Root Cause Analysis
Published on October 9, 2026
Root Cause Analysis (RCA)
RCA is a structured, systematic process for identifying the underlying (root) causes of an adverse event or near-miss in healthcare. The goal is not to assign blame to an individual but to identify system-level failures that allowed the error to occur, and to design changes that prevent recurrence.
The principle tested most often: RCA focuses on systems, not people. A nurse who administers the wrong medication is not the root cause. The root cause might be look-alike drug packaging, inadequate labeling systems, fatigue from excessive shift hours, or a broken double-check protocol. The exam will present a scenario and ask what the root cause is; the correct answer is always the system factor, never the individual's mistake.
The Fishbone Diagram (Ishikawa Diagram)
The fishbone diagram was developed by Kaoru Ishikawa. It is a visual tool that organizes potential causes of a problem into categories, branching off a central spine like the bones of a fish. The "head" of the fish is the adverse event or problem. Each major bone represents a category of causes, and smaller bones represent contributing factors within that category.
Standard Categories in Healthcare
People (Manpower)
What It Covers
Staff training, competence, communication, fatigue, staffing levels
Example (Wrong-Site Surgery)
Surgeon did not personally mark the operative site; resident was unsupervised
Methods (Procedures)
What It Covers
Protocols, guidelines, checklists, standard operating procedures
Example (Wrong-Site Surgery)
Surgical safety checklist (time-out) was skipped due to time pressure
Materials (Equipment)
What It Covers
Supplies, devices, medications, technology
Example (Wrong-Site Surgery)
Imaging films were displayed in reverse orientation on the lightbox
Machines (Technology)
What It Covers
Equipment function, electronic health records, information systems
Example (Wrong-Site Surgery)
EHR displayed the laterality field in a non-prominent location
Environment
What It Covers
Physical workspace, noise, lighting, interruptions, culture
Example (Wrong-Site Surgery)
Operating room was noisy during the time-out; staff felt unable to speak up
Measurement
What It Covers
Data collection, monitoring, feedback systems
Example (Wrong-Site Surgery)
No audit system existed to track time-out compliance
Category | What It Covers | Example (Wrong-Site Surgery) |
|---|---|---|
People (Manpower) | Staff training, competence, communication, fatigue, staffing levels | Surgeon did not personally mark the operative site; resident was unsupervised |
Methods (Procedures) | Protocols, guidelines, checklists, standard operating procedures | Surgical safety checklist (time-out) was skipped due to time pressure |
Materials (Equipment) | Supplies, devices, medications, technology | Imaging films were displayed in reverse orientation on the lightbox |
Machines (Technology) | Equipment function, electronic health records, information systems | EHR displayed the laterality field in a non-prominent location |
Environment | Physical workspace, noise, lighting, interruptions, culture | Operating room was noisy during the time-out; staff felt unable to speak up |
Measurement | Data collection, monitoring, feedback systems | No audit system existed to track time-out compliance |
Some sources use the mnemonic 6M: Manpower, Methods, Materials, Machines, Milieu (environment), Measurement. Others use a healthcare-adapted version with categories like Patient, Provider, Task, Communication, Environment, Organization.
How to Read It on the Exam
A vignette may present a completed fishbone diagram or describe the process of building one. The question will typically ask:
Which category does a given contributing factor belong to?
What is the root cause versus a contributing factor?
What corrective action addresses the root cause rather than the surface-level error?
