Two of the most commonly confused terms in C4-2 are *efficiency* and *effectiveness*. The rubric treats them as distinct — and the evaluation matrix has separate tables for each. Getting them confused means applying the wrong criteria to your design ideas.

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| Term | One-sentence definition | Core question |

|---|---|---|

| **Efficiency** | How well the software uses resources (time, memory, processing) to do its job | "Does it do this **fast enough** and at **low enough cost**?" |

| **Effectiveness** | How well the software meets the needs of its users and fulfils its purpose | "Does it do the **right thing** for the **right people**?" |

These are not synonyms. A system can be highly efficient (fast, lean) but completely ineffective (solves the wrong problem, confuses users). A system can be highly effective (users love it, every requirement met) but inefficient (slow, resource-heavy).

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Imagine two versions of a student event-booking app:

| Scenario | Version A | Version B |

|---|---|---|

| Loads event list in | 0.3 seconds | 4.5 seconds |

| First-time users can complete a booking without help | 30% | 90% |

| Verdict | **Efficient, not effective** | **Effective, not efficient** |

Version A is fast but unusable for most students — it fails effectiveness.

Version B is slow but most students can use it independently — it fails efficiency.

The best design scores well on *both*.

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In your evaluation matrix, each table uses separate factors:

**Efficiency factors** (measure resource use):

- Speed of Processing (time)

- Cost of Data Manipulation

- Functionality Implementation (effort/complexity)

- Hardware Requirements

- Bandwidth Usage (if applicable)

**Effectiveness factors** (measure fitness for purpose):

- Usability, Accessibility, Clarity, Completeness, Accuracy, Relevance, Readability, Attractiveness, Maintainability, Timeliness, Communication of Message

When writing criteria, make sure each criterion lands in the right table. "The app loads in under 2 seconds" is an efficiency criterion. "80% of users can book an event without assistance" is an effectiveness criterion.

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At **5–6**, you must *develop and apply evaluation criteria*. This requires criteria in both tables — not just one.

At **7–8**, you must *explain* which design elements should proceed, referencing your criteria scores. Mixing up efficiency and effectiveness makes your explanations incoherent.

At **9–10**, you must *justify* decisions with clear reasoning from scores to SRS requirements. The distinction between efficiency and effectiveness must be held precisely throughout.

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- [Evaluation vs Testing](/sd/C04/Evaluation%20vs%20Testing) — the other common conflation

- [C04 Resources](/sd/Resources/C04-Resources) — external reading on efficiency and effectiveness

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