Why does the graph button of StatMate launch Prism version 4 instead of a newer version.

When you click the Graph button in StatMate, it will launch Prism to create the graph. 

If Prism 4 Windows is installed, then StatMate will always launch it -- even if Prism 5 and/or 6 are on your computer.  If you uninstall Prism 4, then StatMate will launch the last version of Prism you ran.