Subjects

Usability Testing and Evaluation

Covers moderated vs. unmoderated usability testing and the factors that decide between them, heuristic evaluation against Nielsen's 10 heuristics as a complement to (not replacement for) real user testing, the completion-rate/time-on-task/error-rate triad and why you need all three together, the System Usability Scale's exact 10-item structure and 0-100 scoring formula with Bangor/Kortum/Miller benchmarks, the think-aloud protocol and its common facilitation pitfalls, when A/B testing is the right tool versus when usability testing is, and the recruiting/sample-size/confirmation biases that undermine a study's findings.

Interaction Design Principles

Covers Nielsen's 10 usability heuristics with concrete UI examples, the Gestalt principles of perceptual grouping (proximity, similarity, common region, closure, continuity), Fitts's Law and target sizing, Hick's Law and choice overload, Don Norman's affordance/signifier distinction and the flat-design failure mode, feedback loops and the 'dead click' problem, and the error-prevention-over-error-recovery hierarchy.

Accessibility and Inclusive Design

Covers the WCAG POUR principles (Perceivable, Operable, Understandable, Robust) with a concrete example of each, the A/AA/AAA conformance levels and why AA is the real-world target, exact WCAG 2.1 AA contrast ratios (4.5:1 normal text, 3:1 large text and UI components), keyboard navigation and visible focus indicators, how screen readers build the accessibility tree from semantic HTML and ARIA, ARIA landmarks and labels, the Microsoft Inclusive Design framework's permanent/temporary/situational model, and a worked 'make this dropdown accessible' interview walkthrough.