I have non-normally distributed dataset, a record of a parameter, e. g. 50 subjects reacted to stimulation, (9 periods of time in total). So I have a matrix of 50x9 numbers, 9 medians for each time-period for each volunteer. When I plot the above data, subjectively I see that there is some division, a part of subjects reacted to stimuli with a delay (differences in parameter change in 4th period rather than 3rd). I am trying to find a statistical way to check if there are these groups (to check for correlations with other parameters later( psychological stats)). Actually, should I test for bi or multimodality? I am using Matlab and Statistica
I will be grateful for any ideas.
Upd.: The record of several physiological parameters (sweating, temperature, etc, changes in those as a response to emotionally-negative footage). There were rest-stimulation-rest phases, the recording of physiological data was performed continuously