Named Prototyping Methods
The Prototyping Toolkit
Beyond the Lo-Fi/Hi-Fi distinction, the course covers several named prototyping methods. Each serves a different purpose and is appropriate at a different stage.
| Method | Description | Best for |
|---|---|---|
| Paper prototyping | Hand-drawn screens on paper or card. A human facilitator plays the role of the “computer,” swapping screens in response to user actions. | Earliest-stage concept testing. Fastest and cheapest method. Tests overall structure and navigation. |
| Wizard of Oz | A human secretly operates the “system” behind the scenes while the participant believes they are interacting with a real (often automated or AI) system. The participant’s actions are intercepted and the human generates plausible responses. | Testing interaction concepts before the underlying technology exists — e.g. testing a speech interface before the speech-recognition engine is built, or testing an AI recommendation system before the ML model is trained. |
| Wireframing | Low-detail digital layouts showing structural layout — where text, buttons, images, and navigation go — without colour, imagery, or precise typography. | Mid-stage structural validation. More shareable and consistent than paper sketches; still clearly not “finished.” |
| Hi-Fi digital mockup | High-detail static screens showing final look-and-feel (colour, typography, imagery, branding) but not necessarily interactive. | Stakeholder sign-off on visual design; detailed aesthetic evaluation. |
| Interactive prototype | Clickable prototype linking mockup screens to simulate navigation without real back-end logic. Tools like Figma, Adobe XD, or Sketch. | Usability testing of navigation flows; testing whether the user understands where to tap and what happens next. |
| Vertical prototype | Full, deep implementation of a small number of features — all layers (UI, business logic, database) are functional for those features. | Testing technical feasibility and depth. “Can we actually build the recommendation engine that powers this one feature?” |
| Horizontal prototype | Shallow implementation across all features — the UI for every screen exists, but the back-end logic is mocked or missing. | Testing breadth and overall user-journey coverage. “Does the flow from login through checkout make sense as a complete experience?” |
Wizard of Oz in Detail
Wizard of Oz prototyping deserves special attention because it is conceptually unusual and highly examinable (2018 Q6, 2021 Q5).
The user interacts with what they believe to be a functional system. Unknown to them, a human “wizard” is observing their actions and generating the system’s responses in real time — typing the response text, triggering the next screen, or speaking as the “voice assistant.” The wizard follows a script or protocol to ensure responses are consistent.
When Wizard of Oz is the right choice:
- The technology to genuinely implement the system does not yet exist (e.g. testing a gesture-recognition interface before the computer-vision pipeline is built).
- The cost of building a real prototype for a one-off test is prohibitive.
- You want to test the interaction concept (does this conversational flow feel natural?) before committing to the implementation concept (which ML model, which NLP pipeline).
Risks:
- The wizard may be inconsistent across participants, introducing confounding variables.
- The wizard’s response time may be slower or faster than the real system, distorting user perception.
- If the user discovers the deception, trust in the research process is damaged.
Exam Tip: Sketching a Design
When asked to sketch an app design in a Tripos answer:
- Draw 2–4 clearly labelled screens, with captions describing interactive elements (what happens when the user taps each).
- Explicitly connect each screen back to a requirement you stated earlier in your answer: “the Resume Builder screen satisfies Requirement 2: users must be able to edit their CV offline.”
- Marks are awarded for labelling and justification, not artistic quality. A rough but clearly annotated sketch scores higher than a beautiful but unexplained drawing.
Expected Learning
- Name and distinguish the seven prototyping methods (paper, Wizard of Oz, wireframing, Hi-Fi mockup, interactive prototype, vertical prototype, horizontal prototype).
- Explain what Wizard of Oz prototyping is, when it is appropriate, and what its risks are.
- For a given scenario, recommend an appropriate prototyping method and justify the choice with reference to the UCD stage, the research question, and practical constraints.
- Understand exam sketching expectations: labelled screens, captions, and explicit links to requirements.
Past Paper Questions
Wizard of Oz appears in 2018 Q6 and 2021 Q5. Prototyping method selection appears in 2023 Q6 (mindfulness app). Sketching designs appears in 2025 Q5 (career-guidance app — sketch screens), 2024 Q5 (ChatGPT — sketch design screens), and 2021 Q5 (timepiece — Lo-Fi alternatives).