The Causal Categories Behind Fishbone Diagrams

The effectiveness of the Fishbone Diagram, also known as Cause and Effect Diagram, lies not only in the organization and relation of causes, but in how we define its “bones.” These main branches—often called categories of causes—are what shape the quality of the analysis. Choosing the right categorization determines whether it uncovers meaningful root causes or simply generates a long, unfocused list of ideas.

The key idea is simple: the same problem can be analyzed through different lenses, and each lens will highlight different systemic weaknesses.

Why Categories Matter in the Fishbone Diagram

A Fishbone Diagram is only as strong as its structure. When categories are poorly chosen, discussions tend to drift into scattered brainstorming, often ending in vague actions like “improve training” or “add resources.”

Well-designed categories do three things:

• Focus thinking around the process, not the symptom

• Ensure coverage of all relevant contributing areas

• Translate findings into actionable improvement opportunities

This is why multiple structured frameworks can be used to support consistent categorization.

Traditional Frameworks for Cause Categorization

Different contexts require different lenses. Over time, several standard models have been used to structure Fishbone Diagrams in a more systematic way.

5M/1E Model (Generic)

One of the most widely used frameworks, especially in technical and operational environments:

• Machine: Equipment and physical systems involved in the process

• Methods: Procedures, workflows, and operational practices

• Measurements: Data collection, KPIs, and monitoring systems

• Materials: Inputs, consumables, and resources

• Manpower: Skills, staffing, and human capability

• Environment: Physical and external conditions affecting performance

This model is particularly effective when processes are stable but performance varies.

4S Model (Generic)

A more organizationally oriented structure:

• Systems: Formal processes and organizational routines

• Surroundings: Physical workspace and conditions

• Skills: Competencies and capability levels

• Suppliers: External contributors and dependencies

This framework is often used when the problem spans multiple departments or external interfaces.

8P Model (Marketing and Strategic Context)

Used in business performance, commercial operations, and strategy:

• Product: Service or output delivered

• Price: Cost structure and pricing logic

• Place: Distribution and accessibility

• Promotion: Communication and marketing

• People: Stakeholders and personnel involved

• Positioning: Market perception and competitiveness

• Processes: Operational workflows

• Performance: KPIs and results measurement

This model shifts the focus from operational faults to strategic alignment.

SHELL Model (Human Factors Focus)

Widely used in aviation and safety-critical industries:

• Software: Procedures, manuals, and regulations

• Hardware: Tools, equipment, and physical assets

• Environment: Working conditions and context

• Liveware: Human interaction and performance

This model is particularly effective when human-system interaction is central to the issue.

Dirty Dozen (Human Factors in Depth)

A more granular human factors framework frequently used in aviation safety is the Dirty Dozen:

Complacency, lack of communication, distraction, lack of teamwork, fatigue, lack of resources, pressure, lack of assertiveness, stress, lack of awareness, lack of knowledge, and norms.

Instead of treating “human error” as a category, it breaks it into specific behavioral and cognitive contributors.

TIMWOODS: Connecting Causes to Waste

A significant evolution in categorization came from applying Lean thinking to Fishbone Diagrams.

The TIMWOODS framework focuses on waste in processes:

• Transportation

• Inventory

• Motion

• Waiting

• Overproduction

• Overprocessing

• Defects

• Skills

Unlike traditional models, TIMWOODS directly connects causes to value loss in the process. This makes it easier to translate findings into operational improvements rather than abstract conclusions.

Within the context of The Lean Airline, this approach is particularly effective because it aligns root cause analysis directly with process mapping and continuous improvement cycles.

A Common Pitfall: The “People” Trap

Across frameworks, one recurring issue appears: the tendency to assign “people” as a root cause category.

Labels such as “man,” “manpower,” or even “people” often lead teams toward simplistic conclusions like:

• “They need more training”

• “Human error occurred”

• “Discipline should be improved”

This creates a loop of superficial solutions without addressing systemic contributors such as unclear processes, poor interface design, or workload imbalance.

The more effective approach is to translate “people problems” into process questions:

• What in the system made the error likely?

• What information was missing or unclear?

• What conditions increased cognitive load or pressure?

Root cause analysis should move away from individual blame and toward system design.

Choosing the Right Framework

There are no universally correct categories, but there are better fits depending on context and problem type The selection depends on:

• Nature of the problem (technical, operational, strategic, human factors)

• Industry context

• Level of complexity

• Desired outcome (waste reduction, safety improvement, performance optimization)

In practice, experienced teams often adapt or combine frameworks rather than using them rigidly.

The objective is not to complete a diagram, but to generate clarity that leads to action.

Conclusion

Cause and Effect categorization is not a theoretical exercise—it is the structure that determines the quality of problem-solving. Whether using 5M/1E, SHELL, Dirty Dozen, or TIMWOODS, the real value comes from how well the categories guide thinking toward system-level understanding.

The most effective Fishbone Diagrams are those that move beyond listing causes and instead reveal how processes, environments, and decisions interact to create outcomes.

When used correctly, categorization becomes less about organizing ideas and more about revealing how the system actually behaves.

Learn to uncover root causes and solve problems effectively →