We have dozens of customers worldwide for our software packages, and each package is highly customised for each customer's business. The severity measure lets us compare release quality across customers using an objective measurement defined and managed by us. The priority measure lets us refine that comparison per customised packaged. Generally, a release with a lot of high-severity issues will have a lot of high-priority issues (since by a default an S1 is a P1, an S2 is a P2, etc.), but some customers have different requirements, different custom features, and some are just more fussy.
If a base release that was customised for multiple customers has an expected number of P1, P2, P3, P4 issues for most customers but a high number of P1 and P2 issues for one particular customer, off of the same number of issues in the base release as measured by severity, then that will stand out in our measurements and we'll dive deeper into that customisation to see what's going on.
(Edited mid-stream... accidentally submitted too early.)
