Quality Score is a Google measure of historical click-through rate (CTR) of the keyword and matched Ad, account history (CTR of all Ads and Keywords in your account), historical CTR of the display URLs in the Ad Group, Quality of Destination Page, relevance of keywords to Ads within Ad Group, relevance of keyword and matched Ad to search query, and account performance in geographical region. Quality Index is a Yahoo! measure of Bid or Click Price, Historical click-through data, Conversion data, Organic Rankings of Advertiser URL, keyword appears in Title, keyword in URL, Keywords on Destination Page, Other keywords at the Campaign level and a comparison between other sites competing on the same keywords.
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