# Empirisoft Support

1. Contributing Member Join Date
Nov 2006
Posts
19

## Latin square design

I've got an experiment that I'm designing, and I've got the following issue. I'd like to present a video before a series of questions, but I'd like to choose from sets of videos to present. So, I've got four sets of four videos each, and I'd like to present one out of each set at random, and I'd like each of the set representatives to be presented in random order. Does that make sense?

Set 1 (a,b,c,d)
Set 2 (e,f,g,h)
Set 3 (i,j,k,l)
Set 4 (m,n,o,p)

The questionnaire should randomize sets 1-4, and when a set is presented, a single video is chosen at random from that set. So,

Set2 g
Set3 l
Set1 d
Set4 p

and

Set 3 k
Set 1 b
Set 4 o
Set 2 f

are both possible presentations.

Is this kind of randomization possible in MediaLab?  Reply With Quote

2. Blair Jarvis, Administrator Join Date
Nov 2005
Posts
3,318
Yes, you can assign a constant BGR (between groups randomization) value to all the videos within a single set like this:

Set 1 (a=1,b=1,c=1,d=1)
Set 2 (e=2,f=2,g=2,h=2)
Set 3 (i=3,j=3,k=3,l=3)
Set 4 (m=4,n=4,o=4,p=4)

That will keep the sets together but will randomize the set order (e.g., set 2, set 3, set 1, set 4).

Then assign constant WGR (within groups randomization) value to all the videos within each set in the same manner:

Set 1 (a=1,b=1,c=1,d=1)
Set 2 (e=2,f=2,g=2,h=2)
Set 3 (i=3,j=3,k=3,l=3)
Set 4 (m=4,n=4,o=4,p=4)

That will randomize the order of the videos within each set, e.g., Set 1 (c, d, a, b).

The trick now is to present just one video from each set and not all four. Pretty easy--just insert an instruction screen at the end of each block. For every item within the block--have it skip automatically to that end item. This way, no matter which stimulus is shown first, MediaLab will then skip to the end of the set--voilà!

Ok, it might be way easier to see an example.. Take a look at the illustration I've posted below.

-Blair  Reply With Quote

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