Fishbone Diagram (Also Called: Cause-and-Effect Diagram, Ishikawa Diagram)
Variations: cause enumeration diagram, process fishbone, time-delay fishbone, CEDAC
(cause-and-effect diagram with the addition of cards), desired-result fishbone, reverse
Description: Represents the relationship between an effect (problem) and its potential
causes. Categorizes causes. The fishbone diagram identifies many possible causes for an
effect or problem. It can be used to structure a brainstorming session. It immediately sorts
ideas into useful categories.
When to Use: 1. When identifying possible causes for a problem. 2. Especially when a
team’s thinking tends to fall into ruts.
Procedure: Materials needed: flipchart or whiteboard, marking pens.
1. Name the problem or effect of interest; Agree on a problem statement (effect). Write it at
the center right of the flipchart or whiteboard. Draw a box around it and draw a horizontal
arrow running to it.
2. Decide the major categories for causes by brainstorming the major categories of causes of
the problem. If this is difficult use generic major cause headings - the 6 M’s:: Methods;
Machines (equipment); People (manpower); Materials; Measurement; Environment
3. Write the categories of causes as branches from the main arrow.
4. Brainstorm all the possible causes of the problem. Ask: “Why does this happen?” As each
idea is given, the facilitator writes it as a branch from the appropriate category. Causes can
be written in several places if they relate to several categories. Ask "why" each major cause
happens at least 5 times
5. Eliminate causes that do not apply. Again ask “why does this happen?” about each cause.
Write sub-causes branching off the causes. Continue to ask “Why?” and generate deeper
levels of causes. Layers of branches indicate causal relationships. Brainstorm for more ideas
in those categories that contain fewer items. This helps counter the “theme” or “group think”
effect common in brainstorming
6. When the group runs out of ideas, focus attention to places on the chart where ideas are
few. Discuss the causes and decide which are most important. Work on most important root
causes. Perform another iteration to determine root causes if necessary
Why: To help ensure that a balanced list of ideas have been generated during brainstorming;
Sort and relate the factors affecting a process while little quantifiable data is available; Assist
discussion when determining root causes; To determine the real cause of the problem (as
opposed to a symptom of the problem); To refine brainstormed ideas into more detailed
causes; To identify a team's level of understanding
More on the “Theme” Effect:
-Very often, brainstorming sessions tend to go off in a particular direction based on a common
-One or two good ideas get the rest of the group thinking along those lines.
-The rest of the brainstorming session continues along this “theme.”
-The cause & effect diagram helps overcome the “theme” effect by allowing the group to
visualize the categories into which their ideas fall.
-The group can then be redirected to focus on generating more ideas in those categories that
Cause & Effect Diagram Conclusions
-Represents the relationship between an effect (problem) and its potential causes.
-Helps ensure that a balanced list of ideas have been generated during brainstorming
-Helps us overcome the “theme” or “group think” effect
-Sorts and relates the factors affecting a process while little quantifiable data is available
-Serves as a discussion guide to assist in determining root causes
-Helps determine the real cause of the problem as opposed to just highlighting a symptom of
-Helps refine brainstormed ideas into more detailed causes
-Helps identify a team's level of understanding
Management Man Method
Cause Cause Cause
Measurement Machine Material
Cause and Effect…