Abstract
This paper aims to understand how third-party ecosystems have developed in four different countries: UK, China, AU, US. We are interested in how wide a view a given third-party player may have, of an individual user's browsing history over a period of time, and of the collective browsing histories of a cohort of users in each of these countries. We study this by utilizing two complementary approaches: the first uses lists of the most popular websites per country, as determined by Alexa.com. The second approach is based on the real browsing histories of a cohort of users in these countries. Our larger continuous user data collection spans over a year. Some universal patterns are seen, such as more third parties on more popular websites, and a specialization among trackers, with some trackers present in some categories of websites but not others. However, our study reveals several unexpected country-specific patterns: China has a home-grown ecosystem of third-party operators in contrast with the UK, whose trackers are dominated by players hosted in the US. UK trackers are more location sensitive than Chinese trackers. One important consequence of these is that users in China are tracked lesser than users in the UK. Our unique access to the browsing patterns of a panel of users provides a realistic insight into third party exposure, and suggests that studies which rely solely on Alexa top ranked websites may be over estimating the power of third parties, since real users also access several niche interest sites with lesser numbers of many kinds of third parties, especially advertisers.