[R] Why random item need grouping symbol '|' ? And why is there no '|' in fixed item in lme?

From: <fanzhang2_at_gmail.com>
Date: Wed 03 May 2006 - 03:34:07 EST

Hi everyone,

What's the difference between the following two linear mixed models? Supposed productivity scores is decided by three types of machines as used by six different workers.

scoreij=workeri+machinej+eij i=1,2,...6 j=1,2,3

machine = as.factor(machine)
worker = as.factor(worker)
lme(fixed=score~machine, data=example1, random=~1|worker)

My question is what is the difference between the above lme and the following lme? Why is there no '|' in fixed item in lme?

lme(fixed=score~machine, data=example1, random=~worker)

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