To compare design alternatives fairly, write the criteria first and judge each alternative against the same list. The decision then follows from the comparison, not from which sketch you prefer.
This lesson is part of SPM subjects and learning resources. It pairs with connecting an observed user need to a product sketch.
How do you write useful criteria?
Make each criterion testable. “Strong” is vague. “Holds a school bag weighing 3 kg without bending” can be tried.
Write four or five criteria and put the most important first. That order helps you justify the final decision.
Worked example: two invented bag hooks
The learner designs a hook for the side of a classroom desk. Criteria: holds a 3 kg bag, fits desk edges up to 2.5 cm thick, does not scratch the desk, and can be used one-handed.
Alternative A is a U-shaped clip of bent metal strip with a hook at the end. Alternative B is a hinged plastic hook with a soft rubber pad and a spring.
| Criterion | Alternative A | Alternative B |
|---|---|---|
| Holds 3 kg | Passes, the metal does not bend when loaded with books | Partly, the spring sags slightly under load |
| Fits 2.5 cm edge | Passes, clip opening is 2.8 cm | Passes, hinge adjusts |
| No scratching | Fails, bare metal touches the desk | Passes, rubber pad |
| One-handed use | Partly, needs a tilt to slide on | Passes, clips on by pressing |
No alternative wins every row. A passes the strength test and B passes use and protection.
Making the decision
Count the passes, then look at which criteria matter most. If strength is the first priority, A’s pass on load counts heavily, but the scratch fail is a real fault.
A justified decision might be: “I choose A and add a rubber sleeve on the contact points, which fixes the only fail. B’s sag under load is harder to fix without a thicker spring.”
The mistake to avoid
The common slip is to decide first and write criteria afterwards so that the favourite wins. The criteria then look fair, but they were shaped to fit.
Write criteria before you sketch the alternatives, or at least before you compare. If you change a criterion later, record why.
Check yourself
A third alternative, C, is a simple adhesive hook stuck under the desk. It passes one-handed use and no scratching, but the adhesive slips with a 3 kg load and the desk edge thickness does not matter. Fill in C’s row and say what it tells you.
Answer
Holds 3 kg: fails. Fits 2.5 cm edge: not relevant, because it does not use the edge, so record this as not applicable. No scratching: passes. One-handed use: passes.
C fails the most important criterion, so it should be dropped or redesigned with a stronger fixing. A and B still compare better.
What to study next
Write your own criteria and check the sentences with the structured-answer self-review tool. For a teacher to review your criteria and sketches, see online one-to-one Industrial Design tuition.