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Thread: Repeating stimuli when using $ random selection in stimlist (case 467)

  1. #1
    Join Date
    Aug 2008
    Posts
    4

    Repeating stimuli when using $ random selection in stimlist (case 467)

    Hi,
    I saw an old thread with this title, but the solution there did not apply to my files:
    I'm using both WGR and $ in my IAT blocks. I want to present stimuli which are texts of 4 different groups, randomizing between group a and group b, then between group 1 and group 2, but presenting stimuli so participants see first stimuli from wither a/b, then 1/2, alternately (for example: 1-b-2-b-1-a-1-b).
    then in addition, each of these groups include 5 stimuli I want to present in random, without replacement.
    What actually happens is that participant ends seeing the same stimuli presented as though randomization was done with replacement. It doesn't just seem that way because all stim were used once, since it can happen even in the beginning of a block (see block2).
    What I think may have happened, is that the $ randomization was done first, and then the wgr randomized trials again, and then changed the order and then- even though randomization WAS done without replacement, same stimuli were presented one after the other because of the wgr.
    Am I right? is there a possibility of making directRT first choose the group of words THEN a word within it without replacement?
    I'm sorry about the length, but I'll appreciate any ideas, and I'm enclosing both input and output files, output shown by order presented to participant.
    Thank you very much in advance
    Ariela
    Attached Files Attached Files
    Last edited by jason_reed; 12-08-2015 at 06:23 PM.

  2. #2
    Join Date
    Feb 2013
    Posts
    1,090
    Based on the example .csv input file you attached, simply switch you nonzero positive integers from the wgr field to the bgr field. This will make DirectRT treat each set of trial rows with the same nonzero positive integers as single group of trials; just make sure that all of the rows with the same nonzero integer are contiguous in the .csv input file. DirectRT will randomize the presentation of these groups. Your use of the stimlists with $ will then randomly select items from the stimlists without replacement.
    Jason Reed
    Empirisoft Software Support Specialist

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