AB split test graphical Bayesian calculator

This calculator tells you, given the split test data you have, how likely is it that one version is better than another.
A Bayesian approach avoids many of the issues with z tests and G tests, and can often enable you to draw meaningful conclusions, even where conversion rates and sample sizes are low.
The probabilities calculated go directly to the business question of which version is best.

Visit durations normally distributed? Not likely.

Time on site is an incredibly useful metric, but fraught with difficulties of collection and interpretation. For example Google’s presentation in the behaviour/engagement reports, at first glance, makes visit duration look normally distributed, but they aren’t.
Using the analytics API in a spreadsheet enables a much closer look at the distribution of visit lengths.

Pull Google Analytics data into a Google Docs spreadsheet using the API

Update: a better solution

Google now presents an inbuilt library for accessing Google analytics from Google docs. You can see how to use it with a ready-made and powerful solution for template driven analytics reports and dashboards here.

This post is left here in case it is of interest to anyone. However, this is no longer the best way of accessing the Google Analytics API from Google Docs. Google have made an interface available directly within docs script, as described in the Google Analytics blog.

The Google Analytics Reporting API enables you to automate reporting tasks, combine GA data with other information, apply analysis and visualisation tools, and access data you couldn’t easily reach via the Google Analytics UI.

As well as reducing repetitive work, this reduces your chance of errors, and enables you to build up more sophisticated analysis.