📏 Usability Specifications §

= quantitative 🤲 Usability goals against which user 👉 Interaction Design is measured

Defined by: §

• Usability attribute
• Measurement value
• Target level of measurement value
• 👤 User subset
• Pre-conditions

Pros & Cons §

• 👍 Provides a concrete definition of 🤲 Usability, metrics and goals
• 👎 Usability is not easy to measure
  • high chance of 😊 Systematic measurement error (bias)
  • high cost

📖 Example: §

Efficiency (= usability attribute) of first time use measured by retrieval time of specified Information (= measurement value):

’90 % of student users (= user subset) without any prior training (= pre-conditions) should be able to retrieve the shelf number of a book, given the author and the title within 10 times the length of time an expert user (= target level) would take to complete the same task’