Interrelationship Digraph
An Interrelationship Digraph (also called Digraph or Network Diagram) is a sophisticated problem-solving tool used during the Lean Six Sigma Define Phase to map complex cause-and-effect relationships among multiple variables, problems, or factors. This tool extends beyond simple fishbone diagrams b… An Interrelationship Digraph (also called Digraph or Network Diagram) is a sophisticated problem-solving tool used during the Lean Six Sigma Define Phase to map complex cause-and-effect relationships among multiple variables, problems, or factors. This tool extends beyond simple fishbone diagrams by showing how different elements influence one another in a network structure. In the Define Phase, the Interrelationship Digraph helps Black Belts identify root causes and understand process dynamics by visually representing direct and indirect relationships between problem factors. The tool uses arrows to indicate directional relationships, showing which factors are drivers (causes) and which are outcomes (effects). The construction process involves: listing all relevant factors or problems on cards, arranging them in a circle, then drawing arrows between related items to show cause-and-effect connections. Each arrow originates from the cause and points toward the effect. Key benefits include identifying root causes by counting arrows - factors with more outgoing arrows are primary drivers, while those with more incoming arrows are effects. This helps prioritize improvement efforts on high-leverage factors. The tool also reveals critical factors that influence multiple downstream processes, enabling more strategic intervention points. The Interrelationship Digraph is particularly valuable when dealing with complex, multifaceted problems where traditional linear thinking fails. It accommodates multiple feedback loops and circular dependencies common in real business processes. This systems-thinking approach helps Black Belts avoid treating symptoms while missing actual root causes. By visually mapping these relationships, teams gain consensus on problem dynamics, improve communication about process complexity, and make data-driven decisions about where to focus improvement resources. This positions the project for more effective analysis phases and increases the likelihood of sustainable solutions that address true root causes rather than superficial symptoms.
Interrelationship Digraph: Complete Guide for Six Sigma Black Belt Define Phase
Understanding Interrelationship Digraph
What is an Interrelationship Digraph?
An Interrelationship Digraph (ID), also known as a Digraph or Network Diagram, is a quality management tool used to identify and display relationships among various factors, variables, or issues related to a problem. It maps the cause-and-effect relationships between different elements to determine which factors have the most influence on others.
Why is it Important?
The Interrelationship Digraph is critical in Six Sigma and process improvement because:
- Root Cause Analysis: It helps identify the fundamental causes of problems by showing direct and indirect relationships
- Problem Prioritization: It reveals which factors drive the most impact, allowing teams to focus on high-leverage improvement areas
- Complexity Management: When dealing with multiple interconnected issues, the ID provides clarity on which factors are drivers versus outcomes
- Stakeholder Communication: Visual representation makes complex relationships easier to understand and discuss
- Strategic Planning: It helps teams understand the ripple effects of addressing specific issues
How Does an Interrelationship Digraph Work?
The Basic Process:
- List All Relevant Factors: Start by identifying and listing all factors, problems, issues, or variables related to the situation. These become the nodes in your digraph.
- Create a Matrix: Arrange the factors in both rows and columns to create a matrix format (similar to a Cause-and-Effect matrix).
- Identify Relationships: For each pair of factors, ask: Does Factor A influence Factor B? Mark with an arrow (→) indicating the direction of influence.
- Count Arrows:
- Outgoing Arrows (Drivers): Count how many times each factor influences others. High outgoing arrows indicate a factor is a driver.
- Incoming Arrows (Outcomes): Count how many times each factor is influenced by others. High incoming arrows indicate a factor is an outcome or result.
- Analyze Results: Factors with high outgoing arrows are root causes or drivers. Factors with high incoming arrows are effects or symptoms.
Step-by-Step Construction Example:
Suppose a manufacturing team is addressing product defects. They identify these factors:
- Machine Calibration
- Operator Training
- Raw Material Quality
- Environmental Temperature
- Product Defects
They then ask for each pair:
- Does Machine Calibration affect Operator Training? No
- Does Machine Calibration affect Raw Material Quality? No
- Does Machine Calibration affect Environmental Temperature? No
- Does Machine Calibration affect Product Defects? Yes (→)
- Does Operator Training affect Raw Material Quality? No
- Does Operator Training affect Environmental Temperature? No
- Does Operator Training affect Product Defects? Yes (→)
- Does Raw Material Quality affect Environmental Temperature? No
- Does Raw Material Quality affect Product Defects? Yes (→)
- Does Environmental Temperature affect Product Defects? Yes (→)
Final Count:
- Machine Calibration: 1 outgoing arrow (driver)
- Operator Training: 1 outgoing arrow (driver)
- Raw Material Quality: 1 outgoing arrow (driver)
- Environmental Temperature: 1 outgoing arrow (driver)
- Product Defects: 4 incoming arrows (outcome/effect)
Key Advantages of Interrelationship Digraph:
- Identifies secondary causes that might be overlooked
- Shows both direct and indirect relationships
- Distinguishes between root causes and symptoms
- Helps prioritize improvement efforts on high-impact factors
- Encourages system thinking and holistic problem analysis
When to Use an Interrelationship Digraph:
- During the Define phase to understand problem scope
- When multiple interconnected factors contribute to a problem
- During root cause analysis sessions
- To validate hypotheses about cause-and-effect relationships
- When prioritizing which process improvements to implement first
Exam Tips: Answering Questions on Interrelationship Digraph
1. Understand the Terminology
- Driver (Root Cause): Factors with high outgoing arrows; these cause other problems
- Outcome (Effect/Symptom): Factors with high incoming arrows; these result from other factors
- Secondary Driver: Factors with both incoming and outgoing arrows; they are influenced by other factors but also influence outcomes
- Independent Factor: Factors with no or few connections; often not central to the main issue
2. Common Exam Question Types
Question Type 1: Identifying Drivers vs. Outcomes
Example: In an Interrelationship Digraph, which factor would you prioritize for improvement if it has 7 outgoing arrows and 1 incoming arrow?
