One very useful feature of Google Analytics is the comparison of time-frames for a given metric. We can compare number of sessions, bounce rate, E-commerce transactions, AdWords cost, etc. between adjacent weeks, months, or years.
One shortcoming in this comparison feature, is that the percentage change calculated by Google for these metrics is not qualified. This extension addresses this shortcoming by providing a one-click evaluation of the current time-frame in your Google Analytics. You can use this tool for evaluating almost any graphable metric in Google Analytics.
Currently, for 5 < points < 40 the Wilcoxon Signed-Rank test is used. For points > 40, the paired Student's t-test is used.
1. Time frames to be compared must begin on the same weekday (Monday and Monday or Friday and Friday). They should be the same length of time. Be careful to ensure this, especially for year-over-year monthly comparisons. This script derives its statistical power by treating metrics as paired data points (based on the day of the week).
2. Must compare at least 5 data points (days, weeks, or months). Beyond the lower limit, the statistical test lacks sufficient power.
For further documentation and description of the statistical tests, visit the support article on the LunaMetrics blog: http://www.lunametrics.com/blog/2014/03/27/statistical-significance-script-google-analytics/