st: bootstrap and singleton

["R.E. De Hoyos" <redeho@hotmail.com>]

Statalist,

I am trying to get bootstrapped SE from estimates that control for survey 
design. I am using the
-bsample- command with the strata() option. Since I have some singleton 
strata, after every re-sampling I temporary delete the singleton strata. 
However when using my code I (sometimes) get the singleton error. I've been 
going to my code using -set trace on- command but I cannot see anything 
wrong with it. When the error occurs it is just after the _robust estimation 
withing -svy- takes place.

Any thoughts?

Many thanks,

Rafa
PS. I include part of the code:

syntax varlist [if] [in], SELect(string) [SHOWmlogit BOOTstrap(string) 
MLOPtions(string)]

tokenize `varlist'

local y `1'

tokenize `bootstrap', parse(" ")

local K `1'

tempvar singleton

tokenize `select', parse("=")

local m `1'

macro shift

local z `2'

qui svyset

singleton `varlist' `z', strata(`r(strata)') gen(`singleton')  //programme 
to identify singleton

if "`bootstrap'"=="" {

qui sum `singleton'

if `r(max)' == 0 {

base `varlist' `if' `in', select(`select')  `showmlogit' 
mloptions(`mloptions')

}

else {

preserve

qui drop if `singleton'==1

noi di in yellow "`r(sum)' strata with single PSU detected and excluded from 
the estimation"

base `varlist' `if' `in', select(`select')  `showmlogit' 
mloptions(`mloptions')

restore

}

}

else {

tempname b bstrv

local k=1

while `k'<=`K' {

preserve

qui svyset

bsample, strata(`r(strata)')

tempvar singleton`k'

tokenize `select', parse("=")

macro shift

local z `2'

qui svyset

singleton `varlist' `z', strata(`r(strata)') gen(`singleton`k'')

drop if `singleton`k'' == 1

base `varlist' `if' `in', select(`select')  bootstrap mloptions(`mloptions')

tempname b`k'

matrix `b`k''=e(b)

if `k'==1 {

matrix `b'=`b`k''

}

if `k'>1 {

matrix `b'=`b'+`b`k''

}

restore

local k=`k'+1

}

local k=1

while `k'<=`K' {

if `k'==1 {

matrix `bstrv'=(`b`k'' - (`b'/`K'))'*(`b`k'' - (`b'/`K'))

}

if `k'>1 {

matrix `bstrv'=`bstrv'+(`b`k'' - (`b'/`K'))'*(`b`k'' - (`b'/`K'))

}

local k=`k'+1

}

matrix `bstrv'=`bstrv'/(`K'-1)
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/