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2 weeks ago

Hello,

I am trying to measure the difference in change of eGFR (postindex_egfr) between treated (cohort_num=1) and untreated (cohort_num=0) groups. I am using a repeated measures mixed model to study this association and eGFR values have been divided by quarter (over 5 years). A lot of quarters will have missing eGFR values.

There are no duplicate values by quarter for any given patient. The code is written below and I'm getting an infinite likelihood error. Advice would be appreciated.

proc mixed data=hcvrenal.analysis_set_3 method=reml covtest;

class patid cohort_num (ref='0') gender bus_num dm(ref='0') htn(ref='0') ccf(ref='0') mi(ref='0') pvd(ref='0') cva(ref='0') can(ref='0') abuse(ref='0')

hiv hbv ftg(ref='0') ckd_stage(ref='1') quarter (ref='1');

model postindex_egfr = cohort_num ageatindex gender bus_num

dm htn ccf mi pvd cva can abuse hiv hbv ftg

fib4 ckd_stage

QUARTER indexdate /s ddfm=satterth COVB ;

WHERE QUARTER IN (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20);

RANDOM patid/cl;

repeated quarter/type=ar(1) subject=patid*cohort_num ;

lsmeans cohort_num/cl;

estimate 'Change from baseline to quarter 4' quarter

-1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0/e cl;

estimate 'Change from baseline to final eGFR' quarter

-1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1/e cl;

run;

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2 weeks ago

I'm not familiar with this procedure but you missed posting the ERROR you got.

Please post, too, the log and any results you got, marking the errors.

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2 weeks ago

Here is the log:

WARNING: Class levels for patid are not printed because of excessive size.

NOTE: 20364 observations are not included because of missing values.

WARNING: ODS graphics with more than 5000 points have been suppressed. Use the PLOTS(MAXPOINTS= )

option in the PROC MIXED statement to change or override the cutoff.

**WARNING: Stopped because of infinite likelihood.**

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2 weeks ago - last edited 2 weeks ago

I have googled for: **sas proc mixed infinite likelihood**

it seems to me that next link may help:

__Next lines were copied from that link page:__

An infinite likelihood during the iteration process means that the Newton-Raphson algorithm has stepped into a region where either the or matrix is nonpositive definite. This is usually no cause for concern as long as iterations continue. If PROC MIXED stops because of an infinite likelihood, recheck your model to make sure that no observations from the same subject are producing identical rows in or and that you have enough data to estimate the particular covariance structure you have selected. Any time that the final estimated likelihood is infinite, subsequent results should be interpreted with caution.

You may understand it better than me.

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2 weeks ago

There could be some helpful tips here

http://support.sas.com/resources/papers/proceedings12/332-2012.pdf

and

http://support.sas.com/resources/papers/proceedings15/SAS1919-2015.pdf

I have found that rescaling the response can be miraculous (sometimes anyway).

You may have collinearity problems with the predictor variables (both continuous and categorical).

You could start with a basic model that includes only a minimal number of predictors (i.e., cohort_num and quarter). If that converges, then you have something to work with. If it doesn't then that may point you towards a potential problem with patid.