Usability Goals and Measures in Human-Computer Interaction

Standardization, Integration, and Consistency

To reduce the cognitive load on users, designers leverage established patterns:

• Standardization: Using pre-existing industry standards (such as W3C or ISO) helps users apply existing knowledge to new interfaces, thereby reducing errors.
• Integration: A product should be able to function seamlessly across different software tools and packages.
• Consistency: This involves maintaining compatibility across different versions of a product, ensuring it works with related non-computer systems (like paper forms), and using common action sequences, terms, colors, and units within the program.
• Portability: Users should be able to convert their data easily across various software and hardware environments.

Measuring Usability: The Five Human Factors

Once a design is implemented, how do we know if it actually works? Designers use five central human factors to evaluate the interface within a specific user community.

1. Time to Learn: How long does it take for a typical member of the target community to learn how to perform relevant tasks?
2. Speed of Performance: Once learned, how quickly can the user complete specific benchmark tasks?
3. Rate of Errors: How many errors do users make during benchmark tasks, and what types of errors are they?
4. Retention Over Time: How easily can users return to the system after a period of non-use? High ease of learning typically leads to better retention.
5. Subjective Satisfaction: This is measured through qualitative feedback, such as interviews, free-form comments, and standardized satisfaction scales.

Exam Tip: When asked to differentiate between "Speed of Performance" and "Time to Learn," remember that Time to Learn focuses on the initial acquisition of skill, while Speed of Performance focuses on the efficiency of an experienced user.

Design Iteration: Mockups and Prototypes

Design is rarely a linear process. Designers frequently face trade-offs; for example, updating an interface to add new functionality might inadvertently break consistency with a previous version.

To navigate these trade-offs, designers use two primary tools for evaluation:

• Mockups: These are often lower-fidelity representations used to test layout and flow early in the process.
• High-Fidelity Prototypes: These are more authentic, functional versions of the interface that allow for more realistic testing.

The fundamental trade-off in the design process is between the cost of feedback and the authenticity of the interface. Getting feedback early via mockups is inexpensive, whereas testing high-fidelity prototypes provides much more accurate data about how a user will actually behave.

Contextual Motivations

The importance of specific usability goals changes depending on the application domain:

By understanding these diverse motivations, designers can prioritize the right goals for their specific target audience.