It would be beneficial to show the number of available data sets when correlating metrics. The reason for the request is that you can determine if the correlation is going to work based on the number of solutions, rather than correlating metrics only to find out that the correlation doesn't produce any results. The same could be done by showing a line item displaying a line item of correlated data. For example, if Prop 1 and Prop 2 are correlated, the following could be displayed:
Prop 1 & Prop 2 correlation display an estimate 300,000 line items
Sample: widget > home app
By displaying a single line item and the estimated number of available line items could provide some quick insight into the availability of a correlation before creating a correlation that may/may not work.