Also called: systematic diagram, tree analysis, analytical tree, hierarchy diagram
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
- 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.
- 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.
- 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?
- 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.
- 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.
- 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?
Tree Diagram Example
The Pearl River, NY School District, a 2001 recipient of the Malcolm Baldrige National Quality Award, uses a tree diagram to communicate how district-wide goals are translated into sub-goals and individual projects. They call this connected approach “The Golden Thread.”
The district has three fundamental goals. The first, to improve academic performance, is partly shown in the figure below. District leaders have identified two strategic objectives that, when accomplished, will lead to improved academic performance: academic achievement and college admissions.
Tree Diagram Example
Lag indicators are long-term and results–oriented. The lag indicator for academic achievement is Regents’ diploma rate: the percent of students receiving a state diploma by passing eight Regents’ exams.
Lead indicators are short-term and process-oriented. Starting in 2000, the lead indicator for the Regents’ diploma rate was performance on new fourth and eighth grade state tests.
Finally, annual projects are defined, based on cause–and–effect analysis, that will improve performance. In 2000–2001, four projects were accomplished to improve academic achievement. Thus this tree diagram is an interlocking series of goals and indicators, tracing the causes of systemwide academic performance first through high school diploma rates, then through lower grade performance, and back to specific improvement projects.
Excerpted from Nancy R. Tague’s The Quality Toolbox, Second Edition, ASQ Quality Press, 2004, pages 501–504.
