Google Analytics is a service offered by Google that generates detailed statistics about a website's traffic and traffic sources and measures conversions and sales. It's the most widely used website statistics service.
Google Analytics can track visitors from all referrers, including search engines and social networks, direct visits and referring sites. It also tracks display advertising, pay-per-click networks, email marketing, and digital collateral such as links within PDF documents.
Google Analytics' approach is to show high-level, dashboard-type data for the casual user, and more in-depth data further into the report set. Google Analytics analysis can identify poorly performing pages with techniques such as funnel visualization, where visitors came from referrers, how long they stayed and their geographical position. It also provides more advanced features, including custom visitor segmentation.
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 for their query, Google Analytics limits reports to 500,000 randomly sampled visits 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.