[pymvpa] Balancing strategy

[Yaroslav Halchenko]

On Mon, 25 Nov 2013, Chris Johnson wrote:
> I have an experimental (fMRI) paradigm wherein the conditions were
> balanced across runs, and performed a searchlight MVPA analysis with
> leave-one-run-out cross validation. In some subjects, however, we found
> excessive head motion and had to eliminate scans

before jumping to rebalancing:

was such periods motion associated just with few consecutive volumes?

if so -- and if you are using some GLM modeling first to extract betas
for your MVPA analysis -- you could also 'drop' those volumes by adding
additional single-time-point regressors into your GLM model, so that
would account for those volumes effects, while still providing you
estimates for the explanatory variables of interest.  This way you might
avoid eliminating complete trials from your further MVPA and thus not
requiring re-ballancing

-- 
Yaroslav O. Halchenko, Ph.D.
http://neuro.debian.net http://www.pymvpa.org http://www.fail2ban.org
Senior Research Associate,     Psychological and Brain Sciences Dept.
Dartmouth College, 419 Moore Hall, Hinman Box 6207, Hanover, NH 03755
Phone: +1 (603) 646-9834                       Fax: +1 (603) 646-1419
WWW:   http://www.linkedin.com/in/yarik