4 Root Cause Analysis techniques every quality engineer should know

When problems arise, finding solutions begins with understanding why something went wrong in the first place. For any quality engineer, Root Cause Analysis techniques are the key to effective problem-solving. They offer a structured approach to identify the underlying factors that lead to defects, inefficiencies, or disruptions within supplier quality processes.

In the field of quality engineering, mastering these techniques is essential for preventing recurrence, improving system reliability, ensuring compliance, and driving continuous improvement across the supply chain. Keep reading to learn more.

Why Root Cause Analysis matters in quality engineering 

Root Cause Analysis (RCA) is fundamental in quality engineering because it aims to identify the deepest factors contributing to a problem, rather than merely addressing its symptoms. By uncovering these underlying reasons, RCA achieves lasting improvements and enables the development of permanent solutions, ensuring that efforts are effective and preventing the reoccurrence of issues —which ultimately saves time and resources.

Furthermore, RCA is a critical step within many supplier quality processes, such as Supplier Corrective Action Requests (SCAR). A SCAR is a formal notification requesting a resolution to a supplier about a nonconformance in supplied goods or services. Then, the supplier is expected to conduct a Root Cause Analysis, often using tools like the 5 Whys technique or a Fishbone diagram, and report their findings within the SCAR to ensure that targeted corrective actions address the core problems.

4 Root Cause Analysis techniques you should know 

The 5 Whys technique 

A straightforward, iterative interrogative technique used to explore the cause-and-effect relationships underlying a particular problem. By repeatedly asking “Why?” (typically five times), it helps peel back layers of symptoms to reveal the foundational root cause.

The simplicity of the 5 Whys technique makes it highly effective for quickly investigating less complex issues, often within daily operational contexts, by guiding teams to understand the relationships between problems and their origins.

Fishbone Diagram (Ishikawa) 

Also known as a cause-and-effect diagram, the Fishbone Diagram is a visual tool for systematically identifying and organizing potential causes of a problem. It categorizes causes into major groups (commonly Man, Machine, Material, Method, Measurement, and Environment), resembling the shape of a fish bone.

This structure facilitates comprehensive brainstorming in a team setting, allowing for the mapping of multiple potential cause categories and their contributing factors to a single effect, making it excellent for visualizing complex problem landscapes.

Fault Tree Analysis (FTA) 

A top-down, deductive analytical technique that uses Boolean Logic to model combinations of events that could lead to a specified undesirable outcome (the “top event”). It graphically represents the logical relationships between various system failures, human errors, and external events.

FTA is particularly valuable for analyzing complex systems in industries like aerospace, automotive, and electronics, where understanding the probability and pathways of system failures is critical for safety and reliability.

Pareto Analysis 

Based on the Pareto Principle (the 80/20 rule), this technique helps identify the “vital few” causes that contribute to the “trivial many” problems. It involves collecting and categorizing data on defects or problems, then ranking them from most frequent to least frequent. 

By visually representing this data, typically with a bar chart, Pareto Analysis allows quality engineers to prioritize which issues to address first, focusing resources on the 20% of causes that account for 80% of the problems, maximizing improvement efforts.

When and how to apply each technique best-case scenarios for each tool

Selecting the right root cause analysis technique is crucial for effective problem-solving. Each method has its strengths and is best suited for particular scenarios.

• The 5 Whys technique

Best for simple to moderately complex problems with a clear, linear cause-and-effect chain. It’s ideal for daily operational issues, quick problem-solving, and situations where immediate action is needed. It’s also effective when the problem is directly observable and can be traced back through a series of human actions or simple equipment failures.

How to Apply: State the problem clearly. Define the symptom you’re trying to solve. Ask “Why?” Ask why the problem occurred. Repeat “Why?” For each answer, ask “Why?” again. Continue this process, typically five times, or until you reach a root cause that, if corrected, would prevent the problem from recurring. The final “why” should point to a process or system issue that can be addressed.

• Fishbone Diagram (Ishikawa)

Excellent for complex problems with multiple potential causes across different categories. It’s best used in a team brainstorming environment where diverse perspectives can contribute to identifying all possible contributing factors. Ideal for quality issues where the cause isn’t immediately obvious and could stem from various aspects of a process.

How to apply: Write the problem statement at the head of the fishbone. Draw major bones branching off the spine, representing broad categories of causes. For each one, brainstorm specific causes that might contribute to the problem and draw them as smaller bones branching off the main categories. For each cause, ask “Why?” to identify sub-causes, adding them as even smaller branches. Once complete, review the diagram to identify patterns, recurring issues, and the most likely root causes.

• Fault Tree Analysis (FTA)

Suited for safety-critical systems, complex engineering problems, and scenarios where understanding the logical pathways to failure is paramount. Common in industries like aerospace, automotive, nuclear, and electronics, where the cost of failure is high. It’s typically used for pre-analysis (predicting failures) or post-analysis (investigating failures) of undesired events.

How to apply: Clearly state the undesired event you want to analyze. Determine the immediate, necessary conditions that must exist for the top event to occur. Employ Boolean Logic gates to link causes. Continue breaking down events into more basic, independent events until you reach “basic events” —events that cannot be further broken down. Analyze the fault tree to identify critical paths to failure, calculate probabilities (if data is available), and pinpoint single points of failure.

• Pareto Analysis

Ideal for identifying and prioritizing the most significant problems or causes when a large number of issues are present. It’s particularly useful for focusing improvement efforts on the “vital few” that account for the majority of the impact. Excellent for scoping before diving into deeper root cause analysis.

How to apply: Gather data on the frequency or cost of different problems or causes. Group the data by problem type or cause and count their occurrences. Rank the categories from most frequent (or costly) to least frequent. Calculate the cumulative percentage for each category. Plot the frequencies as bars (descending order) and the cumulative percentages as a line graph. Observe where the cumulative percentage line reaches approximately 80% to identify the few categories responsible for most of the problems.

Streamline supplier quality processes with digital documentation

Effective digital documentation is crucial for centralizing RCA efforts, ensuring traceability, fostering continuous improvement, and facilitating compliance. Streamline and optimize all your supplier quality processes with a centralized digital solution, like Kiuey. 

We provide a comprehensive, cloud-based platform designed specifically to empower quality engineers to effectively manage their supplier ecosystem. Rather than disparate spreadsheets and email chains, Kiuey allows you to:

• Standardize and accelerate PPAP/APQP
• Proactively manage corrective actions
• Enhance supplier audits
• Optimize supplier performance
• Improve incoming inspections
• Gain real-time analytics and insights
• Ensure compliance and transparency

Move beyond reactive problem-solving, and into a more efficient approach with digital quality engineering solutions. Save time to focus on finding the right solution and revolutionize your supplier quality management with Kiuey. Schedule a demo today!