What does “Five whys” mean?
Short answer
Five whys is a way to find a root cause. Ask why a problem happened, then why again for each answer, until you reach a cause you can fix.
Also known as: 5 whys, five whys analysis
How it works
IHI puts it simply: when a problem shows up, ask why five times until you reach the root cause.
IHI warns that what we think is the cause may be only another symptom, that there may be more than one root cause, and that different people give different answers.
Example: an infusion pump alarm went unanswered.
- Why 1The alarm volume was set too low.
- Why 2Pumps return to low volume after each reset.
- Why 3No one changed the default after the last software update.
- Why 4No one owns pump setup after updates.
- Why 5The biomedical update checklist has no step for alarm settings. Fix the checklist, set a standard default and assign an owner.
Limits
OSHA makes the same point about investigations: do not stop when you decide a worker made an error. Ask whether the worker had the right tools, time, training and supervision. A chain that ends at a person has stopped too early.
Five is a guide, not a rule. Stop when you reach a cause that a system change can fix. For serious events, IHI points to its RCA2 tool for more rigor.
See five whys, fishbone and fault tree compared. In IncidentKit, investigations record contributing factors, five whys and the final disposition, and a person reviews and signs.
Frequently asked questions
Do you always need exactly five whys?
No. Five is a rule of thumb. Keep asking until you reach a cause you can fix with a change in process, equipment or design. That may take three questions or seven.
Is five whys enough for a sentinel event?
Usually not alone. It follows one chain of cause, and serious events often have several. The Joint Commission expects a full analysis. IHI recommends RCA2 for more rigor.
What is the difference between five whys and a fishbone diagram?
Five whys drills down one chain of cause. A fishbone spreads out many possible causes at once. Teams often use both.
Sources
- IHI: 5 Whys, finding the root cause
- VHA National Center for Patient Safety: Root cause analysis (page and Guide to Performing a Root Cause Analysis, rev. 02/05/2021)
- OSHA: Recommended practices, hazard identification and assessment (incident investigation)
- Joint Commission: Sentinel Event Policy (SE chapter), Comprehensive Accreditation Manual, Update 1, July 2026
Reviewed against the sources above on Oct 5, 2026. Rules change: confirm current requirements with the issuing body or your counsel before relying on any summary.
Put the definition to work.
IncidentKit turns these terms into workflow: reports, investigations, corrective actions and packets.