Concept Selection - A Method That Works

Summary

Stuart Pugh presents a non-numeric concept selection procedure intended to reduce "conceptual vulnerability" in engineering design. The method uses comparable concept sketches, agreed evaluation criteria, a datum concept, and repeated matrix comparisons using plus, minus, and same judgments. Its purpose is controlled convergence on strong concepts while preserving discussion, understanding, and defensible reasoning rather than relying on numerical weighting.

Important Keywords

Concept selection: choosing among alternative product concepts through structured comparison.
Conceptual vulnerability: the openness of a concept to critique and improvement during evaluation.
Concept comparison and evaluation matrix: Pugh's matrix for comparing concepts against criteria and a reference concept.
Datum concept: the reference concept against which other alternatives are judged.
Product specification: the criteria or requirements used to evaluate competing concepts.
Controlled convergence: narrowing alternatives through repeated comparison while retaining useful features.
Non-numeric evaluation: judging alternatives with relative signs or qualitative comparisons rather than weighted scores.
Design teaching and practice: the paper's concern with making concept selection usable for designers and students.
Concept: a formed, communicable idea with enough detail for shared understanding and evaluation.
Design rationale: explanation of decisions, alternatives, and trade-offs behind a design.
Design space: map of possible alternatives and evaluation criteria.
QOC: Questions, Options, Criteria representation of design reasoning.
Multivoting: quick group method for narrowing a larger option set.

Important Concepts

Conceptual weakness can arise either from choosing a weak concept or from choosing a strong concept without understanding or being able to defend why it is strong.
Concepts should be compared at the same generic level and with sketches developed to the same level of detail.
Evaluation criteria should come from the product specification and be unambiguous to all participants.
Concepts are compared against a datum using +, -, and S rather than numerical scores or weighted ratings.
Re-running the matrix with changed datums, removed strengths, refined concepts, and expanded criteria tests whether an emergent pattern persists.
The matrix supports disciplined debate and understanding; it does not make the decision for the designers.
The procedure is intended to reduce premature intuitive choice, false confidence from numeric methods, and constraints on creative thinking.
Concept selection should be grounded in user needs, empirical findings, case-specific criteria, and documented reasoning rather than personal preference alone.
Common selection methods include external decision, product champion, intuition, multivoting, pros/cons, decision matrices, and prototype-and-test.
A concept screening matrix rates concepts against criteria, ranks them, supports combination/improvement, and documents why choices were made.
Design rationale records why an artifact is designed as it is, including alternatives, arguments, trade-offs, justifications, and rejected options.
QOC structures design reasoning as Questions, Options, and Criteria.

Examples

Students applied the procedure to generate concepts for an audible means of approach for a motor car, using the traditional motor horn as the datum. Fourteen comparable concepts were evaluated against criteria such as sound level, frequency range, resistance to corrosion and vibration, response time, complexity, power consumption, maintenance, weight, size, number of parts, service life, manufacturing cost, installation, and shelf life. Concept 5 emerged as especially strong in the evaluation.