Statistics Tables help you see multiple aggregate metrics for your chosen data source. This visualization evaluates all of the responses collected for that data source and displays calculated results such as mean and standard deviation.
You can use a custom metric in the dashboard parameters and create a variable that will be used in the dashboard!

I am not sure that really helps me. Seems I need the calculation done in custom metrics in the dashboard settings so that it is dynamic as users select different filters (just like mean and count is dynamic). Ultimately what I want is to create a t-test for mean differences that I can show in a table. So actually I need SD and square root in the custom metrics. Seems pretty basic, but it seems I can't do that in dashboards. The stats are not for me for to use, but the users in my contact list who only see results for their group (restricted by field in roles) but who can see comparison results in gauge charts (using roll-up), or by selecting "All" on the field where I restricted data. There is an option for significance testing on some of the bar graphs, but it provides no real useful information to the user (not to mention the arrows used are very small and hard to see). Thanks for any assistance anyone can provide.