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Please which code can i use to test for random effects (random intercepts and random slopes) using a mixture of chi sqaures
Thanks
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I am not sure if the following CHISQ option is what you are looking for ?
proc mixed data=sashelp.heart(obs=100) ;
class bp_status sex;
model weight=height sex/s chisq;
random int sex/subject=bp_status ;
run;
or @SteveDenham @lvm knew it.
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I think you are asking about testing Ho: Variance = 0 vs Ha: Variance >0. When you use the COVTEST statement in GLIMMIX, the procedure automatically uses a mixture of chi-square statistics when appropriate (and it tells you in the results). The mixture is typically needed when the variance parameter is on the boundary (e.g., 0).
See
https://support.sas.com/kb/40/724.html
to learn about COVTEST (this is different than the covtest option in MIXED). The online documentation for GLIMMIX will explain COVTEST in more details, with simpler examples. This is a likelihood ratio test, where the ratio is compared with the chi-square statistic (mixture or otherwise, depending on the situation). This is explained also in:
chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://support.sas.com/resources/papers/proceedings/proceedings/forum2007/177-2007.pdf