Root cause analysis

What it means

Root cause analysis is an approach that, faced with a problem, asks not who caused it but why it could happen. The aim is to find the cause whose removal stops the problem recurring, rather than just fixing its latest symptom.

The simplest method is the five whys: every answer is met with another why until we reach something that can be changed in the process. For more complex problems a fishbone diagram is used, sorting possible causes by people, methods, machines, materials and environment.

The method is part of approaches such as lean and Six Sigma and forms the check step of the PDCA cycle. It needs no software and no consultant, only the willingness to look for the cause in the process rather than in people.

How it works in practice

In bookkeeping we use it when an error keeps recurring, for example when invoices from the same supplier arrive with the wrong supply date or VAT differences appear month after month. A one-off correcting entry fixes a month; root cause analysis fixes the years that follow.

A typical example: an invoice does not match in the control statement. Why? It was booked in a different month. Why? It arrived late. Why? The supplier sends it to an old address. The fix is not another correction but a changed contact and a new rule in internal control.

The outcome is worth writing into a procedure so that the new practice does not leave with the person. At clients this is how simple working instructions, SOPs, and changes to the process map come about that stop the error from coming back.

What to watch out for

The most common mistake is stopping at a person: the accountant made a slip, the storekeeper forgot. People always make mistakes; the question is why the process let the mistake happen and why nobody caught it. As long as the answer ends in a name, the cause stays in the system.

The second mistake is analysing everything. Analysis takes time, so it pays off for errors that recur or are expensive, while a one-off typo just needs correcting. Priorities come from an overview of where most corrections arise and from finding the bottleneck in the process.