Stats calculator for Google Analytics

[Update 03/05/2012: Added support for the new Google Analytics UI]

[Update 11/03/2011: We have since added goal conversion rates as well. However, please note that it uses the overall goal conversion rate, which is the sum of all goals. Use appropriately]

Can you be sure that a conversion rate of 5.56% is better than 4.87% if you only have a few data points? It’s important to think statistically when working with this kind of data.

I wanted to share a Z-Test calculator that you can use directly in Google Analytics via a simple bookmarklet. It uses the jstat library. You’ll need to use the new version of Google Analytics and have e-commerce tracking enabled as it works on the e-commerce conversion rate.

Please drag the button below to your bookmarks bar (you’ll need to be viewing the post on my site directly, not in an RSS reader):

Z-Test

And then click on it in any report that has Plot Rows checkboxes and select the e-commerce tab. Or take a look at the 2 minute video:

(You may want to watch a larger version directly on youtube)

A couple of notes. I decided to show the confidence interval so that you can decide if you want to use a 95% confidence level. Hat tip to my friend Kevin Potcner for giving me feedback on this.

Doing a statistical analysis on observational data will perhaps not give you quite as strong a signal as from a controlled experiment, but it’s still a valid approach. Try to isolate the question you are trying to answer by segmenting your data.

Have fun!

Michael

P.S. I tested it in Chrome and FF on a Mac, but if it doesn’t work somewhere else I am sorry. It’s just a tool we built for ourselves, which we are now sharing in the hope that it may be useful for other folks. Feedback is of course appreciated!

If you want to give me feedback on this post, please contact me.