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How important Is Click Through Rate In Google’s Quality Score Formula?

Quality scores from 1 to 8 are very well explained by CTR. Notice how the linear regression (line fit) aligns so well with the observed pattern. The R squared of 72% of the trend is explained by CTR alone.

We found in our analysis of millions of keywords ...

The takeaway is that when looking to improve quality score, first seek to improve your CTRs.