Four conditions - One pool of stimuli

[David McFarlane]

Emmet,

Stock reminder:  1) I do not work for PST.  2) PST's trained staff 
takes any and all questions at 
http://support.pstnet.com/e%2Dprime/support/login.asp , and they 
strive to respond to all requests in 24-48 hours -- this is pretty 
much their substitute for proper documentation, so make full use of 
it.  3) If you do get an answer from PST Web Support, please extend 
the courtesy of posting their reply back here for the sake of others.

That said, here is my take...

Not sure that I follow your question, so I will answer one that I 
can.  Suppose you have a pool of 125 stimuli and, *within any one 
session*, you want to sample 25 at a time randomly without 
replacement (i.e., no stimulus reused either within any sample of 25 
nor until all 125 stimuli are sampled).  You can do this very easily 
with a nested List.  Just put all your stimuli in their own nested 
List, say, StimList.  Set that List to Random.  Now, in any other 
List where you want to use stimuli from StimList, simply add StimList 
in the Nested column, and then use the attributes from StimList just 
as you normally would.  You can have one main List take 25 samples 
from StimList, and later take another 25 samples, and it will pick up 
right where it left off.  IOW, E-Prime essentially shuffles all 125 
stimuli, and then "draws" from that shuffled List until the List is 
exhausted, and then reshuffles the List and starts over.  Or, you can 
get other effects by changing settings under the List Reset/Exit tab.

In general, just think of Lists (whether nested or not) as decks of 
playing cards, that's how I have come to understand them.  Think of 
nested Lists as just additional, separate decks of cards that get 
drawn from whenever you draw a row from a main List that names a 
nested List.  I have written about this elsewhere, if you search 
around you may find my earlier posts here or on the PST Forum, but 
here is another attempt...

So, each "card" (row) in any "deck" (List) has some attribute values 
written on it; some of those may be the names of other decks (nested 
Lists) to draw from.  So, you start by shuffling all these decks as 
needed.  Then you draw a card from a "main" deck, and read off the 
attribute values written on it.  If any of these names another deck, 
you draw a card from those decks and read off those attribute values; 
once again, if any of these names another deck then you draw from 
that deck, etc.  When you are done you will have a set of attribute 
values to work with for that trial.  At the end of the trial you put 
all the cards that you drew onto a discard pile for each deck, and 
then draw new cards.  Whenever you exhaust any deck, you pick up its 
discard pile, reshuffle that deck as needed, and carry on.

It gets a little more complicated than this because you can modify 
this behavior by changing the settings under the List Reset/Exit tab, 
but this is a pretty good first approximation.

Now, if you want samples of 25 to take place *across* separate 
sessions, well, that is an entirely different and more complex 
matter.  Could be done, but no sense trying to explain that now.

-- David McFarlane, Professional Faultfinder
"For a successful technology, reality must take precedence over 
public relations, for nature cannot be fooled."  (Richard Feynman, 
Nobel prize-winning physicist)


At 6/14/2011 12:18 PM Tuesday, you wrote:
>Hi all,
>
>I have battled through the entire user guide and I am definitely
>getting places with my E Prime project but I have one sticking point I
>hope you can help me with. I have a within-groups design with four
>groups (and one practice condition) and each condition will receive 25
>picture slides. I think that my answer may lie within the nested lists
>option but I'm struggling to a find a way to have each of the
>conditions randomly sample (without replacement) their 25 pictures
>from the same 125 picture list so that, in effect, each participant,
>regardless of the counterbalancing of conditions has a unique ordering
>of the stimuli from start through finish.
>
>Please let me know if I have not explained myself clearly or if you
>would like me to post up a screenshot or something (can I do that?)
>
>many thanks in advance,
>
>Emmet Clarke
>
>University of York

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