When the world is crashing around you, trust the data. Dive into Google Analytics and try to pinpoint where things went south. Think back on marketing tactics you recently pushed live and find the correlation. This should lead you to an internal audit, where you may discover an internal tool is broken or an external force is impacting your site. - Kirk Deis, Treehouse 51
Web analytics is the measurement of the behavior of visitors to a website. In a commercial context, it especially refers to the measurement of which aspects of the website work towards the business objectives of Internet marketing initiatives; for example, which landing pages encourage people to make a purchase. Notable vendors of web analytics software and services include Google Analytics, IBM Digital Analytics (formerly Coremetrics) and Adobe Omniture.