For a group of workitems, is there a way to get the average of a decimal field with in a workitem and display that value on dashboard.

I am currently tracking customer satisfaction rating within the DPO workitem.  Each workitem represents a DPO project with a different customer.  I have written a query to produce a report with all closed workitems and display their corresponding customer sat rating.
Question:  I am wondering if there is a way to gather those customer sat ratings from multiple workitems, calculate the average and display the average customer sat rating for a group of workitems on my dashboard?
Thank you.