Finding usability problems is only half the work of a heuristic evaluation. Once you have a list of heuristic violations, someone has to decide which ones get fixed first, because development teams rarely have time to address everything. Severity ratings are the tool evaluators use to communicate how much each problem matters, turning a long, flat list of issues into a prioritized set of recommendations.
Nielsen's severity scale runs from 0 (not a usability problem at all) to 4 (usability catastrophe that must be fixed before release), with cosmetic, minor, and major problems in between. The rating you assign is a judgment call, but it is not arbitrary: it is based on how frequently users will encounter the problem, how much trouble it causes them when they do, and whether users can learn to work around it or are blocked by it every time. Because judgment varies between people, evaluations usually combine ratings from several evaluators and record each issue with its heuristic, its severity, and a suggested fix.
As you watch these videos, pay attention to the criteria the speakers use to justify a rating rather than just the numbers themselves. Notice how severity is described in terms of user impact, and think about how you would document a rating so that a teammate reading your report could understand why you chose it. This habit of recording and defending ratings is exactly what you will be asked to do in your own evaluation assignments.
A short, focused video from Nielsen Norman Group on assigning severity ratings to design issues found in usability studies or heuristic evaluations. It discusses the small set of criteria evaluators use to judge how serious a problem is, such as how often users hit it and how much it impedes them, and how those criteria translate into prioritized findings in a report.
This is the most directly on-topic video for the subtopics: it comes from the organization that defined the severity scale and it addresses purpose, criteria, and prioritization in just three minutes.
An overview of how to run a heuristic evaluation systematically: reviewing an interface against a set of heuristics, identifying potential usability and experience problems, and documenting what you find. Severity rating fits in as the step that follows identification, so this video supplies the surrounding process in which ratings are assigned and recorded.
It places severity rating in context by showing the full evaluation workflow, which helps you understand when and why ratings get assigned rather than treating the scale in isolation.
An explanation of the System Usability Scale, a standard ten-question survey given at the end of a usability test that produces a single score for perceived usability. It covers how the questionnaire works and how the resulting score is interpreted as a measure of overall usability.
It offers a useful contrast: SUS measures perceived usability of a whole system from users, while severity ratings are expert judgments about individual problems, and seeing both clarifies what severity ratings are and are not.
Together these videos move you from identifying problems to prioritizing them. The heuristic evaluation walkthrough reinforces MO1 and MO2 by showing how an interface is reviewed against heuristics and how violations are captured and classified. The severity video directly supports MO3, giving you the criteria and vocabulary to rate each violation and to justify that rating when you recommend specific design improvements. The SUS video rounds out your understanding of usability measurement, helping you distinguish an overall perceived-usability score from the issue-level severity judgments you will produce in this module.
These videos were chosen from YouTube on October 3, 2026. Each has captions; the player turns them on. Videos on YouTube can be changed or removed — if one no longer plays, tell your instructor. If a player does not appear, use its Watch on YouTube link.