By the end of this lesson you can
- Rate usability issues consistently by severity.
- Combine severity with frequency and effort to prioritise.
- Agree priorities with your team.
The idea
Tests produce many issues. Not all are equally important. Severity describes how much an issue harms users.
A simple scale
- Critical: prevents people completing a task, or causes harm such as data loss or wrong payments.
- Serious: causes significant delay, frustration or errors, but people can recover.
- Minor: causes small hesitation or annoyance.
- Cosmetic: noticeable but does not affect task success.
Factors
Consider impact (how badly it affects people), frequency (how many people hit it) and persistence (does it happen once or every time?). An issue that affects one participant but blocks payment may outrank one that slightly annoys everyone.
Prioritising fixes
Combine severity with the effort to fix. Quick fixes to serious problems come first. Plot issues on a matrix of severity against effort and discuss with product and engineering partners.
Why it matters in real projects
Without prioritisation, teams either try to fix everything (and ship nothing) or fix the easiest cosmetic issues and leave serious ones. Clear severity ratings help the team agree what matters, and they make research findings actionable.
A realistic example
A test of a ticket booking site produces 23 issues. The team rates them: two critical (a seat selection error that books the wrong seats, and a payment page that fails on one browser), six serious, ten minor and five cosmetic.
On a severity-effort matrix, the browser payment bug is critical and quick to fix, so it goes into the current sprint. The seat selection redesign is critical but larger and is scheduled next. Cosmetic issues go into the backlog.
Step by step
List issues
Gather all issues from sessions.
Define the scale
Agree severity definitions with the team.
Rate independently
Have two people rate each issue, then discuss differences.
Add frequency
Note how many participants hit each issue.
Estimate effort
Ask engineers for rough effort.
Plot and agree
Plot severity against effort and agree priorities.
Common mistakes
Mistake Rating by personal annoyance.
Instead Use agreed definitions focused on user impact.
Mistake Counting frequency only.
Instead Weigh impact; rare critical issues matter.
Mistake Prioritising without engineers.
Instead Include effort estimates from the team.
Check your understanding
Choose an answer, then check it. There is an explanation either way.
Practice exercise
Exercise · about 45 min
Prioritise findings
Prioritise a list of usability issues.
Steps
- Use issues from your heuristic review or a test.
- Rate severity with a partner.
- Estimate effort.
- Plot a matrix and write the top five priorities.
Deliverable
A rated issue list, matrix and priorities.
Self-assessment
Tick each item when it is true of your exercise. Be honest; this is for you.
4 items
Summary
- Severity measures harm to users.
- Consider impact, frequency and persistence.
- Combine with effort to prioritise.
- Agree priorities together.
Further reading
Third-party sources, chosen for reliability. They open in a new tab.
Your notes
Marking complete updates your course and roadmap progress.