7.4 Science Fair Case Study: Usability Evaluation

Evaluation is central and continuous in SBD. From the first step of activity design, the use context provided by the scenarios serves as an implicit test of theemerging design ideas. The "what-if" reasoning used in analyzing claims expands and generalizes the situations that are envisioned and considered. The focus on design feature impacts is an ongoing source of formative evaluation feedback.

Evaluation becomes more systematic when usability specifications are created from design scenarios and their associated claims (Figure 7.4). The scenarios provide the motivation and activity context for a set of sequential subtasks that will be evaluated repeatedly as benchmarks of the system's usability. The claims analyses are used to identify the subtasks to be tested recall that claims have been used throughout to track design features with important usability implications. For each subtask, outcome measures of users' performance and satisfaction are defined, creating a testable set of usability specifications (Carroll & Rosson 1985).

Figure 7.4: Developing usability specifications for formative evaluation.

The high-level goal of any usability evaluation is to determine to what extent a design is easy or hard to learn and use, and is more or less satisfying. Usability specifications make this high-level goal more precise, transforming it into a set of empirically testable questions. The repeated testing of these tasks ascertains whether the project is meeting its usability goals, and if not, which design features are most in need of attention.