Here's a sample size calculator tool: http://www.cardinalpath.com/tools/sample-size-calculator-tool/ http://www.cardinalpath.com/tools/sample-size-calculator-to

Here's a sample size calculator tool: http://www.cardinalpath.com/tools/sample-size-calculator-tool/ http://www.cardinalpath.com/tools/sample-size-calculator-too... And here's a post that addresses this issue: http://37signals.com/svn/posts/3004-ab-testing-tech-note-determining-sample-size http://37signals.com/svn/posts/3004-ab-testing-tech-note-det...