Root Cause Analysis Methodologies

Root Cause Analysis Methodologies

Decision criteria, templates, and implementation guidance for RCA techniques.

Table of Contents

• Method Selection Matrix
• 5 Why Analysis
• Fishbone Diagram
• Fault Tree Analysis
• Human Factors Analysis
• Failure Mode and Effects Analysis
• Selecting the Right Method

Method Selection Matrix

When to Use Each Method

Quick Selection Decision Tree

Is the issue safety-critical or involves system reliability?
├── Yes → Use FAULT TREE ANALYSIS
└── No → Is human error the suspected primary cause?
    ├── Yes → Use HUMAN FACTORS ANALYSIS
    └── No → How many potential contributing factors?
        ├── 1-2 factors → Use 5 WHY ANALYSIS
        ├── 3-6 factors → Use FISHBONE DIAGRAM
        └── Unknown/Many → Use FMEA (proactive) or Fishbone (reactive)

5 Why Analysis

Overview

Simple, iterative technique asking "why" repeatedly (typically 5 times) to drill from symptoms to root cause.

When to Use

• Single-cause issues with linear causation
• Process deviations with clear failure point
• Quick investigations requiring rapid resolution
• Problems where symptoms clearly link to cause

When NOT to Use

• Complex multi-factor problems
• Safety-critical incidents requiring comprehensive analysis
• Issues with multiple interacting causes
• When systemic factors are suspected

5 Why Template

PROBLEM STATEMENT:
[Clear, specific description of what happened, when, where, and impact]

WHY 1: Why did [problem] occur?
BECAUSE: [First-level cause]
EVIDENCE: [Data/observation supporting this cause]

WHY 2: Why did [first-level cause] occur?
BECAUSE: [Second-level cause]
EVIDENCE: [Data/observation supporting this cause]

WHY 3: Why did [second-level cause] occur?
BECAUSE: [Third-level cause]
EVIDENCE: [Data/observation supporting this cause]

WHY 4: Why did [third-level cause] occur?
BECAUSE: [Fourth-level cause]
EVIDENCE: [Data/observation supporting this cause]

WHY 5: Why did [fourth-level cause] occur?
BECAUSE: [Root cause - typically systemic or management system failure]
EVIDENCE: [Data/observation supporting this cause]

ROOT CAUSE VALIDATION:
- [ ] Can the root cause be verified with evidence?
- [ ] If root cause is eliminated, would problem recur?
- [ ] Is the root cause within organizational control?
- [ ] Does the root cause explain all symptoms?

Example: Calibration Overdue

PROBLEM: pH meter (EQ-042) found 2 months overdue for calibration

WHY 1: Why was calibration overdue?
BECAUSE: The equipment was not on the calibration schedule
EVIDENCE: Calibration schedule reviewed, EQ-042 not listed

WHY 2: Why was it not on the calibration schedule?
BECAUSE: The schedule was not updated when equipment was purchased
EVIDENCE: Purchase date 2023-06-15, schedule dated 2023-01-01

WHY 3: Why was the schedule not updated?
BECAUSE: No process requires schedule update at equipment purchase
EVIDENCE: Equipment procedure SOP-EQ-001 reviewed, no such requirement

WHY 4: Why is there no requirement to update the schedule?
BECAUSE: The procedure was written before equipment tracking was centralized
EVIDENCE: SOP-EQ-001 last revised 2019, equipment system implemented 2021

WHY 5: Why has the procedure not been updated?
BECAUSE: Periodic procedure review did not assess compatibility with new systems
EVIDENCE: No documented review of SOP-EQ-001 against new equipment system

ROOT CAUSE: Procedure review process does not assess compatibility
with organizational systems implemented after original procedure creation

Fishbone Diagram

Overview

Also called Ishikawa or cause-and-effect diagram. Organizes potential causes into categories branching from the problem statement.

Standard Categories (6M)

Fishbone Template

PROBLEM STATEMENT: [Effect being investigated]

                    ┌── Man ────────────────┐
                    │  ├─ [Cause 1]         │
                    │  ├─ [Cause 2]         │
                    │  └─ [Cause 3]         │
                    │                       │
┌── Machine ────────┤                       ├── Method ──────────┐
│  ├─ [Cause 1]     │                       │  ├─ [Cause 1]      │
│  ├─ [Cause 2]     │     PROBLEM           │  ├─ [Cause 2]      │
│  └─ [Cause 3]     ├───────────────────────┤  └─ [Cause 3]      │
│                   │                       │                    │
├── Material ───────┤                       ├── Measurement ─────┤
│  ├─ [Cause 1]     │                       │  ├─ [Cause 1]      │
│  ├─ [Cause 2]     │                       │  ├─ [Cause 2]      │
│  └─ [Cause 3]     │                       │  └─ [Cause 3]      │
                    │                       │
                    └── Environment ────────┘
                       ├─ [Cause 1]
                       ├─ [Cause 2]
                       └─ [Cause 3]

CAUSE PRIORITIZATION:
| Cause | Category | Likelihood | Evidence | Priority |
|-------|----------|------------|----------|----------|
| [Cause A] | Method | High | [Evidence] | 1 |
| [Cause B] | Man | Medium | [Evidence] | 2 |

ROOT CAUSES IDENTIFIED:
1. [Primary root cause with supporting evidence]
2. [Contributing cause with supporting evidence]

Facilitation Guidelines

1. Assemble cross-functional team (3-8 people)
2. Define problem statement clearly before starting
3. Brainstorm causes without judgment first
4. Organize into categories after brainstorming
5. Drill down on each major cause (sub-causes)
6. Prioritize based on evidence and likelihood
7. Validate top causes with data

Fault Tree Analysis

Overview

Top-down, deductive analysis starting with undesired event and systematically identifying all potential causes using Boolean logic (AND/OR gates).

