Basis for measuring the quality of keywords and determining minimum PPC bids. This score is calculated by measuring a keyword’s click-through rate, ad text relevancy, the keyword’s historical performance and the quality of the landing page. Quality score is mainly used by Yahoo, Google and Bing, and it can control cost per click and rank of advertisement. There is a need for ads to be listed, and therefore a formula exists based on which this order occurs. The formula is: bid*Quality Score. When results are received, ads are listed based on it. None of the mentioned search engines have exposed the real weight of quality score against the bid. They have told that they have the right to change and adjust their methodologies because there is a constant change of products and the need for these products.
The major search engines have each independently implemented efforts to maintain and improve the quality of ads listed on their sites. The primary reason for this is to improve the experience of users who click on paid advertising links. It is reasonable to assume that users who have a great experience when clicking on ads will click on them more frequently, thus increasing advertising revenues for the search engine.