[FieldTrip] 3x2 cluster-based permutation and random seed

[Annie Menart]

Dear Fieldtrippers,

We are currently adapting a 2 group by 2 condition cluster-based permutation to be a 3 group by 2 condition cluster-based permutation. Following the documentation, we are subtracting the conditions to test the interaction. Does the code below look like a valid way to do this? It's running correctly and we don't get errors, but we wanted to make sure, since it differed from the setup of the K-by-L example.

Example code from the 2x2 documentation :

cfg = [];
cfg.parameter = 'powspctrm';
cfg.operation = 'subtract';
GAdiff11_12 = ft_math(cfg, GA11, GA12);
GAdiff21_22 = ft_math(cfg, GA21, GA22);

...

[stat] = ft_freqstatistics(cfg, GAdiff11_12, GAdiff21_22);

Our adaptation of the example code to be a 3x2 interaction:

cfg = [];
cfg.parameter = 'powspctrm';
cfg.operation = 'subtract';
GAdiff11_12 = ft_math(cfg, GA11, GA12);
GAdiff21_22 = ft_math(cfg, GA21, GA22);

GAdiff31_32 = ft_math(cfg, GA31, GA32);

...

[stat] = ft_freqstatistics(cfg, GAdiff11_12, GAdiff21_22, GAdiff31_32);


Secondly, for cluster-based permutations (ft_freqstatistics), can you set the seed using cfg.randomseed? In the documentation, we've seen it used for ft_componentanalysis, but we weren't sure if it also worked for ft_freqstatistics. We have it running with no errors, but wanted to make sure since we didn't see the parameter cfg.randomseed used directly in ft_freqstatistics. If not, is there a way to set the seed?

Best,
Annie
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