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st: mi impute: VCE is not positive definite


From   chong shiauyun <shiauyun416@hotmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: mi impute: VCE is not positive definite
Date   Tue, 30 Oct 2012 13:53:16 +0800

Hello all, 
I was using -mi impute chained- to impute my dataset. I have trouble with the variable citwlc_i, which is an interaction of cit*wlc. (cit is my temperament categories(3) and wlc is parentalal warmth latent class). I received the following error message:


mi impute: VCE is not positive definite 
    The posterior distribution from which mi impute drew the imputations for citwlc_i is not proper when the VCE estimated from the observed data is
    not positive definite.  This may happen, for example, when the number of parameters exceeds the number of observations. Choose an alternate
    imputation model.

I am not sure why this happens and what should I do to make the model works.Please advice. 

My code is:
mi impute chained (reg) birthweight tempcatwlc_i tempcatclc_i pvlwlc_i pvlclc_i tempcat2wlc_i tempcat2clc_i citwlc_i citclc_i (ologit)alcpreg3 kb280 ke016_b2 ke017_b2 kf300_b kf323_b kf351_b kf352 kj250_b kj265 kj289 kj290 kj373_b2 kj374_b2 sosprt scmatpat3 ednmatpat (logit)sex ethnicity smkpreg marist findiff hhcrowd matdepr patdepr mumhealth ke015_b ke014_b kg255_b kj425_b j564_b (truncreg, ll(45) ul(151))totaliq (truncreg, ll(46) ul(155))verbiq (truncreg, ll(46) ul(151))perfiq (truncreg, ll(55) ul(134))fh9481 (truncreg, ll(0) ul(60))kb800a (truncreg, ll(0) ul(50))kb801a (truncreg, ll(0) ul(50))kb802a (truncreg, ll(0) ul(50))kb803a (truncreg, ll(4) ul(50))kb804a (truncreg, ll(0) ul(45))kb805a (truncreg, ll(0) ul(35))kb806a (truncreg, ll(0) ul(50))kb807a (truncreg, ll(1) ul(50))kb808a (truncreg, ll(0) ul(45))ke800a (truncreg, ll(0) ul(55))ke801a (truncreg, ll(0) ul(55))ke802a (truncreg, ll(0) ul(35))ke803a (truncreg, ll(4) ul(45))ke804a (truncreg, ll(0) ul(60))ke805a (trunc!
 reg, ll(0) ul(45))ke806a (truncreg, ll(0) ul(50))ke807a (truncreg, ll(1) ul(40))ke808a = mumage babygestation,add(20) rseed(11349730) noisily augment burnin(30) chainonly savetrace(mydata, replace) dryrun report

Thanks in advance!

Shiau

 		 	   		  
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