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Also called: systematic diagram, tree analysis, analytical tree, hierarchy diagram

Description

The tree diagram starts with one item that branches into two or more, each of which branch into two or more, and so on. It looks like a tree, with trunk and multiple branches.

It is used to break down broad categories into finer and finer levels of detail. Developing the tree diagram helps you move your thinking step by step from generalities to specifics.

When to Use a Tree Diagram

• When an issue is known or being addressed in broad generalities and you must move to specific details, such as when developing logical steps to achieve an objective.
• When developing actions to carry out a solution or other plan.
• When analyzing processes in detail.
• When probing for the root cause of a problem.
• When evaluating implementation issues for several potential solutions.
• After an affinity diagram or relations diagram has uncovered key issues.
• As a communication tool, to explain details to others.

Tree Diagram Procedure

1. Develop a statement of the goal, project, plan, problem or whatever is being studied. Write it at the top (for a vertical tree) or far left (for a horizontal tree) of your work surface.
2. Ask a question that will lead you to the next level of detail. For example:
• For a goal, action plan or work breakdown structure: “What tasks must be done to accomplish this?” or “How can this be accomplished?”
• For root-cause analysis: “What causes this?” or “Why does this happen?”
• For gozinto chart: “What are the components?” (Gozinto literally comes from the phrase “What goes into it?”

Brainstorm all possible answers. If an affinity diagram or relationship diagram has been done previously, ideas may be taken from there. Write each idea in a line below (for a vertical tree) or to the right of (for a horizontal tree) the first statement. Show links between the tiers with arrows.

3. Do a “necessary and sufficient” check. Are all the items at this level necessary for the one on the level above? If all the items at this level were present or accomplished, would they be sufficient for the one on the level above?
4. Each of the new idea statements now becomes the subject: a goal, objective or problem statement. For each one, ask the question again to uncover the next level of detail. Create another tier of statements and show the relationships to the previous tier of ideas with arrows. Do a “necessary and sufficient check” for each set of items.
5. Continue to turn each new idea into a subject statement and ask the question. Do not stop until you reach fundamental elements: specific actions that can be carried out, components that are not divisible, root causes.
6. Do a “necessary and sufficient” check of the entire diagram. Are all the items necessary for the objective? If all the items were present or accomplished, would they be sufficient for the objective?