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Learn About Quality

What is a Tree Diagram?

Quality Glossary Definition: Tree diagram

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

A tree diagram is a new management planning tool that depicts the hierarchy of tasks and subtasks needed to complete and objective. The tree diagram starts with one item that branches into two or more, each of which branch into two or more, and so on. The finished diagram bears a resemblance to a tree, with a 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 interrelationship 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, ask: "What tasks must be done to accomplish this?" or "How can this be accomplished?"
    • For root-cause analysis, ask: "What causes this?" or "Why does this happen?"
    • For a Gozinto chart, ask: "What are the components?" ("Gozinto" literally comes from the phrase, "What goes into it?")
  3. Brainstorm all possible answers. If an affinity diagram or interrelationship 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.
  4. 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?
  5. 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.
  6. 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.
  7. 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

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 a 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.

Adapted from The Quality Toolbox, Second Edition, ASQ Quality Press.

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