* !rao.ado version 1.8, November 1997  STB-42 gr28
* Aurelio Tobias
 
program define grvar
    version 1.1
    local varlist "req ex min(2)"
    local if "opt"
    local in "opt"
    local options "`options' id(string) level(int 5) *"
    parse "`*'"
    parse "`varlist'", parse(" ")
    local SEi `1'
    local ni  `2'

    if "`id'"=="" {
       local id "O"
    } 
    else {
	local id "[`id']"
    }
    preserve
    if ("`if'"!="") {
       keep `if'
    } 
    if ("`in'"!="") {
       keep `in'
    } 

    tempvar i Ai Ci ti Vi SE tw1 s2 s3 SEt LDL UDL 
    local k=_N
    gen `i'=_n
    qui gen `Ai'=(9*`ni'-11)/(9*(`ni'-1)) 
    qui gen `Ci'=(18*(`ni'-1))/((9*`ni'-11)^2) 
    qui gen `Vi'=`SEi'^2 
    qui gen `ti'=(`SEi'^(2/3))/`Ai' 
    qui summ `ni' 
    local N=_result(18) 
    qui gen `tw1'=`ni'*`ti' 
    qui summ `tw1' 
    local tw2=_result(18) 
    local tw=(1/`N')*`tw2'
    local s1=`tw'/`N'
    qui gen `s2'=`N'*(`N'-2*`ni')*`Ci' 
    qui gen `s3'=(`ni'^2)*`Ci' 
    qui summ `s3' 
    local s4=_result(18) 
    qui gen `SEt'=`s1'*((`s2'+`s4')^(1/2)) 
    local z=(-1)*invnorm((`level'/100)/(2*`k'))
    qui gen `LDL'=`tw'-`z'*`SEt' 
    qui gen `UDL'=`tw'+`z'*`SEt' 

    local j=2
    local xlist="1"
    while (`j'<=`k') {
       local xlist "`xlist',`j'"
       local j=`j'+1
    }
    graph `LDL' `ti' `UDL' `i' , c(l.l) sy(o`id'o) pen(212) yline(`tw') /*
    */ t2(" ") b2("Sample number") xlab(`xlist') `options' 

end