The big idea: Development is a loop: model the cheapest thing that answers the current question, test it with real users, refine the design because of what happened — then go round again with a harder question.
You stop when every essential criterion has been measured and met.
Three real loops of one product. Each names what was built, what was measured and what changed.
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| Loop | Built | Measured | Changed |
|---|---|---|---|
| 1 | Card and foam at full size, no mechanism, an hour's work | 8 patients mimed reaching from a bed at the correct height | The surface must come 120 mm further over the bed than assumed |
| 2 | Printed arm and pivot on a weighted column | 12 patients swung it in and out; effort and hand position recorded | The handle moved to the front edge, because everyone gripped the corner |
| 3 | Working prototype in the intended materials | 5 kg at 50 mm from the edge, on a ramp, with nurses timing repositioning | No wheel lift; repositioning 6.2 s, so the brake lever was made larger |
A loop where nothing changed was not a test: If you build a model, show it to people, and change nothing, you ran a demonstration.
Either the question was one you already knew the answer to, or the test was not hard enough to fail. Both are worth noticing at the time.
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Managing the loops
Raise fidelity only as far as the question needs
A reach question needs a shape at the right height, not a working mechanism. Building more than the question requires costs time you will need later.
One question per loop
Change one significant thing at a time. If you change the arm length and the pivot together and it improves, you do not know which did it.
Test with the same kind of user each time
Comparing loop 3 on classmates against loop 1 on patients proves nothing. Same population, same task, same measurement.
Stop when the essentials are met, and say so
Not when the deadline arrives and not when it looks finished. Record which criteria are met, and which are not yet — that honesty is assessed.
What the folder has to show: For each loop: a photograph of what you built, the data you collected, and the change you made because of it.
A page of prototype photographs with no data between them shows activity rather than development.
How this is tested — demonstrating iterative development through the model, test, refine cycle. It comes up two ways:
Paper 1 — multiple choice
- Identify which part of the cycle an activity belongs to.
- Pick the correct next step after a test result.
Paper 2 — analysing a product
- Demonstrate iterative development of a named product across three loops.
- Explain why fidelity rises across the loops.
The trap: Describing three prototypes without saying what each test measured or what changed as a result. The marks are in the CHANGES, not in the models.
Demonstrate how the model, test, refine cycle would be used to develop a swinging bedside table surface, across three loops.
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