* !arpois.ado version 4.1.0 September 1998    STB-46 sts13
* Aurelio Tobias (IMIM) & Mike Campbell (University of Sheffield)
* Poisson regression allowing for autocorrelation and overdispersion
* (Schwartz et al. J Epidemiol Comminity Health 1996)

program define arpois
	version 5.0
	local weight "aweight fweight iweight pweight"
	local varlist "req ex min(2)"
	local if "opt"
	local in "opt"
        local options "ar(int 0) delete prev *"
        parse "`*'"
        parse "`varlist'", parse (" ")

	macro drop S_1

	if "`delete'"=="delete" {
		cap drop _rho*
		cap drop _z
	}

	if "`prev'"=="prev" {
		poisson `varlist' `if' `in'
	}
	else {
		qui poisson `varlist' `if' `in'
	}
	matrix XX=get(_b)
	local n=$S_E_mdf+1
	global N=$S_E_mdf+1
	local i=1
	while `i'<`n'	{
		global X`i'=XX[1,`i']
		local i=`i'+1
	}
	global X0=XX[1,`n']

	local i=2
	local j=1
	while `i'<=`n' {
		local v`j' : word `i' of `varlist' 
		local xvarl "`xvarl' `v`j''"
		global VX`j' "`v`j''"
		local i=`i'+1
		local j=`j'+1
	}

	tempvar eta  ey resid sigma 
	qui {
		local y="$S_E_depv"
		predict `eta'
		gen `ey'=exp(`eta')
		gen `resid'=(`y'-`ey')/`ey'
		gen _z=`eta'+`resid'
		gen `sigma'=1/sqrt(`ey')

		local i=1
		global nar=`ar'
		while `i'<=$nar {
			tempvar resid`i' sigma`i'
			gen `resid`i''=`resid'[_n-`i']
			gen `sigma`i''=`sigma'[_n-`i']
			gen _rho`i'=`resid`i''
			*gen _rho`i'=(`sigma'*`resid`i'')/`sigma`i''
			local arlist "`arlist' _rho`i'"
			global RX`i' "_rho`i'"
			local i=`i'+1
		}

		local i=1
		while `i'<=$nar {
		        global R`i'=0.001
			local i=`i'+1
		}
	}
	display in gre "log-linear autoregressive model " `ar' " order"
	display
	nl aphea _z `xvarl' `arlist' `if' `in' [aw=`ey']
end