Hi George,

I wouldn't quite say this is a consequence of censoring,
as the principle culprit is likely band passing. What is
your TR? And how many time points are you staring with?

Well, since you say that subjects start failing at about
70%, I will guess that your TR is 2s, and you have on the
order of 160 time points.

Most people ignore the fact, but for a TR of 2s, the cost
of bandpassing is 60% of the degrees of freedom up front.
If censoring costs another 30% and motion, derivatives,
and polorts cost another 10% (~16 regressors), there goes
100% of the degrees of freedom. And it can get worse...

And to put it another way, if the typical subjects has
only 15% of the time points censored, then they will be
left with about 15% (24?) degrees of freedom for the
correlation analysis. That is not a lot.

For these reasons, I consider band passing the main
culprit.

- rick