Effectiveness is measured by accuracy and completeness of task outcomes, not by completion rate alone

What it is

In the standard's sense, effectiveness has two components: accuracy (was it done right—error counts, error severity) and completeness (was it done fully—coverage of the goal state). Completion rate is only a coarse proxy for both: a "completion" can carry three errors and skip two required steps, and recording it as a 1 overstates accuracy and completeness at once.

Why it happens

The binary collapse of completion discards quality information, while real task demands are graded: an expense form submitted with a wrong amount, a report exported missing a section—both "completed." Accuracy and completeness are independent dimensions—one can be complete but inaccurate (everything done, two errors) or accurate but incomplete (everything done was right, but not everything). Their failure causes differ too: accuracy failures stem mostly from missing feedback and weak confirmation; completeness failures from broken flows and missing entries.

Studying it

Per the standard, define "accurate" and "complete" criteria first: accuracy via error counts and a classification code sheet, completeness via a goal-state checklist checked item by item. Report separately: error-free complete completions, the distribution of completed-with-errors, and abandonment points—not one completion rate. Automated logs cover completeness and timing, while error classification still needs human coding; together they meet traceability requirements.

Where it stops holding

Criteria carry subjectivity: "accurate" tolerance varies by task—financial tasks and creative writing differ—and the completeness checklist is researcher-constructed, so checklist bias flows straight into results. For exploratory tasks the "goal state" is fuzzy, weakening both operators. The framework assumes a determinate task endpoint and does not fit open-ended use.

Applying it

• Write accuracy and completeness criteria for every task—error types and tolerances, goal-state checklist items—into the test script.
• Present reports in separate layers: error-free complete rate, completed-with-errors distribution, and abandonment-point distribution.
• List "completed with errors" as its own problem class; it often exposes feedback defects better than non-completion does.

Related

• Same group: B5.09.2 Efficiency's denominator is a resource—time, steps, or cognitive effort—and the report must say which · B5.09.3 Satisfaction is a subjective judgment, correlated with performance but not inferable from it · B5.09.4 Gains on the three dimensions can offset each other; report them separately instead of merging into one score
• Nearby: B5.02 Three Components · Q2 Usability Testing
• Search terms: effectiveness measures · accuracy completeness · error classification