Click through rate: Except for high purchase intent searches, users will click on paid search listings at a lower rate than organic search listings. Organic listings have more credibility with search engine users. In one UK study, published by Econsultancy, only 6% of clicks were the result of paid listings. In another study, it was 10%. The important thing to remember is that click through rate varies by purchase intent. Organic rankings will get more click through rates for “top of funnel” keyword search queries.
Website saturation and popularity, or how much presence a website has on search engines, can be analyzed through the number of pages of the site that are indexed by search engines (saturation) and how many backlinks the site has (popularity). It requires pages to contain keywords people are looking for and ensure that they rank high enough in search engine rankings. Most search engines include some form of link popularity in their ranking algorithms. The following are major tools measuring various aspects of saturation and link popularity: Link Popularity, Top 10 Google Analysis, and Marketleap's Link Popularity and Search Engine Saturation.
Remember when you used to rely solely on search engines for traffic? Remember when you worked on SEO and lived and died by your placement in Google? Were you #1? Assured success. Well, okay, maybe not assured. Success only came if the keywords were relevant to your site users, but it was the only real roadmap to generating site traffic and revenue.