claude-skills-reference/ra-qm-team/capa-officer/references/rca-methodologies.md

Root Cause Analysis Methodologies

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

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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

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Method Selection Matrix

When to Use Each Method

Method	Use When	Problem Type	Team Size	Time Required
5 Why	Single-cause issues, process deviations	Linear causation	1-3 people	30-60 min
Fishbone	Multi-factor problems, 3-6 contributing factors	Complex, systemic	3-8 people	2-4 hours
Fault Tree	Safety-critical failures, reliability issues	System failures	2-5 people	4-8 hours
Human Factors	Procedure/training-related issues	Human error	3-6 people	2-4 hours
FMEA	Systematic risk assessment, design review	Potential failures	4-10 people	8-16 hours

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)

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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

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Fishbone Diagram

Overview

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

Standard Categories (6M)

Category	Focus Areas	Typical Causes
Man (People)	Training, competency, workload	Skill gaps, fatigue, communication
Machine (Equipment)	Calibration, maintenance, age	Wear, malfunction, inadequate capacity
Method (Process)	Procedures, work instructions	Unclear steps, missing controls
Material	Specifications, suppliers, storage	Out-of-spec, degradation, contamination
Measurement	Calibration, methods, interpretation	Instrument error, wrong method
Mother Nature (Environment)	Temperature, humidity, cleanliness	Environmental excursions

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

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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

Symbol	Name	Meaning
Rectangle	Top Event / Intermediate Event	Undesired event or intermediate fault
Circle	Basic Event	Primary fault requiring no further analysis
Diamond	Undeveloped Event	Event not fully analyzed (data limitation)
AND Gate	Requires all inputs	All child events must occur for parent
OR Gate	Requires any input	Any child event causes parent

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)

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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:

Level	Category	Examples
Unsafe Acts	Errors, violations	Skill-based, decision, perceptual errors
Preconditions	Conditions for unsafe acts	Fatigue, mental state, CRM, physical environment
Unsafe Supervision	Supervisory failures	Inadequate supervision, planned inappropriate ops
Organizational Influences	Organizational failures	Resource management, organizational climate

Human Error Types

Type	Description	Example	Mitigation
Slip	Execution error in routine task	Wrong button pressed	Error-proofing, forcing functions
Lapse	Memory failure	Forgot step in procedure	Checklists, reminders
Mistake	Planning/decision error	Wrong procedure selected	Training, decision aids
Violation	Intentional deviation	Skipped step to save time	Culture change, supervision

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 |

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Failure Mode and Effects Analysis

Overview

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

FMEA Types

Type	Application	Scope
Design FMEA (DFMEA)	Product design	Component and system design failures
Process FMEA (PFMEA)	Manufacturing process	Process step failures
System FMEA	System-level analysis	System interaction failures

Risk Priority Number (RPN)

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

Severity Scale (1-10):

Rating	Effect	Criteria
10	Hazardous	Failure affects safe operation, no warning
8-9	Very High	Primary function lost, high impact
6-7	High	Performance degraded, customer dissatisfied
4-5	Moderate	Some performance loss, moderate impact
2-3	Low	Minor effect, slight inconvenience
1	None	No discernible effect

Occurrence Scale (1-10):

Rating	Likelihood	Failure Rate
10	Very High	>1 in 10
7-9	High	1 in 20 - 1 in 100
4-6	Moderate	1 in 400 - 1 in 2,000
2-3	Low	1 in 15,000 - 1 in 150,000
1	Remote	<1 in 1,500,000

Detection Scale (1-10):

Rating	Detection	Criteria
10	Absolute Uncertainty	No inspection/control, defect will reach customer
7-9	Very Remote to Remote	Controls unlikely to detect
4-6	Moderate	Controls may detect
2-3	High	Controls likely to detect
1	Almost Certain	Controls will almost certainly detect

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)

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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

Method	Required Outputs	Retention
5 Why	Completed template with evidence	CAPA record
Fishbone	Diagram + prioritized causes	CAPA record
Fault Tree	FTA diagram + cut set analysis	DHF/CAPA record
Human Factors	HFACS analysis + actions	CAPA record
FMEA	FMEA worksheet + action tracking	Design file