When to Use

• Safety-critical system failures
• Complex system reliability analysis
• Events with multiple failure pathways
• Regulatory-required investigations (FDA, MDR)

FTA Symbols

FTA Template

TOP EVENT: [Undesired event under investigation]

LEVEL 1 (Immediate Causes):
[Top Event]
    │
    └── OR GATE ──┬── [Cause 1.1]
                  ├── [Cause 1.2]
                  └── [Cause 1.3]

LEVEL 2 (Contributing Causes):
[Cause 1.1]
    │
    └── AND GATE ──┬── [Cause 2.1]
                   └── [Cause 2.2]

MINIMAL CUT SETS:
(Combinations of basic events that cause top event)
1. {Basic Event A, Basic Event B}  ← Both required (AND)
2. {Basic Event C}  ← Single point failure (OR)
3. {Basic Event D, Basic Event E}  ← Both required (AND)

CRITICAL PATH ANALYSIS:
Most likely failure pathway: [Description]
Single points of failure: [List]

RECOMMENDATIONS:
- Address single points of failure first
- Add redundancy where AND gates show vulnerability
- Prioritize controls on highest probability paths

Cut Set Analysis

Minimal cut sets identify the smallest combination of basic events causing the top event:

• Single-element cut sets: Single points of failure (highest priority)
• Two-element cut sets: Dual failure scenarios
• Probability calculation: P(Top Event) = Union of P(Cut Sets)

Human Factors Analysis

Overview

Systematic analysis of human error focusing on cognitive, physical, and organizational factors contributing to performance failures.

HFACS Categories

Human Factors Analysis and Classification System:

Human Error Types

Human Factors Investigation Template

INCIDENT DESCRIPTION:
[What happened, who was involved, when, where]

UNSAFE ACTS ANALYSIS:
Type of Error: [ ] Slip  [ ] Lapse  [ ] Mistake  [ ] Violation
Description: [Specific action or inaction]
Task Being Performed: [Activity at time of error]
Experience Level: [Novice/Intermediate/Expert]

PRECONDITIONS FOR UNSAFE ACTS:
Cognitive Factors:
- [ ] Task complexity exceeded capability
- [ ] Time pressure
- [ ] Distraction/interruption
- [ ] Mental fatigue

Physical Factors:
- [ ] Physical fatigue
- [ ] Inadequate lighting
- [ ] Noise interference
- [ ] Workspace ergonomics

Team Factors:
- [ ] Communication breakdown
- [ ] Coordination failure
- [ ] Inadequate leadership

SUPERVISORY FACTORS:
- [ ] Inadequate supervision
- [ ] Failed to correct known problem
- [ ] Inappropriate staffing
- [ ] Authorized unnecessary risk

ORGANIZATIONAL FACTORS:
- [ ] Resource management deficiency
- [ ] Organizational process issue
- [ ] Organizational culture/climate

ROOT CAUSE(S):
[Human factors root causes identified]

CORRECTIVE ACTIONS:
| Action | Target Factor | Priority |
|--------|---------------|----------|
| [Action 1] | [Factor addressed] | High |
| [Action 2] | [Factor addressed] | Medium |

Failure Mode and Effects Analysis

Overview

Proactive, systematic technique identifying potential failure modes, their causes, and effects before failures occur.

FMEA Types

Risk Priority Number (RPN)

RPN = Severity (S) × Occurrence (O) × Detection (D)

Severity Scale (1-10):

Occurrence Scale (1-10):

Detection Scale (1-10):

FMEA Template

PROCESS/PRODUCT: [Name]
FMEA TEAM: [Members]
DATE: [Date]

| Item/Step | Failure Mode | Effect | S | Cause | O | Controls | D | RPN | Action |
|-----------|--------------|--------|---|-------|---|----------|---|-----|--------|
| [Item 1] | [How it fails] | [Impact] | 8 | [Why] | 4 | [Current] | 6 | 192 | [Action] |
| [Item 2] | [How it fails] | [Impact] | 6 | [Why] | 3 | [Current] | 4 | 72 | [Action] |

RPN THRESHOLD: Actions required for RPN > [threshold]
HIGH SEVERITY RULE: Actions required for S >= 9 regardless of RPN

ACTION PRIORITIZATION:
1. Address all items with S >= 9 first
2. Address items with highest RPN
3. Focus on reducing Occurrence (prevention)
4. Then improve Detection (inspection)

Selecting the Right Method

Decision Flowchart

START: Investigation Required
    │
    ├── Is this a proactive assessment (no failure yet)?
    │   └── Yes → Use FMEA
    │
    ├── Is the issue safety-critical?
    │   └── Yes → Use FAULT TREE ANALYSIS
    │
    ├── Is human error the primary concern?
    │   └── Yes → Use HUMAN FACTORS ANALYSIS
    │
    ├── Are there multiple contributing factors (3+)?
    │   ├── Yes → Use FISHBONE DIAGRAM
    │   └── No → Use 5 WHY ANALYSIS
    │
    └── Uncertain? → Start with 5 WHY, escalate to FISHBONE if needed

Hybrid Approach

For complex investigations, combine methods:

1. Initial screening: 5 Why for quick cause identification
2. Detailed analysis: Fishbone to explore all categories
3. Validation: Fault Tree for critical failure paths
4. Systemic factors: Human Factors for people-related causes
5. Prevention: FMEA for future risk mitigation

Documentation Requirements