# Interpolate bad channels before or after CAR referencing?
**URL:** https://mne.discourse.group/t/interpolate-bad-channels-before-or-after-car-referencing/3696
**Category:** Support & Discussions
**Tags:** preprocessing, eeg
**Created:** [September 15, 2021, 8:23am UTC](https://mne.discourse.group/t/interpolate-bad-channels-before-or-after-car-referencing/3696 "2021-09-15T08:23:13Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@mscheltienne](https://mne.discourse.group/u/mscheltienne)
#### Post date: [September 15, 2021, 8:23am UTC](https://mne.discourse.group/t/interpolate-bad-channels-before-or-after-car-referencing/3696/1 "2021-09-15T08:23:13Z")
What is considered best practice?
Option 1:
1. Mark bad channels in `raw.info['bads']`
2. Interpolate bad channels with `raw.interpolate_bads(reset_bads=True, mode='accurate')`
3. Compute CAR reference as projector with `raw.set_eeg_reference(ref_channels="average", ch_type="eeg", projection=True)`
Option 2:
1. Mark bad channels in `raw.info['bads']`
2. Compute CAR reference as projector with `raw.set_eeg_reference(ref_channels="average", ch_type="eeg", projection=True)`, excluding the marked bads.
3. Interpolate bad channels with `raw.interpolate_bads(reset_bads=True, mode='accurate')` after applying the CAR projection.
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### Author:  [@cbrnr](https://mne.discourse.group/u/cbrnr)
#### Post date: [September 15, 2021, 11:08am UTC](https://mne.discourse.group/t/interpolate-bad-channels-before-or-after-car-referencing/3696/2 "2021-09-15T11:08:01Z")
I don’t think there should be a huge difference between these approaches. Setting an average reference ignores bad channels, so whether or not you interpolate them before or after should not matter much. FWIW I personally use the second approach (mark bads, set average reference, interpolate bads), but I’d be interested if you have found these two options to give significant differences.