R help - Jul 2011 - The test of randomized slopes(intercepts)

Hi all:
I perform the linear mixed model for 300 persons, y is CD4 count,x is time.
 
I randomized slope and intercept,so I can get 300 slopes and 300 intercepts.Now
I wanna test wheter the variance of 300 slopes and 300 intercepts differs from
zero. If the variance of 300 slopes(or intercepts) differs from zero at 0.05
significant level,I should randomize the slope(or intercept), and if not,I
should fix the slope(or intercept).
But I can't find out which statistical test should be used to test whether
the variance of 300 slopes(or intercepts) differs from zero,which need your
help.
 
Thanks a lot!
My best.
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