Usability Engineering: Understanding and Evaluating User Interfaces

Posted on May 1, 2024 in Computers

Usability Engineering

Usability engineering involves systematic methods and theories for creating usable interfaces. It encompasses a process, checklists, and draws upon research in psychology and practitioner experience.

Understanding Users and Work

Several methods help understand user needs and work practices:

  • Interviews, Surveys, Focus Groups: Directly ask people about their wants and needs. While beneficial for user involvement, limitations include memory biases and social desirability effects.
  • Contextual Inquiry: Observe people in their actual work environment to gain insights into real behavior and contexts. However, observer effects and intrusiveness need consideration.

Properties of Good Concrete Tasks (Benchmark Tests)

Effective benchmark tests should be:

  • Concrete and Relevant: Clearly defined and directly related to user goals.
  • Comprehensive: Covering a range of user scenarios and functionalities.
  • Appropriate Difficulty: Challenging enough to assess usability without being frustrating.
  • Respectful and Unbiased: Avoiding leading questions or offensive content.

Think-Aloud Protocol

Think-aloud is a valuable technique where users verbalize their thoughts while interacting with an interface. This provides insights into their mental models, problem-solving strategies, and frustrations. It is inexpensive, works well with early prototypes, and can be conducted by inexperienced evaluators.

Stages of Running an Evaluation

  1. Preparation
  2. Introduction
  3. The Test
  4. Questionnaire/Interview
  5. Debriefing
  6. Analysis

Recruiting Participants

Consider the representativeness of participants and the impact of user population on conclusions. Iterative testing with different user groups is often beneficial.

Data Collection

Collect data through observation (direct/indirect, notes, video/audio recordings), software logs, and questionnaires with open-ended and closed-ended questions.

Pros and Cons of Thinking Aloud

Pros:

  • Identifies usability problems and their causes.
  • Requires a small number of participants.
  • Cost-effective and usable early in development.
  • Requires minimal facilitator expertise.
  • Generates insightful user quotes.

Cons:

  • Thinking aloud can slow users down and alter their behavior.
  • Does not provide performance data.
  • User’s “theories” require careful interpretation.

Heuristic Evaluation

Heuristic evaluation involves experts reviewing an interface against established usability heuristics (e.g., Nielsen’s heuristics) to identify potential problems.

Main Stages of Heuristic Evaluation

  1. Preliminaries: Define heuristics, tasks, and prototype.
  2. Evaluation: Experts independently assess the UI and record violations.
  3. Concluding Summary: Summarize and rate flaws based on severity, frequency, impact, and persistence.

Advantages and Problems

Heuristic evaluation is efficient and does not require user studies. However, it relies on finding qualified evaluators and may identify issues that do not affect real users or miss actual problems.

Evaluation Approaches

Evaluation approaches can vary in rigor and speed:

  • Rigorous: Maximize effectiveness and minimize risk, often involving lab and field studies.
  • Rapid: Prioritize speed and cost-effectiveness, suitable when initial tests reveal significant issues.
  • Empirical: Involve users directly, such as think-aloud protocols.
  • Analytic: Rely on expert analysis, such as heuristic evaluation.

Data can be quantitative (e.g., task completion rates) or qualitative (e.g., user comments).

Risks to Validity

Consider potential risks to the validity of think-aloud and heuristic evaluations:

  • Participant Representativeness: Ensure participants accurately represent the target user population.
  • Task Selection: Choose tasks that are relevant and cover the essential functionalities.

Guidelines and User Experience

Usability guidelines can be helpful but require careful interpretation and application. They do not guarantee a good user experience and should be complemented with comprehensive UX evaluation.

Writing User-Friendly Content

To enhance usability, consider these writing principles:

  • Use familiar language.
  • Chunk content into manageable sections.
  • Prioritize important information.
  • Use pronouns and active voice.
  • Keep sentences and paragraphs concise.
  • Utilize bullets, lists, and clear headings.
  • Incorporate visuals and multimedia.
  • Maintain white space for readability.

Ben Shneiderman’s Golden Rules for Dialogue Design

These principles promote effective interface dialogues:

  • Consistency
  • Shortcuts
  • Informative feedback
  • Closure in dialogues
  • Simple error handling
  • Easy reversal of actions
  • Support internal locus of control
  • Reduce short-term memory load

Mental Models and User Models

Mental models represent people’s beliefs about a system, influencing their interactions. Mismatches between user and designer mental models are common. User models are representations of users’ mental models.

Key Interface Terms

  • Affordances: Perceived functionalities of an interface based on the user’s mental model.
  • User’s Goals: Design should focus on supporting user goals and avoid extraneous information.
  • Information Scent: Users selectively attend to information relevant to their current goals.
  • Gulf of Execution and Evaluation: The cognitive effort required to interact with and interpret an interface.

By understanding usability principles and evaluation methods, designers can create interfaces that are effective, efficient, and enjoyable for users.