Average of an Average of an Average

Hello,

I have a project that is using an interesting methodology to score social media ads/campaigns/accounts. They first score each ad, then they average the ad level scores to get the campaign score, then they average the campaign scores to get the account scores.

In the example above I score the ad based on the impressions:

case when impressions < 20 then 1

when impressions < 40 then 2

when impressions < 60 then 3

when impressions < 90 then 4 else 5 end

This gives me my ad level score. Then I need to average the ad scores to get the campaign score, and average the campaign score to get the account score.

I would also need to use the above to create cards that are rolled up at the campaign and account level:

Please help!