Cause and Effect Diagram (Fishbone): Finding the Root Causes of Problems

When to Use a Cause and Effect Diagram

Use this tool when:

​

• A problem is complex or recurring

• The root cause is not immediately clear

• Multiple factors may be contributing

• You want to involve a team in structured problem-solving

​

It is commonly used in the Analyze phase of DMAIC, but can also support Define and Improve activities.

How a Cause and Effect Diagram Works

The process involves assembling a team of subject matter experts and begin the analysis:

​​

Define the Problem (Effect): Clearly state the problem at the “head” of the fish.
Draw the Main Spine and Branches: Create a central line (spine) with angled branches for categories.
Identify Major Cause Categories: Common categories include:

• People

• Process (Methods)

• Equipment (Machinery, Technology)

• Materials (Supplies)

• Environment

• Measurement

Brainstorm Possible Causes: Add contributing factors under each category.
Probe Deeper (Ask “Why?”): Use techniques like the 5 Whys to drill down into root causes.
Analyze and Prioritize: Identify the most likely root causes for further validation.

Key Concepts in Cause and Effect Analysis

Here are some of the distinguishing features of a cause and effect analysis:

​

• Effect (Problem Statement): The issue being analyzed

• Cause Categories: Groupings of potential contributing factors

• Root Cause vs Symptom: Distinguishing what drives the issue vs what results from it

• Structured Brainstorming: Organizing ideas visually to improve clarity

Common Pitfalls to Avoid

Cause and effect diagrams are powerful—but only when done correctly. Avoid these common mistakes:

​​

• Defining the problem too vaguely

• Jumping to conclusions without validating causes

• Overlooking categories or perspectives

• Treating all causes as equally important

• Failing to follow up with data analysis

Where the Cause and Effect Diagram Fits in Lean Six Sigma

The Cause and Effect Diagram is a core tool in:

​

• Analyze Phase (DMAIC): Identifying potential root causes

• Root Cause Analysis (RCA): Supporting deeper investigation

• Continuous Improvement Initiatives: Understanding process variation

​

It is often used alongside:

​

• 5 Whys

• Pareto Analysis

• Process Mapping

• Data collection and validation tools

​​​

What Is a Cause and Effect Diagram in Simple Terms?

​​​

It’s a way to break down a problem and visually map out all the possible reasons it might be happening.