E-Prime: sampling half of the items in a list, then coming back for the rest later (+nesting)

[David Vinson]

Dear List,

I am running into a brick wall in E-Prime design/setup and I suspect I 
am missing something obvious.

My experiment has two blocks: one block uses words of type A, and one 
block uses words of type B.
Both blocks also include words of type C, sampled from a list twice as 
large as A or B.

To complicate matters (of course), all words are paired with pictures 
within a block, three repetitions of each word with one (and only one) 
picture of type P, one of type Q and one of type R.

My current experimental design has two levels of nested lists for a 
given block. For block type A, the relevant parts of the List look 
something like this:

Top level List for block 1:
Weight Nested
24     WordListA
24     WordListC

WordListA
Weight Nested    String
1      PictureP   foo
1      PictureQ   foo
1      PictureR   foo
1      PictureP   bar
1      PictureQ   bar
1      PictureR   bar
etc

Word lists B and C are also structured in the same manner, thus 
specifying that each word will appear with one example of PictureP, one 
example of pictureQ, and one example of pictureR in the course of the 
experiment (we don't care which pictures within a group). All lists are 
sampled randomly without replacement, and each word occurs three times 
in the course of the experiment.

Our problem is related to trying to balance degree of word repetition 
within a block.
With the above setup, block 1 will include exactly 3 occurrences of each 
word of type A, paired with a picture of the desired type (that is, 
WordListA will be completely exhausted).   However, the same block will 
include variable numbers of occurrences of word type C since only half 
this list is being sampled.

We wish instead to include only half the words of type C in a given 
block, thus fully exhausting the word-picturetype combinations before 
moving to the second block. That is, subdividing list C into two equally 
sized sublists, with different items assigned randomly per subject.

So, does anyone have suggestions of how we might do this?  I know one 
way - create a mess of separate .es files, one for each subject, 
randomly generating C-sub-1 and C-sub-2 for each.   But I would really 
like to do this within a single .es file if (reasonably) possible.  Any 
suggestions would be very welcome indeed.


Thanks!
david
-- 
David Vinson, Ph.D.
Senior Postdoctoral Researcher
Cognitive, Perceptual and Brain Sciences Research Department
University College London
26 Bedford Way, London WC1H 0AP
Tel +44 (0)20 7679 5311  (UCL internal ext. 25311)

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