Custom variables are name-value pair tags that you can insert in your tracking code in order to refine Google Analytics tracking.
https://developers.google.com/analytics/devguides/collection/gajs/gaTrackingCustomVariables?hl=en
Analytics and Tracking
Get access to data on 31,764 websites that are Google Analytics Custom Variables Customers. We know of 8,750 live websites using Google Analytics Custom Variables and an additional 23,014 sites that used Google Analytics Custom Variables historically and 3,772 websites in the United States.
Get a list of 31,764 websites using Google Analytics Custom Variables which includes location information, hosting data, contact details, 8,750 currently live websites and an additional 69,189 domains that redirect to sites in this list. 23,014 sites that used this technology previouslyand 3,772 websites in the United States currently using Google Analytics Custom Variables.
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