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Likelihood Ratio Test in Mixed Model

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Likelihood Ratio Test in Mixed Model

[ Edited ]
The likelihood ratio test of comparing reduced model with full model differs by fixed factor result to chi-square distribution of zero degree of freedom.
/* reduced model */
proc mixed method = ml;
class block gen;
model rtwt = /ddfm = kr;
random block gen;
run;
 
/* full model*/
proc mixed method = ml;
class block gen;
model rtwt = prop_hav/ddfm = kr;
random block gen;
run;
 
There are 3 degree of freedom from reduced model - block variance, genotype variance, and residual variance. The same degree of freedom for full model with includes prop_hav as covariate. The difference in their -2 loglikelihood has zero degree of freedom under chi-distribution. Please could anyone guide me on how to compare these model to ascertain if the full model is significantly different from reduced model.
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