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Standard Metrics Revisited: #1: Visitors - Occam's Razor by Avinash Kaushik
Analytics Basics: Unique Visitors, New vs. Returning Visitors | ClickZ
Analytics Basics: Averages and Ratios | ClickZ
Web Metrics: Average Session Length vs Repeat Visitor Ratio | Inc.com
How To Analyse New And Returning Visits In Google Analytics