Randomization with constraints

[jarvis24]

David--such a list would be welcome! I would request that you direct the curious distinctions to the suggestions and feedback areas. That's where we go first when considering improvements for future versions.

[lisken]

I'm attempting to randomize presentation items, each of which gets presented a total of three times, with the constraint that an item will not immediately follow itself. Is there a way to do this in MediaLab? I can't seem to figure out how to harness "if" to make this work.
Many thanks for any suggestions!

[jarvis24]

Try creating a simple sample with say 6 items-2 words, used 3 times each (cat, cat, dog, dog, mouse, mouse). Then try to create a responses.xls file that does the randomization with constraints (such that one never follows itself). When you hit a roadblock, attach the file, and I'll take a look at it. Once it works with 6 items, it ought not be hard to expand it. I think it would simply be a matter of picking the first word, then picking the next, checking to ensure it's not the same as the previous word and so on. If it is the same then you pick again until it does not match. The only problem you need to account for beyond that is running out of words such that when you have only one word left, it happens to be the same as the second last word. In such a case, you would need to add a condition to start over. As I said though, try your best and then attach it here if/when you get stuck.

[trab24]

I have the same problem. I am using DRT 2010? has this issue been solved? maybe using excel power?

Thanks.

[trab24]

Hi, I found a work around for this.
Say I have a group of 4 pictures that must be displayed 3 times in random order with no overlap (4 pics, 4 pics, 4 pics). Instead of using list of stimuli I use WGR to randomize by assigning each repetition of the 4 items a WGR. Then select one of the pics and assign it a WGR or 0 in all repetitions. by strategically positioning that pic overlap can be avoided. So it would look like this (working with pic 3):
WGR STIMULI
1 pic 1
1 pic 2
1 pic 4
0 pic 3
______________________
2 pic 1
2 pic 2
0 pic 3
2 pic 4
_______________________
0 pic 3
3 pic 1
3 pic 2
3 pic 4

It's not pure randomization but it works for me.

[Dianna]

I am having a similar issue with an experiment I want to run with directRT 2010.

I am trying to randomize a task in which there are 24 trials with sets of images within each trial. There are images of 4 people, each with 6 different types of images (which make 24 trials in total). I want to make it so that all 4 of the same type of image do not occur all within the first half or all within the second half of the task. I do not want to constrain it so much by making 2 blocks and putting 2 of the people within the same block, and then just randomizing the order of the blocks (because there may be some effect of always putting the same 2 people together). Do you have any suggestions as to how I could do this?