topic ERROR: Within-imputation COVB matrix has diagonal entries less than 0 for _Imputation_= 868 in in SAS Programming

ERROR: Within-imputation COVB matrix has diagonal entries less than 0 for _Imputation_= 868 in

cdriesse139 — Wed, 20 Sep 2023 20:18:23 GMT

Hello you all,

I have been trying to impute missing data using the delta adjusted pattern imputation to compare it to the control-based pattern imputation.

Unfortunately I am getting the above error message which I am unable to solve. Could somebody advice?

My syntax is as follows:

proc mi data=milk.missingwide out=milk.FNDSdimp seed=128 nimpute=1000;
class sex single precovid randomization;
FCS discrim(sex/details) discrim(single/details) reg(FNDSbase/details) reg(FNDS1/details) reg(FNDS2/details) reg(FNDS3/details) reg(FNDS4/details);
mnar model(FNDSbase / modelobs= (randomization='0'))
adjust (FNDS1/ shift=1 adjustobs=(randomization='1'))
adjust (FNDS2/ shift=1 adjustobs=(randomization='1'))
adjust (FNDS3/ shift=1 adjustobs= (randomization='1'))
adjust (FNDS4/ shift=1 adjustobs= (randomization='1'));
var sex single precovid FNDSbase FNDS1 FNDS2 FNDS3 FNDS4;
run;

*reverting back to long dataset type;
data milk.FNDSdimplong;
set milk.FNDSdimp;
week=1; FNDS=FNDS1; output;
week=2; FNDS=FNDS2; output;
week=3; FNDS=FNDS3;output;
week=4; FNDS=FNDS4; output;
run;

proc mixed data=milk.FNDSdimplong;
class subj randomization sex single week precovid;
model FNDS = randomization|week FNDSbase sex single precovid /ddfm=kr2 solution covb;
repeated week / subject=subj(randomization) type=AR(1) ;
rANDOM subj(randomization);
by _imputation_;
lsmeans randomization*week /pdiff cl;
ods output SolutionF=milk.mxFNDSdparms covb=milk.mxFNDSdcovb;
run;

proc mianalyze parms(classvar=full)=milk.mxFNDSdparms covb(effectvar=rowcol)=milk.mxFNDSdcovb;
class randomization week sex single precovid;
modeleffects randomization week randomization*week FNDSbase sex single precovid;
run;

Re: ERROR: Within-imputation COVB matrix has diagonal entries less than 0 for _Imputation_= 868 in

ballardw — Wed, 20 Sep 2023 21:27:31 GMT

We generally recommend including the code and and all the messages from the LOG when discussing errors so we can see exactly where SAS reported something and possibly other relevant information.

I this case look at your data for _IMPUTATION_=868 in data=milk.FNDSdimplong.

I suspect you will find something odd about the set of model variables for those observations.

Re: ERROR: Within-imputation COVB matrix has diagonal entries less than 0 for _Imputation_= 868 in

cdriesse139 — Thu, 21 Sep 2023 09:25:46 GMT

Thank you for your advice. Taking a closer look at the log indeed provided an answer to the question. While the covariance matrix that was the best fit for the non-imputed data, this covariance matrix was no longer the best fit when missing data was imputed.
Always good to see it with a fresh pair of eyes.