A. Design Processes and Related Skills · Design Skills: From Idea to Tested Prototype

Criteria, Constraints and Evaluation Measures

A1.5 A1.2About 70 minutes

Learning goals

I can tell the difference between criteria and constraints.
I can write qualitative and quantitative criteria that are clear and testable.
I can link each criterion to a technological concept.
I can use a weighted decision matrix to choose between design ideas.

Words to know

criterion (plural criteria)
A standard a design must meet to be successful, such as "holds 2 kg".

constraint
A limit the designer must work within, such as budget, time, size, materials or rules.

quantitative
Measured with numbers: mass, length, time, cost, temperature, force.

qualitative
Described with words or judgments: comfort, appearance, ease of use, taste. Often rated on a scale to make it easier to compare.

rating scale
A numbered scale, such as 1 (poor) to 5 (excellent), used to turn opinions into data.

decision matrix
A table that scores several ideas against weighted criteria to help choose the best one.

weight
A number that shows how important a criterion is compared with the others.

How will you know it worked?

Imagine you finish building something and someone asks, "Is it good?" If you planned well, you can answer with evidence: "Yes. It held 2.4 kg, it cost $3.10, and the user rated it 5 out of 5 for comfort."

That is why professionals set evaluation criteria before they build. The curriculum asks you to establish qualitative and/or quantitative criteria for evaluating products, services or processes, linked to technological concepts.

Criteria and constraints

Criteria describe what success looks like. They are goals: "The stand holds a tablet at an angle the user can choose."
Constraints are limits you cannot break: "Budget $5. Use only materials from home. Finished by Friday. Must fit on a 40 cm × 30 cm placemat."

A quick test: criteria are things you try to do well; constraints are walls you must stay inside.

Qualitative and quantitative criteria

Quantitative criteria use numbers and units: holds at least 1 kg; costs less than $5; ready in under 10 minutes; water stays above 60 °C for 30 minutes.

Qualitative criteria describe qualities: comfortable, attractive, easy to understand, tastes good. They matter a lot, but "comfortable" is hard to check. Make them testable by using a rating scale or a checklist: the user rates comfort 4 or 5 on a 5-point scale, or a first-time user can follow the instructions without asking for help.

Technological concept	Vague goal	Testable criterion	Type
Structure	It should be strong	Supports a 1 kg tablet for 24 h with no visible sagging	Quantitative
Ergonomics	Comfortable to use	User adjusts the angle with one hand in under 5 s and rates comfort ≥ 4/5	Both
Function	Holds the tablet	Holds a tablet at 3 different angles between 45° and 75°	Quantitative
Aesthetics	Looks nice	User rates appearance ≥ 4/5; no visible glue or tape	Qualitative (rated)
Sustainability	Eco-friendly	At least 80% of the material (by mass) is recycled or recyclable	Quantitative
Safety	Safe	No sharp edges or corners: passes a finger-run check; corners rounded to at least 5 mm radius	Both

Each criterion is tied to a technological concept and can actually be checked.

A quantitative criterion turns "stable" into a number: the stand must need at least 5 N of push at the top edge before it tips. Prototypes A and C pass (above the dashed line); prototype B fails.

Worked example

Writing criteria for a service

Ethan's class is planning the hot chocolate booth. Write two quantitative criteria, two qualitative criteria and three constraints.

Quantitative: (1) Each customer waits no more than 5 minutes (timed for 10 random customers). (2) Hot chocolate in the urn stays between 60 °C and 65 °C (checked with a food thermometer every 15 minutes): hot enough to enjoy, but not so hot that it scalds easily. Servers still warn each customer that the drink is hot.
Qualitative (made testable): (1) Customers rate taste 4 or 5 out of 5 on a quick sticker survey. (2) The booth looks clean and organized, judged by the teacher with a checklist (spills wiped, garbage in bin, cups stacked).
Constraints: budget of $60 from student council; 90 minutes of serving time; must follow the school's food safety rules (hand washing, hair tied back, no one serves if sick).
Link to concepts: wait time → function and systems; temperature → safety; taste → aesthetics.

Good criteria are specific and checkable; constraints are clear limits. Together they define success before the carnival starts.

Choosing between ideas: the weighted decision matrix

Once you have several ideas, score each one against your criteria.

List the criteria and give each a weight (for example 1 = nice, 2 = important, 3 = essential).
Score each idea from 1 to 5 for each criterion.
Multiply each score by the weight.
Add the products. The highest total is usually the best choice, but check that it does not fail any must-have criterion or break a constraint.

Worked example

Amira's decision matrix

Amira has three ideas. Weights: stability 3, ease of adjusting 3, cost 2, appearance 1. Scores (1 to 5): A notched cardboard: 4, 5, 5, 2. B wood with a screw knob: 5, 2, 3, 5. C folded acrylic: 3, 4, 2, 4. Which should she choose?

