Test Status with Lightweight charts - no Group by on Test Cases

I'm trying to create a Test Case chart with TFS 2013 Update 4.

I open my TFS project in a browser.

I select "Test" from the top menu.

I select one of my Test Plans

I select "Charts" from the right-hand side

I select "New"

I select "New test case chart"

I select "Group by"

Nothing appears

What should show up here and why doesn't it?

Bruce