Evenly, yet randomly, distributing cells

[laurenatlas]

Hi,

I'm trying to design a neuroimaging task in which I have 6 runs of 8
trials (2 presentations of 4 stimuli: A,B,C,D) each. I'm setting up my
design matrix using excel, with runs in six columns and trials in eight
rows.

In my first column, I need to constrain the first two rows to either A
or B. Other than this, I'd like to randomly present two of each item
in each column. I was going to stop here, and just use a RAND function
to pair with and sort each of the 6 columns. However, I just learned
that I need to also take into account possible order effects, and make
sure that across the columns, I make sure each condition appears at
least once. I have NO idea how to set up a function in excel that can
ensure both of these parameters... Does anyone have any idea how to do
this? I've tried to search across this forum, but I'm having a hard
time finding it with proper search terms.

Thank you for any help you can offer!

Lauren

PS. I also have access to matlab, if that would help me at all...

 

[laurenatlas]

Sorry, I should clarify... I mean that within each row, I need to make
sure all 4 conditions appear. Within each column, I need to make sure 2
of each condition appears. Does that make it clearer?

Thanks!
Lauren

 

[Jim Cone]

Lauren,
Your problem got my interest.
I am not sure how the first two rows fit in with
your minimum occurrence requirement.
In any case I put together a single sheet workbook using
VBA and formulas that puts random pairs on the
8 row x 6 column grid that meets the minimums.
If you would like a copy let me know.
Remove XXX from my email address.
(e-mail address removed)
--
Jim Cone
San Francisco, USA
http://www.realezsites.com/bus/primitivesoftware


<[email protected]>
wrote in message
Sorry, I should clarify... I mean that within each row, I need to make
sure all 4 conditions appear. Within each column, I need to make sure 2
of each condition appears. Does that make it clearer?
Thanks!
Lauren