Defect severities, part 1 - Severity versus Priority

Summary
Severity is technical, priority is political

Severity is about the technical impact of a defect. Priority is about the urgency of the fix. Important is that severity is one of the factors influencing priority and that only priority should be used to decide what to fix next. An example severity might be:

1. Critical – damn thing doesn’t run or loses data
2. High – important feature doesn’t work
3. Medium – minor feature doesn’t work
4. Low – nobody would care anyway

Sample priorities

1. Fix now (before next build)
2. Fix soon (before next release)
3. Fix sometime (whenever)

Customers tend to assign very high severity to all defects. I think this is because they are trying to influence priority through severity. Further reading:

• StickyMinds.com: Arguing Apples and Oranges. I like “The ultimate lesson here, regardless of the terms or levels you use to categorize your bugs, is that any classification scheme will only be effective if everyone agrees on definitions”
• Bug Triage Meeting—Severity & Priority
• Here’s a different view: Clarify Your Ranking for System Problem Reports. I don’t agree. Very much for this reason