(any comments on how I can edit the question and improve its clarity, if lacking, are welcome!)

I have data from a study in which subjects were listening to a musical piece and asked to press a key at certain moments. Each 5-second period (epoch) in the piece has been labelled as type A, B or C, with adjacent 5-second epochs not necessarily of the same type.

I then computed a keypress count within each 5-second epoch in the piece, and thus obtained several values for each epoch type (A,B,C).

I would like to do a statistical test between these group means to check for a significant difference, but the problem is that there is an unequal number of elements (epochs) in each of the 3 groups. I think a repeated-measures ANOVA is therefore probably unsuitable.

I also think based on this past CV post that the unequal-number-of-elements-in-each-group problem can be overcome by computing pair-wise differences when such pairs can be defined, and then running paired-samples t-test on the difference (A vs B, B vs C, A vs C). However, I am not sure this data is truly "paired" since the data points are 5-second epochs from various parts of the piece; or even really "repeated measures" in the traditional sense!

Does it even make sense to run a statistical test in this case, and if so, which test is appropriate?