Randomised sub-lists

[David McFarlane]

H,

I take it that you want randomized sequences that will continue 
across separate experimental runs.  That's a tall order for any 
system, as it would have to preserve and reuse information between 
sessions.  As Ben says, you would first have to reuse the same random 
seed between runs.  That alone would give each subject who uses the 
same random seed the same sequence.  If you want to have one subject 
run a random sequence of 60 items out of 360, and then the next 
subject run the next 60 items from that same random sequence, then 
you have to to a little more.  I think that I would start with 
reusing the random seed as already posited, and in additon use the 
Offset order for my List to start with the 61st item from the random 
sequence, or 121st, etc.  Just a thought.

You might also consider asking PST Web Support 
(http://support.pstnet.com/e%2Dprime/support/login.asp ) for ideas, 
they have come through for me on issues like this from time to 
time.  For all I know the new StartupInfo file mechanism of EP2 could 
help you with this.

-- David McFarlane, Professional Faultfinder


At 4/21/2010 01:43 PM Wednesday, ben robinson wrote:
>to do this you will probably need to manually assign a value for the 
>Random Seed for each 6 participants you see.
>the first 6 participants might be assigned a random seed of '1', the 
>next six '2', etc.  if you set it up properly your list of 360 
>stimuli will be shuffled according to the random seed value.
>you could then determine which subset of 60 items, drawn 
>pseudorandomly from the larger set of 360 items, to present to your 
>subject based on Subject Number.  divide the the subject number by 
>6, take the remainder which will always be a value from 0-5, and 
>based on that value present one of six different subsets.
>something like that.  sorry if it's not very clear...
>
>On Wed, Apr 21, 2010 at 11:53 AM, Hester 
><<mailto:hester.duffy at gmail.com>hester.duffy at gmail.com> wrote:
>Hi All,
>
>I'm trying to set up a study in which participants rate the stimuli
>used in another experiment. I have 360 stimuli in all, but I only want
>each participant to rate 60 of them, and I want to do this in such a
>way that each of the stimuli gets used the same number of times.
>Obviously I could just create 6 lists of 60 items each and use
>different run files each time, but I'm wondering if there's a more
>efficient and elegant way of doing it.
>
>I've tried setting the list to reset after a cycle of 360 samples, and
>to exit after 60, but having run it three times, and then compared the
>lists of stimuli used, I'm getting duplicates, so it's clearly not
>doing what I want. Basically, I need it to give the first participant
>a random list of 60 taken from the full list of 360; the second
>participant should then get a random list of 60 taken from the
>remaining 300, the next a random list of 60 from the remaining 240,
>and so on, until the sixth participant has a randomly-ordered list
>consisting of the remaining 60 items. It would then reset, so that the
>seventh participant gets a random list of 60 from the original 360
>(but not necessarily the same 60 as participant 1).
>
>Does anyone know whether E-Prime can do this, and if so, how?
>
>Many thanks,
>
>H

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