

A/B test duration calculator (with resources) - paraschopra
http://visualwebsiteoptimizer.com/split-testing-blog/ab-test-duration-calculator/

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hnsmurf
There are a ton of web based ones if you don't want to use a spreadsheet.
These calculators are very popular amongst direct marketing and CPA affiliate
profiteers. I hesitate to link to any here for fear of being marked a spammer,
but a Google search will turn up tons.

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randall
Providing links in HN isn't seen as spam, especially if it clears up a missing
point. I, for one, would appreciate any links you've got of ones you trust and
use.

