user has seen, for example the URL of the page. Google analytics JavaScript libraries uses HTTP cookies, with which it remembers what a user has done on previous pages and his interactions. Another limitation of Google Analytics for large websites is the use of sampling in the generation of many of its reports. To reduce the load on their servers and to provide users with a relatively quick response to their query, Google Analytics limits reports to 500,000 randomly sampled sessions at the profile level for its calculations. While margins of error are indicated for the visits metric, margins of error are not provided for any other metrics in the Google Analytics reports. For small segments of data, the margin of error can be very large. One of the biggest limitation of Google Analytics, is its inability to track and attribute offline conversions. Offline conversion tracking is required to measure the impact of online marketing campaigns in "offline" environments, such as Point of Sale, Call Centers, Affiliate Networks, or payment gateways. Since Google Analytics is a JavaScript tag set on a website, when the visitor switch from the website environment to a phone conversation, the tracking is lost, and the "call center" activity can't be directly linked to the initial visit or visitor. Third-party tools integrated with Google Analytics, are now capable of tracking customer journey from online to offline environments. Performance There have been several online discussions about the impact of Google Analytics on site performance. However, Google introduced asynchronous JavaScript code in December 2009 to reduce the risk of slowing the loading of pages tagged with the ga.js script. Privacy Due to its ubiquity, Google Analytics raises some privacy concerns. Whenever someone visits a website that uses Google Analytics, Google tracks that visit via the users' IP address in order to determine the user's approximate geographic location. To meet German legal requirements, Google Analytics can anonymize the IP address. Google has also released a browser plug-in that turns off data about a page visit being sent to Google, however, this browser extension is not available for mobile browsers. Since this plug-in is produced and distributed by Google itself, it has met much discussion and criticism. Furthermore, the realization of Google scripts tracking user behavior has spawned the production of multiple, often open-source, browser plug-ins to reject tracking cookies. These plug-ins allow users to block Google Analytics and similar