# mne.combine\_evoked weights

**URL:** <https://mne.discourse.group/t/mne-combine-evoked-weights/6732>\
**Category:** Support & Discussions\
**Created:** [April 17, 2023, 3:32pm UTC](https://mne.discourse.group/t/mne-combine-evoked-weights/6732 "2023-04-17T15:32:06Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![aalt](https://avatars.discourse-cdn.com/v4/letter/a/779978/32.png) [@aalt](https://mne.discourse.group/u/aalt)\
**Post date:** [April 17, 2023, 3:32pm UTC](https://mne.discourse.group/t/mne-combine-evoked-weights/6732/1 "2023-04-17T15:32:06Z")

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Hello, I have some questions regarding the mne.combine\_evoked() function.  
I would like to combine evokeds in order to compare them as follows:  
let’s say I have 4 conditions a1, a2, b1, b2, and I want to combine a1 and a2 as a same condition, as well as for b1 and b2 as a single condition, to be able to compare condition a to condition b.  
How should I weight those ?  
`mne.combine_evoked([evokeds[a1],evokeds[a2], evokeds[b1],evokeds[b2], weights=[1,1,-1,-1])`

Is this correct?

Thank you

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**Author:** ![richard](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/richard/32/15_2.png) [@richard](https://mne.discourse.group/u/richard)\
**Post date:** [April 17, 2023, 5:10pm UTC](https://mne.discourse.group/t/mne-combine-evoked-weights/6732/2 "2023-04-17T17:10:05Z")

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Hello,

> [@aalt](#):
>
> mne.combine\_evoked([evokeds[a1],evokeds[a2], evokeds[b1],evokeds[b2], weights=[1,1,-1,-1])

I’d think that this is the correct approach, yes.

Best wishes,  
Richard