The big idea: A design specification turns research findings into criteria a solution can be judged against.
Every line comes from a finding, states what the solution must do, says how it would be tested, and is banded essential or desirable.
One line built from a finding to a testable criterion, three times over, then the essential-desirable split.
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Essential
- The solution fails without it
- Safety, the core task, anything a regulation demands
- Used as a filter — an idea that misses one is out
- "Stable with 5 kg placed 50 mm from the working edge"
Desirable
- A real improvement you take if it costs nothing else
- Comfort, appearance, convenience, extra capability
- Used as a tie-break between ideas that all pass
- "Height adjustable without tools"
Marking everything essential destroys the tool: If twelve criteria are all essential, nothing can be traded against anything, and the first real conflict stops the project.
The split exists so that a trade-off can be made honestly and in advance, rather than quietly, late, in favour of whatever is easiest.
| Finding | Criterion | How you would test it | Band |
|---|---|---|---|
| Tips at 4 kg 80 mm from the edge; 9 of 12 twisted to reach | Stable with 5 kg placed 50 mm from the working edge | Load a model at that point and check it does not lift a wheel | Essential |
| Nurses reposition it several times a shift, hands full | Movable and parked with one hand in under 5 seconds | Time 10 nurses moving it clear of a bed and back | Essential |
| Cleaners lose time working round the base | Base clearable in one movement with a floor mop | Ask 6 cleaners to clean a bay and time it | Desirable |
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Turning a wish into a criterion
Start from the finding, not from the product
Every line should be traceable to something you observed, counted or were told. A criterion with no source behind it is a preference.
Say what it must DO
"Stable when loaded at the working edge" describes behaviour. "Made from steel" describes a solution and rules out better ones.
Attach a number or a condition
5 kg at 50 mm. Under 5 seconds. After 200 wipes. Without a number, nobody can agree afterwards whether it was met.
Write the test at the same time
If you cannot say how you would check it, it is a wish. Writing the test now also means the evaluation at the end is already planned.
The specification is used three more times: To judge ideas against each other, to decide when development is finished, and to structure the final evaluation.
That is why a vague specification costs marks three stages later, long after it was written.
How this is tested — constructing testable specification criteria and banding them. It comes up two ways:
Paper 1 — multiple choice
- Identify whether a stated criterion is testable.
- Classify a criterion as essential or desirable.
Paper 2 — analysing a product
- Construct specification criteria for a named product from given findings.
- Explain why criteria are split into essential and desirable.
The trap: Writing the material or the shape into the criterion. "Made from aluminium" is a solution; the criterion is the behaviour you wanted aluminium for.
From the ward findings — the table tips at 4 kg placed 80 mm from the edge, nurses reposition it several times a shift with their hands full, and cleaners lose time working round the base — construct three specification criteria and band each one.
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