[Eeglablist] Permutation stats and number of trials per condition

[Jenson, David Evans]

EEGLABers,

I’m working through reviewer comments, and have a question about how permutation stats are run in EEGLAB.

I’m looking at ICA-decomposed ERSP differences across 7 conditions (42 participants), each of which has a different number of usable trials based on participant accuracy and noisiness of the data.  The reviewer is concerned because there is a significant difference in the number of trials across conditions, stating that comparisons between conditions are unfair since the signal to noise ratio is higher in the condition with more trials.

Based on the use of permutation statistics, I don’t think this is a valid concern, but I am having trouble articulating why.  Can anyone help with:

1: Confirming that an unequal number of trials across conditions is not problematic?

2: Helping me understand how permutation statistics address the issue?

Thanks,

David Jenson, PhD
Assistant Professor
Department of Speech and Hearing Sciences
o: 509-368-6913 | david.jenson at wsu.edu<mailto:david.jenson at wsu.edu>