Usability Evaluation.ppt

SBD:Usability Evaluation Chris North CS 3724: HCI Evaluation Formative vs. Summative Analytic vs. Empirical Usability Engineering Usability Engineering Usability Evaluation Analytic Methods: Usability inspection, Expert review Heuristic: Nielsen’s 10 Cognitive walk-through GOMS analysis Empirical Methods: Usability Testing Field or lab Observation, problem identification Controlled Experiment Formal controlled scientific experiment Comparisons, statistical analysis User Interface Metrics Ease of learning Ease of use User satisfaction User Interface Metrics Ease of learning learning time, … Ease of use performance time, error rates… User satisfaction surveys… Not “user friendly” Usability Testing Usability Testing Formative: helps guide design Early in design process when architecture is finalized, then its too late! Small # of users Usability problems, incidents Qualitative feedback from users Quantitative usability specification Usability Specification Table Usability Test Setup Set of benchmark tasks Derived from scenarios (Reqs analysis phase) Derived from claims analysis (Design phase) Easy to hard, specific to open-ended Coverage of different UI features E.g. “Find the 5 most expensive houses for sale” Different types: learnability vs. performance Consent forms Not needed unless recording user’s face/voice (new rule) Experimenters: Facilitator: instructs user Observers: take notes, collect data, video tape screen Executor: run the prototype for faked parts Users Solicit from target user community (Reqs analysis) 3-5 users, quality not quantity Usability Test Procedure Goal: mimic real life Do not cheat by helping them complete tasks Initial instructions “We are evaluating the system, not you.” Repeat: Give user next benchmark task Ask user to “think aloud” Observe, note mistakes and problems Avoid interfering, hint only if completely stuck Interview Verbal feedback Questionnaire ~1 hour / user Usability Lab E.g. McBryde 102