Answer Strategy: This factor is a strong driver (root cause). Prioritize addressing this first because it influences many other factors. High outgoing arrows indicate root cause potential.
Question Type 2: Interpreting Digraph Results
Example: An ID shows that 'Inadequate Training' has 6 outgoing arrows pointing to various process problems. What does this tell you?
Answer Strategy: This indicates that inadequate training is a root cause affecting multiple outcomes. Implementing training improvements would likely have cascading positive effects on multiple process problems.
Question Type 3: Construction and Logic
Example: When constructing an Interrelationship Digraph, you should ask: Does Factor A influence Factor B? What does a 'Yes' answer result in?
Answer Strategy: A 'Yes' answer means you draw an arrow FROM Factor A TO Factor B, indicating that A influences B. This arrow contributes to A's outgoing count.
Question Type 4: Problem-Solving Application
Example: A team identifies that customer complaints have 8 incoming arrows but only 1 outgoing arrow in their ID. What should they do?
Answer Strategy: Customer complaints are an outcome/effect rather than a root cause. The team should focus on the factors pointing TO complaints (incoming arrows) rather than trying to directly fix complaints.
3. Exam Strategy Tips
- Recognize the Purpose: Remember that IDs are used to distinguish root causes from symptoms. Exam questions often test whether you can identify which is which.
- Arrow Direction Matters: Pay careful attention to arrow direction. The direction shows causality, not just correlation. Arrows point FROM the cause TO the effect.
- Count Carefully: In exam scenarios where you need to analyze an ID, count outgoing arrows (drivers) and incoming arrows (outcomes) systematically.
- Apply the 80/20 Rule: Usually, a few factors (20%) have the most outgoing arrows (are responsible for 80% of the problems). Focus exam answers on identifying these key drivers.
- Think About Sequencing: Exam questions may ask about the order of implementing improvements. Root causes (high outgoing) should typically be addressed before secondary drivers.
4. Common Mistakes to Avoid
- Confusing Direction: Don't draw arrows pointing in the wrong direction. The arrow should point FROM cause TO effect.
- Counting Wrong: Don't confuse incoming and outgoing arrows. Remember: Outgoing = Driver, Incoming = Outcome.
- Over-Complicating: Don't create relationships that don't exist. Only show direct cause-and-effect relationships.
- Ignoring Secondary Drivers: Don't focus only on factors with zero incoming arrows. Secondary drivers (with some incoming arrows) are also important.
- Forgetting the Goal: Remember the ID's purpose is prioritization. Exam answers should demonstrate understanding that high-outgoing-arrow factors deserve priority attention.
5. Practice Exam Scenarios
Scenario 1: In a software development process, an ID shows: Bug Reporting System has 0 incoming arrows and 6 outgoing arrows. What does this indicate?
Correct Answer: The Bug Reporting System is a root driver. Issues with this system cascade throughout the development process. Improving this system would likely resolve many downstream problems.
Scenario 2: An Interrelationship Digraph for hospital wait times shows 'Patient Dissatisfaction' with 5 incoming arrows and 0 outgoing arrows. What should hospital leadership focus on?
Correct Answer: Don't try to directly reduce patient dissatisfaction. Instead, address the 5 factors causing it. Fixing those root causes will naturally reduce dissatisfaction.
Scenario 3: When constructing an ID for supplier quality issues, should you include 'Market Demand' if it doesn't directly relate to quality problems?
Correct Answer: Only include factors relevant to the specific problem being analyzed. Market Demand might be included in a different analysis but probably shouldn't be in a supplier quality ID unless it demonstrably affects quality.
6. Time Management During Exam
- For multiple-choice questions about IDs, focus on identifying the pattern (arrows direction and count) rather than re-analyzing the entire diagram.
- If asked to construct or analyze an ID during the exam, use a systematic approach: list factors, create rows/columns, identify relationships, count arrows, draw conclusions.
- For scenario-based questions, quickly identify the key factor mentioned (high outgoing or incoming arrows) and select the answer that demonstrates proper prioritization.
7. Integration with Other Tools
Exam questions may connect IDs with other Six Sigma tools:
- With Fishbone Diagrams: A Fishbone organizes causes by category; an ID prioritizes which causes matter most
- With Pareto Charts: The critical drivers identified in an ID often become the focus factors for Pareto analysis
- With Process Mapping: An ID might help determine which process steps to examine most closely during mapping
- With Root Cause Analysis: An ID is part of the RCA toolkit to systematically identify root causes
Key Takeaways for Exam Success:
- Interrelationship Digraphs identify root causes by counting arrows (outgoing = driver, incoming = outcome)
- The primary exam focus is distinguishing drivers from outcomes and understanding prioritization
- Arrow direction is critical; always draw FROM cause TO effect
- Root causes (high outgoing arrows) should be addressed before secondary factors
- The tool helps move beyond symptoms to identify what truly drives the problem
- Practice counting arrows systematically to avoid calculation errors under exam pressure
🎓 Unlock Premium Access
Lean Six Sigma Black Belt + ALL Certifications
- 🎓 Access to ALL Certifications: Study for any certification on our platform with one subscription
- 6176 Superior-grade Lean Six Sigma Black Belt practice questions
- Unlimited practice tests across all certifications
- Detailed explanations for every question
- CSSBB: 5 full exams plus all other certification exams
- 100% Satisfaction Guaranteed: Full refund if unsatisfied
- Risk-Free: 7-day free trial with all premium features!