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

Siddharth Shah on October 9, 2009 at 7:00 am

A question often posed by marketers is, “What is the relative importance of different factors Google uses to determine quality score (QS)?”. Some of the factors mentioned on the AdWords blog are:

Click through rate of the keyword and the matched ad
Account history
Landing page quality
Keyword/Ad Group relevance

The question for an advertiser then becomes, “What factor should be the primary focus when trying to improve my quality score?.” The answer is overwhelmingly the click through rate (CTR).

For the analysis, we looked at several Google accounts and plotted quality score vs. CTR. A typical plot for a large account with 500,000+ keywords looked like this:

Several interesting patterns show up:

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.
There is a sudden jump at a quality score of 8.
While CTR does not explain the jump between 9 and 10, there is a huge jump in CTR between 8 and the higher quality scores.

But there is more to it. Some quality scores appear more frequently than the others. We found in our analysis of millions of keywords that quality scores of 8 and 9 are very rare. Here is a typical example for a Google account. It appears that the quality scores of 8 and 9 are “transition” regions. While a linear trend explains the QS-CTR connection until the score of 7, keywords with QS of 9 and 10 require a very high quality score compare to the rest.

Percentage of Keywords vs. Quality Score

We found this pattern across the board, in all verticals.

The takeaway is that when looking to improve quality score, first seek to improve your CTRs. This will have the biggest impact, by far. Do not worry if you see very few keywords at a quality score of 8 or 9. These scores are rare and do not appear to have a direct connection with CTR related factors. There is not much you can do to get these scores. In fact, it likely has something to do with the way Google’s Quality Score algorithm works. Once you have the CTR piece of puzzle solved, work on the other factors (such as landing page quality, ad copy relevance and campaign structure) to improve your quality score. And don’t waste your time fretting about getting the highest score.

Opinions expressed in this article are those of the guest author and not necessarily Search Engine Land. Staff authors are listed here.

About The Author

Siddharth Shah

Siddharth Shah is head of web analytics, digital strategy and insights at Adobe. He leads a global team that manages the performance of over $2 BN dollars of ad spend on search, social and display media at Adobe.