Back in August 2005, Google stopped ranking ads by the simple product of CTR times CPC and instead moved to ranking by Quality Score. Quality Score is highly correlated with CTR, but also has other intentionally undefined factors. To quote Google:
Quality Score: This is the basis for measuring the quality of your keyword and determining your minimum bid. Quality Score is determined by your keyword's clickthrough rate (CTR) on Google, relevance of your ad text, historical keyword performance on Google, the quality of your ad's landing page, and other relevancy factors.Since Quality Score isn't defined publicly, Google can (and should) tweak their paid search rankings freely, which there are reports they may be doing in their effort to combat content spam clickfraud. The result? CPCs forced higher on affiliate and MFA pages.
Good. Clearly subjective, and clearly good.
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