What is Google Analytics and why it is important?

Google Analytics (abbreviated GA) is a free service offered by Google that generates detailed statistics about the visitors to a website.

Accordingly to Google.com:

"Google Analytics shows you how people found your site, how they explored it, and how you can enhance their visitor experience. With this information, you can improve your website return on investment, increase conversions, and make more money on the web. This guide can help you familiarize yourself with the main features of Google Analytics."

Reference:

http://www.google.com/support/analytics/bin/answer.py?hl=en&answer=55591

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