[R] Please help a struggling student with data set-up for lmer crossed random effects

[Ralitt]

Hi all, 
I am just starting my first models in R and am having trouble with some of
the basics.

The main things at the moment are about setting up my data correctly.  I
have a repeated measures design-all participants complete 4 experimental
conditions. I want to fit a linear mixed effects model with crossed random
effects for subject and item. I have 4 conditions, 6 items per condition.
Because each condition uses different items, there are 24 total items. Each
group of 6 items only occurs in 1 condition, and it occurs in the same
condition for all participants. I am interested in including item as a
random effect in my model. My question is about labelling the items
correctly-should I label them 1-24, or 1-6 for each condition? I'm afraid if
I label 1-6 for each condition it will think item 1 was the same item and
was repeated in each of the four conditions. But if I label it 1-24 it will
look as though 18 of the items are missing in each condition as 6 can only
occur in any one condition. So, should I have my data like this:
subject	item		condition
1		1		1
1		2		1
1		3		1
1		4		1
1		5		1
1		6		1
1		1		2
1		2		2
1		3		2
1		4		2
1		5		2
1		6		2
1		1		3
1		2		3
1		3		3
1		4		3
1		5		3
1		6		3
1		1		4
1		2		4
1		3		4
1		4		4
1		5		4
1		6		4

or like this:

subject	item		condition
1		1		1
1		2		1
1		3		1
1		4		1
1		5		1
1		6		1
1		7		2
1		8		2
1		9		2
1		10		2
1		11		2
1		12		2
1		13		3
1		14		3
1		15		3
1		16		3
1		17		3
1		18		3
1		19		4
1		20		4
1		21		4
1		22		4
1		23		4
1		24		4

Sorry for the basic question, but I can't seem to figure this out!



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