Brainstorming and Affinity Diagram: Generate and Group Ideas

What brainstorming and the affinity diagram are

Brainstorming is a technique for generating many ideas in a short time without judging them. The affinity diagram is the next step: sorting those ideas into groups by natural similarity, naming each group and seeing the themes of the problem. Together they turn a pile of loose suggestions into a prioritized set.

Brainstorming was popularized by Alex Osborn in the 1950s. The affinity diagram comes from the KJ method of Jiro Kawakita and is one of the planning tools used in quality management.

Visual map: from brainstorming to grouping

The map shows the rules, the steps and the example of 24 ideas grouped and voted on.

The 4 rules of brainstorming

1. Quantity over quality. More ideas raise the chance that a good one appears.
2. No criticism while generating. Judging on the spot silences the group.
3. Wild ideas are welcome. An exaggerated idea can lead to a workable one.
4. Combine and build on other people's ideas.

Set a clear, bounded question, for example "How can we reduce crooked labels on the filling line?", and a fixed time. Vague questions like "how do we improve quality?" produce vague answers.

Shop floor tip: start with 3 to 5 minutes of silent writing, each person with their own cards. This keeps the boss or the loudest voice from steering the group. Then each person reads their ideas aloud and the facilitator posts the cards on the board.

Affinity diagram: 7 steps

1. Define the question and write it at the top of the board.
2. Generate ideas by brainstorming: one idea per card, a short complete sentence.
3. Spread the cards on the board in no order.
4. Group in silence: everyone moves cards next to those that seem related. A card that keeps changing place is often a group of its own.
5. Name the groups with a header card describing the theme (a phrase, not a single word).
6. Vote: each person gets points (for example 3) to distribute among the groups.
7. Define actions for the top-voted groups, with an owner and a deadline.

Groups should emerge from the ideas, not from ready-made categories. If you already know the categories (6M, for instance), use the Ishikawa (fishbone) diagram. Affinity is better when the problem is poorly structured.

Example: crooked labels on the filling line

Fictional example. A team of 5 people (operator, mechanic, quality, logistics and supervisor) answers the question "How can we reduce crooked labels on the filling line?". In 10 minutes they produce 24 ideas. After silent grouping, 5 groups appear:

Check: 6 + 5 + 5 + 4 + 4 = 24 ideas. Each of the 5 people spread 3 votes: 5 × 3 = 15 votes, and 6 + 4 + 2 + 2 + 1 = 15. The Machine group got 6 of 15 votes, or 40%, and becomes the first focus.

Without this step, the meeting would end with 24 suggestions and no decision. With it, the team knows where to start.

What to do with the result

• Turn the top group into actions in a 5W2H plan: what, who, when, where, why, how and how much.
• If several ideas compete, use the GUT matrix to rank by severity, urgency and tendency.
• To reach the cause, take the group's cards and dig deeper with the 5 Whys.
• Test the action in the PDCA cycle before standardizing.
• Photograph the board and keep the record with date and participants.

Brainstorming and affinity sit alongside the seven quality tools but deal with ideas and opinions. When the decision depends on numbers, use collected data, for example in a check sheet.

Common mistakes

• Criticizing ideas during generation. Separate generating from evaluating.
• Letting the boss speak first, which steers the rest of the group.
• Groups that are too large. 5 to 8 people works best; above that, split into subgroups.
• Vague cards such as "improve" or "training", which cannot be grouped or acted on.
• Grouping by ready-made categories and missing unexpected themes.
• Stopping at the vote, with no owner, deadline or follow-up.
• Treating the vote as proof: it shows the group's opinion, not a verified cause. Confirm with data.

Frequently asked questions

What is brainstorming?

A group technique for generating as many ideas as possible about a question, without criticizing them during generation.

What is an affinity diagram?

A tool that groups ideas, opinions or data into themes by similarity and names each group, to organize poorly structured problems.

What is the difference between an affinity diagram and a fishbone?

In a fishbone the categories (such as the 6Ms) exist beforehand and causes are fitted into them. In an affinity diagram, the groups emerge from the ideas themselves.

How many people and how long?

5 to 8 people and 10 to 15 minutes of generation usually suffice; grouping and voting take another 20 to 30 minutes.

How do you pick the priority group?

With dot voting: in the example, 5 people with 3 votes each make 15 votes, and the group with 6 votes (40%) became the first focus.

Who created the KJ method?

The Japanese anthropologist Jiro Kawakita, whose initials give KJ, developed the method of grouping qualitative data into clusters.

About the author

Vagner Soares

Lean Manufacturing & Behavioral Management Specialist

Over 20 years in the automotive and metalworking industries (GM and Dana), Lean Manufacturing practitioner since 2006. SENAI instructor and mentor in Brazil’s Brasil Mais Produtivo program, delivering consulting, training and audits for 50+ companies, combining quality, productivity and people development.

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