Other Tools Used in RCA
The fishbone diagram is not the only RCA tool. The exam may reference these alternatives:
Fishbone (Ishikawa) diagram
How It Works
Categorizes potential causes visually around a central problem
When It Is Used
Brainstorming phase; organizing many possible causes
5 Whys
How It Works
Asks "Why?" repeatedly (typically five times) to drill from the surface event to the root cause
When It Is Used
Simple, linear causal chains; quick analysis
Fault tree analysis
How It Works
Uses Boolean logic (AND/OR gates) to map how combinations of failures lead to an event
When It Is Used
Complex systems where multiple simultaneous failures are required for the event to occur
Failure Mode and Effects Analysis (FMEA)
How It Works
Identifies potential failure modes before they occur, assigns risk priority numbers
When It Is Used
Prospective (proactive) risk assessment, unlike RCA which is retrospective
Pareto chart
How It Works
Bar chart ranking causes by frequency; applies the 80/20 rule
When It Is Used
Prioritizing which causes to address first
Process mapping / flowchart
How It Works
Diagrams each step in a process to identify where breakdowns occur
When It Is Used
Understanding workflow and identifying vulnerable steps
Tool | How It Works | When It Is Used |
|---|---|---|
Fishbone (Ishikawa) diagram | Categorizes potential causes visually around a central problem | Brainstorming phase; organizing many possible causes |
5 Whys | Asks "Why?" repeatedly (typically five times) to drill from the surface event to the root cause | Simple, linear causal chains; quick analysis |
Fault tree analysis | Uses Boolean logic (AND/OR gates) to map how combinations of failures lead to an event | Complex systems where multiple simultaneous failures are required for the event to occur |
Failure Mode and Effects Analysis (FMEA) | Identifies potential failure modes before they occur, assigns risk priority numbers | Prospective (proactive) risk assessment, unlike RCA which is retrospective |
Pareto chart | Bar chart ranking causes by frequency; applies the 80/20 rule | Prioritizing which causes to address first |
Process mapping / flowchart | Diagrams each step in a process to identify where breakdowns occur | Understanding workflow and identifying vulnerable steps |
RCA vs. FMEA: A High-Yield Distinction
Timing
RCA
Reactive (after an event has occurred)
FMEA
Proactive (before an event occurs)
Trigger
RCA
A sentinel event or adverse outcome
FMEA
A new process, a high-risk process, or a system redesign
Goal
RCA
Find out why it happened and prevent recurrence
FMEA
Find out what could go wrong and prevent it from ever happening
Output
RCA
Corrective action plan
FMEA
Risk priority ranking and preventive action plan
Feature | RCA | FMEA |
|---|---|---|
Timing | Reactive (after an event has occurred) | Proactive (before an event occurs) |
Trigger | A sentinel event or adverse outcome | A new process, a high-risk process, or a system redesign |
Goal | Find out why it happened and prevent recurrence | Find out what could go wrong and prevent it from ever happening |
Output | Corrective action plan | Risk priority ranking and preventive action plan |
05Whys: A Quick Example
Problem: A patient received the wrong dose of anticoagulant.
Why? The nurse administered 10 mg instead of 1 mg.
Why? The nurse read the order as "10" because the decimal point was missing.
Why? The prescriber wrote "1.0 mg" and the decimal point was unclear on the handwritten order.
Why? The institution still permitted handwritten medication orders in certain units.
Why? The hospital had not completed its transition to computerized physician order entry (CPOE) in all departments.
Root cause: Incomplete implementation of CPOE, combined with a policy that still permitted handwritten orders.
Notice how the root cause is a system failure, not "the nurse misread the order." The corrective action targets the system: complete the CPOE rollout and eliminate handwritten orders.
Where RCA Fits in the Quality Improvement Landscape
Concept | Relationship to RCA |
|---|---|
Patient safety | RCA is a core patient safety methodology, typically mandated after sentinel events |
Sentinel event | A sentinel event (unexpected death, wrong-site surgery, serious harm) triggers an RCA |
Swiss Cheese Model (James Reason) | The theoretical basis for RCA; errors occur when holes in multiple defense layers align simultaneously |
Just Culture | The organizational philosophy that supports RCA; distinguishes between human error (system issue), at-risk behavior (coaching), and reckless behavior (accountability) |
PDSA Cycle | The corrective actions identified by RCA are often implemented and tested using Plan-Do-Study-Act cycles |
Traps and High-Yield Pearls
The most common trap is selecting a person-level cause as the root cause when a system-level cause is available. If a pharmacist dispensed the wrong drug because two medications were stored next to each other in look-alike packaging, the root cause is the storage system and packaging, not the pharmacist's inattention.
A second trap is confusing RCA (reactive) with FMEA (proactive). If the event has already happened, you perform RCA. If you are designing or redesigning a system and want to prevent future errors, you perform FMEA. The temporal direction of the analysis is the discriminator.
A third point: the fishbone diagram is a brainstorming and organizing tool, not the analysis itself. Building a fishbone diagram does not complete an RCA. The RCA is complete only when the team has identified the root cause, developed a corrective action plan, and established a monitoring system to verify that the corrective action works. The fishbone is a step in the process, not the conclusion.