The big idea: Ideas are compared against the design specification and user needs — never against which one you like.
Put the criteria in the rows and the ideas in the columns, score every cell, and the reasoning becomes something you can show somebody else.
Score, filter on essentials, break ties on desirables, then combine. Step through — the order matters more than the arithmetic.
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Reading a comparison matrix properly
Score every cell first
3 fully meets it, 2 partly, 1 does not. Score against the criterion as written, including its number — not against how you feel about the idea.
Remove anything failing an ESSENTIAL
However well it scores elsewhere. An idea that cannot be used one-handed fails the thing the project exists for, and cheapness does not buy that back.
Use desirables on the survivors
Now cost, cleaning and adjustability choose between ideas that all pass. This is the only place a total is worth looking at.
Take the user needs back out
Check the survivor against the persona, not only the numbers. A table that scores well and that a patient would be embarrassed to use has failed a need nobody wrote down.
Never add the columns up: Summing the scores lets four small desirables outvote one essential, which is exactly the decision the essential-desirable split exists to prevent.
Filter first, then compare. A total computed before the filter is meaningless.
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The statement says iterative analysis leads to IMPROVED design ideas — not to a winner. In practice comparison shows you which part of each idea was doing the work, and the developed design takes the best parts of more than one.
| Idea | What it was good at | What killed it | What survived into the design |
|---|---|---|---|
| Wheeled trolley | Familiar, cheap, easy to clean under | Still has to be pulled into place one-handed | The clear, moppable base |
| Wall-mounted arm | No floor contact at all, so cleaning is trivial | Needs a structural fixing in every bay, so it cannot be retrofitted | The idea of the surface moving, not the table |
| Counterbalanced swing arm | Brings the surface to the patient with one hand | Cost, and a mechanism that must be cleanable | The counterbalance, sealed inside the column |
Record why, not just which: The comparison is assessed on its reasoning. A matrix with scores and no sentences is a table of numbers whose origin nobody can check.
Under each column, say what the score means and what you did about it.
How this is tested — comparing ideas against the specification and user needs, and refining from the comparison. It comes up two ways:
Paper 1 — multiple choice
- Identify which idea survives a stated essential criterion.
- Pick the correct use of a comparison matrix.
Paper 2 — analysing a product
- Compare ideas for a named product against given criteria.
- Explain how comparison leads to an improved idea rather than a winner.
The trap: Adding the scores up and picking the biggest total. That lets several small desirables outvote one essential, which is the decision the split was designed to prevent.
Three ideas for a bedside table — a wheeled trolley, a wall-mounted arm and a counterbalanced swing arm — are compared against the specification. Evaluate how the comparison should be carried out and what it should produce.
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