Idea A: 4×3 + 5×3 + 5×2 + 2×1 = 12 + 15 + 10 + 2 = 39
Idea B: 5×3 + 2×3 + 3×2 + 5×1 = 15 + 6 + 6 + 5 = 32
Idea C: 3×3 + 4×3 + 2×2 + 4×1 = 9 + 12 + 4 + 4 = 29
The maximum possible is 5 × (3 + 3 + 2 + 1) = 5 × 9 = 45.
Check must-haves: Sami needs to adjust without pinching. Idea B's screw knob scores only 2 there, which confirms it is a poor fit even though it looks best.

Choose Idea A (39/45). Its weakest area, appearance, could be improved later with paint or a wood-grain paper cover.

A weighted decision matrix drawn as stacked bars. Each segment is a score (1 to 5) times the criterion's weight. Idea A has the highest total (39 out of 45), mostly because it is easy to adjust and cheap.

Hands-on activity

Criteria for a lunch container

You need: two or three different food containers from your kitchen, water, a measuring cup, a kitchen scale (optional), a timer, and a notebook. Do this at the sink.

Write three quantitative and two qualitative criteria for a school lunch container (for example: holds at least 500 mL; does not leak when turned upside down for 10 s; opens in under 5 s; easy to clean; looks appealing).
Write two constraints (for example: fits in your backpack's side; costs under $10).
Test each container against your criteria. Fill with 250 mL of water and turn it over above the sink for the leak test. Rate the qualitative ones on a 1 to 5 scale and ask a family member to rate them too.
Build a weighted decision matrix and pick a winner.

What to look for: criteria with numbers and units, rating scales for qualitative ones, a completed matrix with correct multiplication, and a sentence explaining whether the winner fails any must-have.

Just for fun

A designer's to-do list: (1) Make it strong. (2) Make it light. (3) Make it cheap. (4) Make it beautiful. (5) Have it done by Friday.

That is not a to-do list. That is the reason constraints and weights were invented.

Your turn

Criterion or constraint? (a) must be finished in 2 weeks (b) holds at least 3 kg (c) budget $20 (d) user rates it easy to use ≥ 4/5

Quantitative or qualitative? (a) tastes sweet (b) costs under $4 (c) boils water in 3 min (d) looks modern

Make this qualitative criterion testable: "The poster should be easy to read."

Which technological concept does "supports 5 kg without bending more than 2 mm" relate to?

Weights: cost 2, strength 3. Idea X scores cost 4, strength 3. Idea Y scores cost 2, strength 5. Which has the higher weighted total?

In the tipping test, why did prototype B fail?

Why should criteria be set before building?

More practice: warm-up

What is a criterion?

What is a constraint?

Give an example of a quantitative criterion for a chair.

Give an example of a qualitative criterion for a meal.

What does a weight show in a decision matrix?

More practice: on your own

Write one criterion for each concept for a reusable shopping bag: structure, ergonomics, sustainability.

An idea scores highest in a decision matrix but breaks a constraint (it costs $30 when the budget is $20). What should the designer do?

Calculate the maximum possible total for a matrix with weights 3, 2, 2, 1 and scores out of 5.

Explain why "user rates comfort ≥ 4/5" is still partly qualitative.

Write a quantitative criterion for a hairstyling service.

Challenge

A team weights cost 1 and appearance 5 for a wheelchair ramp. Critique these weights.

Ideas P and Q are tied at 34 points. Describe two fair ways to break the tie.

Design a qualitative and a quantitative criterion for the process (not the product) of building a birdhouse in a class.

Check your understanding

Quiz

Which is a constraint?

Which criterion is quantitative?

Which makes "comfortable" testable?

Weights: 3 and 2. Scores: 4 and 5. Weighted total?

A criterion "rounded corners, no sharp edges" links mostly to...

Why set evaluation criteria before building?

For parents and teachers

Big idea: Expectation A1.5 asks students to establish qualitative and/or quantitative evaluation criteria linked to technological concepts. Clear criteria make the testing lessons later in the unit possible.

How to help at home:

When buying something (a phone plan, a winter coat), think aloud about your criteria, weights and budget constraints. Your teen will see that adults use the same process.
Volunteer as a second rater for qualitative criteria in the activity.

Common difficulties:

Mixing up criteria and constraints. Ask: "Is this something to do well, or a limit you can't cross?"
Vague criteria ("strong", "nice"). Ask: "How would we measure that?"
Arithmetic slips in the matrix. Encourage a calculator and a check that each total is no more than the maximum.

Safety: do the leak test over a sink; use cold water only.