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

When to Use a Cause and Effect Diagram

Use this tool when:

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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 but being a foundational tool for root cause analysis, it can be employed at any time when problem-solving is needed.

How a Cause and Effect Diagram Works

This tool or method can be adapted to serve any need, but typically involves:

Step 1: Define the Problem (Effect)

• Clearly state the problem at the “head” of the fish.

Step 2: Draw the Main Spine and Branches

• Create a central line (spine) with angled branches for categories.

Step 3: Identify Major Cause Categories - common categories include:

• People

• Process

• Equipment

• Materials

• Environment

• Measurement

Step 4: Brainstorm Possible Causes

• Add contributing factors under each category.

Step 5: Probe Deeper (Ask “Why?”)

• Use techniques like the 5 Whys to drill down into root causes.

Step 6: 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:

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• 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 analysis is 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 Cause and Effect Analysis 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​

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What Is a Cause and Effect Diagram in Simple Terms?

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