SC QUALITY GUILDAffinity diagram
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Write the ideas on cards, sort them into natural groups, and give each group a header card. The diagram draws itself and the checks point out loose cards, groups of one and headers that are only labels.
ON THE EXAM · CQPA II.D.1, CQE V.B.1, CSSBB IV.D.1, CMDA V.A · FREE · NOTHING YOU TYPE LEAVES YOUR BROWSER
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What an affinity diagram is for
An affinity diagram organizes a large number of ideas, opinions or facts into a few groups by their natural relationships. It is the first of the seven management and planning tools, and it is used when the material is too large or too vague to analyze directly: the output of a brainstorm, interview notes, open survey answers, a pile of complaints. The result is a short list of themes that the team agrees on and can work with.
It is a tool for language data, not numbers. It finds structure; it does not rank the groups or prove what causes what.
How to run it
- State the question as a full sentence, so everyone is answering the same thing.
- Write one idea per card, in a few words with a verb: "Test bench down twice a week", not "Bench" and not a paragraph.
- Sort in silence. Everyone moves cards at the same time, without discussion. If a card keeps moving between two groups, make a copy. Silence stops the loudest person setting the categories.
- Discuss and adjust once the groups have settled. A card that fits nowhere can stay alone.
- Write the header cards last. A header is a short statement that captures what the cards in the group have in common.
Good header cards
The header carries the meaning of the group to someone who never reads the cards. "Training" is a label; "Only one person is trained on the test bench" says something. Headers written as statements make the groups easier to act on and are what the next tool uses: the header cards are usually the issues placed on an interrelationship digraph.
Reading the checks
- Ungrouped cards are the unfinished work. Place them, or keep them as deliberate loners.
- Groups of one are often a header in disguise or a card that belongs elsewhere.
- Too many groups (more than about ten) means the sorting stopped too early. Look for groups that say the same thing.
- One very large group often holds two ideas. Split it, with subheaders.
Affinity diagram, brainstorming or fishbone?
Brainstorming generates the ideas; the affinity diagram organizes them. A cause and effect diagram sorts causes into categories chosen in advance (such as the 6Ms). The affinity diagram lets the categories come out of the cards, which is why it suits new or messy problems where nobody yet knows the right categories.
On the exam
Affinity diagrams are listed among the quality management tools in CQPA (II.D.1), together with force field analysis in CQE (V.B.1), among the analytical tools in the CSSBB Define section (IV.D.1), and among the quality control and problem-solving tools in CMDA (V.A). Expect questions on when to use one (large amounts of unorganized language data), on the silent sorting step, and on what a header card is.