*! version 1.0.0 20 January 1994  RG            sg43: STB-28
program define modt
    version 3.1
* if var1=var2 then var1 should be control group
* if using "by()", then lower category should be control group
    local exp "opt noprefix"
    local if "opt"
    local in "opt"
    local options "By(string)"
    local varlist "req ex max(1)"
    parse "`*'"
    if "`exp'"!="" {
         if "`by'"!="" {
              di in red "may not combine = and by()"
              exit 198
         }
         confirm var `exp'
         quietly sum `varlist' `if' `in'
         local n1 = _result(1)
         local u1 = _result(3)
         local s1 = sqrt(_result(4))
         quietly sum `exp' `if' `in'
         local n2 = _result(1)
         local u2 = _result(3)
         local s2 = sqrt(_result(4))
         if `s1'==. { error 2001 }
         modti `n1' `u1' `s1' `n2' `u2'
         exit
    }
    confirm var `by'
    quietly tab `by' `if' `in'
    if _result(2)!=2 {
         di in red "`by' takes on " _result(2) " values, not 2"
         exit 450
    }
    tempvar M TOUSE
    quietly gen byte `TOUSE' = 1 `if' `in'
    sort `by' `TOUSE'
    quietly by `by' `TOUSE': gen byte `M'=cond(_n==1,1,.) if `TOUSE'==1
    sort `M' `by'
    quietly sum `varlist' if `by'==`by'[1] & `TOUSE'==1
    local n1 = _result(1)
    local u1 = _result(3)
    local s1 = sqrt(_result(4))
    quietly sum `varlist' if `by'==`by'[2] & `TOUSE'==1
    local n2 = _result(1)
    local u2 = _result(3)
    if `s1'==. { error 2001 }
    modti `n1' `u1' `s1' `n2' `u2'
end