usability-testinglisted

# Usability Testing ## Coverage Usability testing covers the evaluative research practice of watching people attempt realistic tasks on a prototype or product, then identifying the obstacles they encounter. The dominant method is the **think-aloud protocol** (Ericsson & Simon), where participants narrate their thoughts as they work, surfacing the mental model they are using and the points where it diverges from the design. Sessions are organized around **task scenarios** — short narratives that frame a goal without prescribing the steps ("you want to find out how much you owe in taxes this quarter") — and a **moderator** who maintains neutrality, resists answering questions, and prompts only with open-ended interventions like "what are you thinking now?" or "what did you expect to happen?". The skill covers **sample sizing**. The widely-cited Nielsen/Landauer "5-user rule" estimates that 5 users surface ~85% of major usability problems for a homogeneous user group on a discrete task, with steeply diminishing returns afterward. The rule has important limits: it applies per distinct user segment, per discrete task scope, and to **formative** (iterative diagnostic) testing — not to **summative** (benchmark) studies, which require much larger samples for valid statistical comparison. Misapplying the 5-user rule to summative claims is a common error. Findings are organized by **severity rating** (Nielsen's 0–4 scale: cosmetic, minor, major, catastrophic) so the team can triage.