Hi Experts!

I have a statistical question. I will be carrying out a first level analysis on a set of task-fMRI data with two conditions, i.e. condition high - with stimulus that appear 70% (420 trials across 4 blocks) of the time, and condition low - with stimulus that appear 30% (180 trials across 4 blocks) of the time.

The event-related trial sequence is designed with genetic algorithm (Wager and Nichols, 2003) to maximise statistical power.

Given the nature of the the two conditions, the high condition will have alot more trials than the low condition. Is it necessary to balance the number of trials between the two conditions in the analysis?

This could be done by randomly sampling and discarding trials from the high condition. However, this means I will loose more than half of the trials in the high condition.

What are your thoughts on this?

Thank you!