How to exclude holidays from a report showing a weekly / daily average volume of incidents

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I have a report which shows the average number of incidents per day. I need a way to write the daily average column so that it excludes days which are configured as holidays. 

Currently, this is my column definition:

sum(stats.new_incidents) / 5

Any recommendations on how to write this so that the holidays in our configuration are excluded from this calculation? Thanks!