Cause-and-effect (Fishbone) diagram

1. The Layman’s Intro: The "Car Won't Start" Analogy

Understand the core logic of this tool using a simple, everyday analogy: troubleshooting a car that won't start.

Imagine you wake up, get into your car, turn the key, and hear nothing but a click. The car not starting is the "Effect" (the problem). If you were to draw this, "Car Won't Start" goes in a box at the far right, like the head of a fish.

Instead of randomly guessing what is wrong, you brainstorm major categories of potential issues to form the "bones" of the fish:

• Electrical: Is the battery dead? (If yes, why? Left the headlights on).
• Fuel: Is the gas tank empty? Is there a leak?
• Mechanical: Is the starter motor broken?
• Human Error: Is the car not actually in "Park"?

The Fishbone diagram visually organizes your troubleshooting process. It forces you to look at every possible category of failure rather than jumping to the most obvious conclusion. By repeatedly asking "Why?" along each "bone," you quickly trace the surface-level symptom back to its true root cause.

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2. Academic Lecture Note: The Cause-and-Effect Diagram

Historical Origin The Cause-and-Effect diagram was developed in 1943 by Kaoru Ishikawa, a pioneer in Japanese quality control. Ishikawa championed the idea of "democratizing statistics," which meant utilizing simple, effective visual tools that could be understood and applied by the entire workforce, not just statisticians and engineers. The technique became a cornerstone of the Japanese "quality circle movement" in the 1960s. Today, it is universally referred to as the Ishikawa diagram, the Fishbone diagram, or the Cause-and-Effect diagram.

Concept and Structure The diagram is essentially an end-oriented or goal-oriented picture of a problem. It is used to organize and graphically display multiple potential causes that result in a single, specific output or effect.

The "6M" Categories To ensure a comprehensive brainstorming session, causes are traditionally grouped into generic hierarchical headings. In construction and industrial engineering, these are commonly referred to as the "6Ms".

Category	Description in the Context of Construction	Examples
Manpower	Issues related to the personnel or workforce involved in the process.	Lack of training, incompetence, fatigue, poor supervision,.
Methods	The techniques, procedures, or technology used to perform the work.	Improper sequencing, faulty method statements, non-compliance with specs,.
Machine	The plant, equipment, and tools required to execute the task.	Broken pumps, uncalibrated tools, inappropriate machinery,.
Material	The raw materials, parts, and consumables used in the product.	Substandard cement, incorrect design mix, damaged supplies,.
Measurement	The instruments, sampling methods, and metrics used to verify quality.	Faulty calibration, incorrect readings, improper testing procedures,.
Mother Nature	The environmental conditions impacting the work site or materials.	Extreme temperature, rain, dust, site constraints,.

Step-by-Step Process for Construction When implementing this tool on a construction project, teams should follow a structured, six-step procedure,,,:

1. Identify the Problem (The Effect): Agree on a clear problem statement. Write it in a box at the center-right of a whiteboard, and draw a horizontal prime arrow pointing to it (forming the fish's spine).
2. Select the Team: Gather an interdisciplinary brainstorming team (e.g., site engineers, foremen, QA/QC inspectors, and laborers) who have direct knowledge of the process.
3. Draw the Prime Arrows: Establish the major categories contributing to the problem. Use the 6M headings (Manpower, Methods, Machine, Material, Measurement, Environment) and draw them as branches angling off the main horizontal arrow.
4. Identify Defect Causes: Brainstorm all possible causes by asking, "Why does this happen?" As ideas are generated, write them as horizontal sub-branches under the appropriate 6M category. (Note: A cause can be placed under multiple categories if it has multiple relationships).
5. Drill Down (The "5 Whys"): Continue to ask "Why?" for each cause identified to generate deeper levels of sub-causes. Focus attention on branches where ideas are sparse to ensure thorough analysis.
6. Identify Corrective Action: Once the root causes are exposed, develop targeted corrective and preventive actions, and analyze their implementation using the same structured logic.

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3. CEM Application Example: Bad Concrete (Compressive Strength Failure)

The Scenario: Imagine you are managing the construction of a high-rise development. Following a major slab pour, the 28-day cylinder tests return from the lab indicating that the concrete failed to meet the specified design compressive strength. In construction, "Bad Concrete" is a critical failure because nonconforming structural work is incredibly difficult to rectify, and sometimes remedial action is impossible without demolition.

Applying the Fishbone Diagram: To avoid finger-pointing between the ready-mix supplier and your site team, you convene a quality circle and map out a Fishbone diagram to identify the root causes,.

• The Effect (Head of the Fish): "Bad Concrete" (Failure to comply with design strength).
• Brainstorming the 6Ms:
  • Manpower: Was the workforce adequately skilled? The team notes that there was incompetent labor vibrating the concrete, and improper supervision by the foreman during the pour,.
  • Method: Was the placement procedure correct? The team identifies improper pouring techniques, noncontinuity in casting (creating cold joints), and insufficient curing time applied to the slab,.
  • Machine: Did the equipment fail? The investigation reveals a malfunctioning vibrator, intermittent breakdowns of the concrete pump, and an inefficient transit mixer,.
  • Material: Were the ingredients compliant? The team scrutinizes the cement quality, the grade of the aggregate, the water source, the dosage of admixtures, and the overall design mix provided by the batch plant,.
  • Measurement: Was the testing accurate? The team questions the calibration of the lab's crushing machine and the slump cones.
  • Mother Nature (Environment): Were external conditions a factor? The team records that the ambient temperature was exceptionally high that day, and the weather was highly dusty and rainy, which may have contaminated the mix.

By laying out this "Bad Concrete" Ishikawa diagram, the project management team transforms a chaotic problem into a structured visual map. They can now methodically test each hypothesis—checking batch plant tickets (Material), reviewing weather logs (Mother Nature), and auditing equipment maintenance records (Machine)—to isolate the exact root cause and prevent it on the next pour.

Fishbone diagram representing the drivers and enablers for a 4D BIM ICSCL

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Bibliography

• https://www.youtube.com/watch?v=DzU8GVVwbcU
• El-Daghar, Khaled. (2017). Performance Improvement Plan in Building Process According to Quality Leaders and Quality Improvement Tools and Techniques. Architecture and Planning Journal (APJ). 24. 67-82. 10.54729/2789-8547.1020.
• https://techqualitypedia.com/7-qc-tools/
• Rumane, A. R. (2010/2018). Quality Management in Construction Projects (1st & 2nd ed.). CRC Press.
• Rumane, A. R. (2013). Quality Tools for Managing Construction Projects. CRC Press.
• Yang, K., & El-Haik, B. (n.d.). Design for Six Sigma. McGraw-Hill.
• Unknown Author (n.d.). Texto.11.ConstructionQuality.