<p>
            As we can see in the graph: embedding external content has seen a usage increase in popular websites today. We have found a significant increase of more than five fold of external requests. In the year 2015 we found an average of around 6 external requests per website. This means at least 6 other hosts were informed about each visit of a website. The most used external hosts could be connected to web tracking.
            </p>

            <p>
            An important question is how many trackers cover how many popular websites' users and can thus track a large number of users. We analyzed how many of all websites are covered by the top N (1-50) trackers. In 2015 about 73% of all analyzed websites are covered by the top three of the most included third party trackers from 2015. In 2005, only 10 % of the websites are covered by the top three from 2005.
            </p>

            <p>
            This kind of analysis could also be interesting if domains of a specific company are grouped together. For example, to analyze the coverage of Google-hosts. For this analysis they are simply identified by "google" in their hostname -- other services that are today (as of 2015) part of the google company (like doubleclick.net since 2007 or youtube.com since 2006) are not considered. The results for this analysis are that in the year 2005 only 5 % of the websites were covered by Google. This figure rapidly increased for the following years (2006-2015): 19 %, 36 %, 49 %, 57 %, 65 %, 72 %, 78 %, 80 %, 81 %, 82 %. This means that Google increased their coverage from 5 % to 82 % in the last 10 years.
            </p>