson _epred %_exp %_if %_in
                 replace _Poisson = ((%_dv - _epred)/_epred) + _predz %_moffset

                                  /* CHANGED ABOVE LINE. REMOVED /%_RMSE */

		 if ((abs(%_dll)>%_ltol*abs(%_myll)) | %_niter>=%_iter) {
			di in bl "ERROR: Convergence not achieved. Estimates should be considered"
			di in bl "highly suspect or in error. Last change = ", in ye %12.11g %_dll
		 }
		 else di in bl "Note: Convergence achieved. Last change = ", in ye  %12.11g %_dll

				/* CHANGED SEVERAL LINES ABOVE. ADDED INFO.
				   ON CONVERGENCE CRITERION. */

		 di
                 di in gre "Poisson Regression (Log link function)" _col(49) /*
                      */   "Number of cells =" in yel %8.0f %_nobs
                 di in gre "Goodness of fit chi2(" %_nobs-%_regMDF-1 ") =" /*
                      */ in yel %10.3f -2*(%_myll - %_llperf) /*
                      */ _col(49) in gre "Model chi2(%_regMDF) =" /*
                      */ in yel %8.3f 2*(%_myll-%_ll0)
                 mac def S_RSLT2 = 2*(%_myll-%_ll0)
                 mac def S_RSLT3 = %_regMDF
                 di in gre "Prob > chi2              = " /*
                     */ in yel %9.4f chiprob(%_nobs-%_regMDF-1,-2*(%_myll-%_llperf)) /*
                     */ _col(49) in gre "Prob > chi2   =" /*
                     */ in yel %8.4f chiprob(%_regMDF,2*(%_myll-%_ll0))

		/* CHANGED ABOVE LINE: REPLACED %regMDF with %_regMDF */

                 di in gre "Log Likelihood           =" in yel %10.3f %_myll
                 qui reg _Poisson %_* =(_epred)*_wt, noscale
                 mac def _RMSE = _result(9)

                         /* CHANGED ABOVE LINE, ADDED MAC DEF */

                 di
                 di in gre "Variable |  Coefficient    Std. Error       t    Prob > |t|        Mean"
                 di in gre "---------+" _dup(62) "-"
                 mac def _x = 8-length("%_dv")
                 di _dup(%_x) " " in gre "%_dv |", /*
                   */ in yel _col(61) %10.0g %_emu
                 di in gre "---------+" _dup(62) "-"
                 parse "%_* _cons", parse(" ")
                 while ("%_1"!="") {
                         emdef S_t : t %_1
                         mac def S_t=%S_t*%_RMSE

                                  /* CHANGED ABOVE LINE ADDED *%_RMSE */

                         if ("%_1"!="_cons") {
                                  cap summ %_1 %_exp %_if %_in
                                  mac def _mm = _result(3)
                         }
                         else {
                                  mac def _mm 1
                         }
                         mac def _x = 8-length("%_1")
                         di _dup(%_x) " " in gre "%_1 |", /*
                         */ in yel _col(15) %8.0g _b[%_1], /*
                         */ _col(28) %8.0g abs(_b[%_1]/%S_t), /*
                         */ _col(37) %8.3f %S_t, /*
                         */ _col(46) %8.3f tprob(%_nobs-%_regMDD-1,%S_t),/*
                         */ _col(57) %10.0g %_mm
                         mac shift
                 }
                 di in gre "---------+" _dup(62) "-"
                 mac def S_RSLT1 = %_nobs
         }
         mac def _rc = _rc
         cap drop _Poisson
         cap drop _predz
         cap drop _epred
         cap drop _wt
         exit %_rc
end