Displayed as one to five bars, the quality index is a relative measure of your ad’s performance. It tells you how well your ad is performing, on average, for all of the keywords for which it is displayed, relative to other ads it was displayed with. It reflects your ad's ability to meet the needs of users by looking at your click-through rate, as well as other relevancy factors. Your ad's quality index also impacts how much you need to bid to achieve your desired position – ads with a higher quality index require a lower bid and/or receive better placement on the results page.wer bid and/or receive better placement on the results page.