What if there are no negative clusters?

Michael Wibral michael.wibral at WEB.DE
Fri Oct 8 15:21:49 CEST 2010


Hi Emanuel,

of course you have to use an alpha of 0.025 if you want to test both effect directions independently (as I assume). This is because you only know post hoc that there are no negative clusters. There is no way around it.

Michael

-----Urspr√ľngliche Nachricht-----
Von: "<Emanuel van den Broeke>" <e.vandenbroeke at ANES.UMCN.NL>
Gesendet: Oct 8, 2010 2:59:28 PM
An: FIELDTRIP at NIC.SURFNET.NL
Betreff: [FIELDTRIP] What if there are no negative clusters?

>Dear people
>Who can answer my question?
>
>So I understand that is always the best to test two-sided with the non-
>parametric permutation test, because one is interested in both directions of 
>the effect; so both the positive and negative clusters. but what if your 
>observed dat shows no negative clusters? There is no negative cluster 
>detected above the threshold. Do you still have to use an alpha of 0.025 then?
>
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