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Question 10 of 20 Fundamentals Practical

How do you use the five whys, and where does it fall short?

Short answer

Start from a precise problem statement, ask why it happened, and keep asking why of each answer until you reach a cause you can act on, checking each step with evidence. It falls short because it follows one causal chain, while most failures have several interacting causes.

Why

The five whys is popular because it is quick and needs no statistics. Each answer becomes the next question, and five is a rule of thumb rather than a requirement. Used well, it pushes a team past the first, comfortable answer such as "the operator made a mistake" toward why the mistake was possible.

Its weakness is structural. It produces a single line of cause and effect, and the line depends on which answer the team chooses at each step. Two teams can reach different root causes from the same event.

Critiques in the patient safety literature argue that root cause analysis tends to produce simple linear narratives for problems that have multiple interacting contributions, and that investigators then settle for weak actions such as reminders. In GMP, EU Chapter 1 accepts that sometimes only the most likely causes can be addressed, which is an admission that a single proven root cause is not always available. The fix is to combine tools.

A cause and effect or fishbone diagram, which ICH Q9(R1) lists among basic risk management methods, maps many possible causes across categories like people, methods, materials, machines, environment and measurement. The five whys can then drill into the branches the evidence supports. Every "because" should be backed by data, or it is a guess.

How to work it through

  1. Write a specific problem statement with what, where, when and how much.
  2. Ask why it happened and record the answer with the evidence that supports it.
  3. Ask why again of that answer, and repeat until you reach a cause that you can control.
  4. Check the chain backwards by asking whether removing each cause would have prevented the effect.
  5. Map other contributing causes with a fishbone diagram so the single chain does not hide them.
  6. Choose actions that target the controllable causes.

An example

Problem: one lot of vials labeled with the wrong expiry date. Why? The printer used the previous lot's data.

Why? The operator did not update the printer job. Why?

The job change step is in a separate screen that is not prompted at lot change. Why? The software was configured without a lot-change interlock.

The team checks evidence at each step, including the printer log. A fishbone also shows that the label inspection camera was set to check barcode only, not expiry text. Actions cover both the interlock and the camera setting, not just retraining.

Where the answer stops holding

Answers depend on who is in the room and what they already believe. The method gives no way to weigh competing branches. It works best for simple, well-bounded problems and poorly for systemic failures.

A strong answer covers

  • Precise problem statement first
  • Evidence for each answer
  • Stop at a controllable cause, not a fixed count
  • Single causal chain is the key weakness
  • Combine with a fishbone or other multi-cause tool

Common mistakes

  • Stopping at operator error as the final why.
  • Treating five as a required number of steps.
  • Choosing each answer by opinion rather than evidence.