UX Glossary · A
Affinity diagram
Also: Affinity map · Affinity mapping · KJ method
Grouping individual research observations by similarity until the themes emerge from the data.
An affinity diagram turns a pile of individual observations into a set of themes. Each observation goes on its own note, the notes are grouped by similarity, and the groups are named only after they have formed.
The method comes from the Japanese anthropologist Jiro Kawakita, who developed it in the 1960s. It is still sometimes called the KJ method after his initials.
Why the order matters
The discipline is in naming the groups last. Deciding the categories first and sorting observations into them tests a hypothesis you already had. Letting groups form from similarity lets the data say something you did not expect, which is the entire point of qualitative research.
In practice
After ten interviews you might have 300 notes. Grouping them typically yields somewhere between five and ten themes, each supported by observations from several different participants. A theme carried by a single participant is a quote, not a finding, and labelling it as such keeps the synthesis honest.
Doing this as a team also has a side effect worth having: everyone who sorts the notes ends up having read the raw data, which makes the findings much harder to dismiss later.