This method is a completely new, unique approach in the principles of finding cause and problem solving, abandoning the traditional approach of starting with theories or possible causes. Instead, start with the facts of the symptoms and make deductions from these to find the cause. This avoids generating dozens of possibilities, which can become unmanageable. It has been proven at Rolls-Royce to get to the root cause much more quickly than with old methods, which can lead to wrong conclusions as to cause and resulting in having to start all over again. This is an evidence-based approach with proven results.
Conventionally, cause is found by generating possible causes and then testing them to establish the actual cause. Many different tools are used to do this (e.g. Fishbone/Ishikawa diagram) but they all involve generating possible causes. Often this approach generates many, many possible causes all of which have to be tested. This can massively extend time to find cause and can lead to confusion. It can also be de-motivating for the people involved.
The alternative is to start with detail facts about the problem and its symptoms. These can be entered row by row onto a simple excel spreadsheet. For each symptom, where or when the symptom occurs is captured - the bad. Also where or when the symptom does not occur - the good. Then the investigation looks for what is different. Deductions are made about the cause. Analogously, each deduction from each detail symptom produces a piece of the jigsaw. The deductions from all the symptoms on all the rows of the spreadsheet are pieced together, like completing a jigsaw, to create a full picture of the root cause.
Simon pioneered this alternative approach based only on experience. This alternative approach has not come from text books or abstract thinking.
There are quite a number of examples where the approach involving starting with possible causes was initially used, then abandoned due to becoming unmanageable. The alternative approach of starting with facts was then used. From this experience, it can be very conservatively estimated that the new, alternative approach takes 50% less time.
For one problem, possible causes were generated using a Fishbone diagram. There was some confusion because of the number of possible causes. Nonetheless, one cause was selected and a corresponding solution put in place. Only when the customer complained loudly that the solution did not work and the problem had re-occurred did the team realise that what they thought was the cause was not the actual cause. Again, a cause was selected and a solution put in place. It didn't work and again the customer complained, this time very loudly.
The alternative approach of starting with facts and deducing from each of them was then adopted. In much less than half the time already spent on the problem the cause was deduced and a solution put in place. Years later the solution has still prevented re-occurrence. So, as well as reduced time, experience of the 'starting with facts' approach has shown it to provide much greater confidence regarding what the cause is and therefore robust solutions.
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You may well have heard of the 5 Whys. How does this fit with this new approach? On the internet one can see the suggestion of asking Why? five times to get to root cause. Asking Why repeatedly is key to getting to root cause - defined as that when eliminated will prevent re-occurrence of the symptom. However, what happens if you ask Why? and you don't know the answer. This is the harsh reality of nearly all the investigations that I have led. Any method to find root cause needs to deal with this reality. It needs to cope with that awful brick wall that you hit in trying to find cause when you ask Why? and the honest answer is simply 'I don't know'. This is a key point. In this scenario, asking Why five times is unproductive.
So what to do when that 'I don't know' brick wall is hit? The method outlined here is applied - that is, gather all the facts about what happened, looking for difference between where/when the problem happened and where/when it did not happen to deduce factually the answer to the question Why? Having established the answer to the first Why? the next step is to ask Why? again and repeat the process just given above to establish the answer to the second Why? Then the process is repeated again.
When to stop asking Why? When you have drilled down to a cause that will, when eliminated/corrected, stop the problem happening again. A simple example to explain - My bicycle tyre has a puncture. Why? I have checked the inner tube and is has a hole in it. If, let's say I then replace the inner tube, the problem will occur again in this scenario. How is that? Because if I ask a second why, that is, why the inner tube has a hole in it, the answer here is because there is a thorn in the outer tyre. So asking why once and just replacing the inner tube will not stop the problem happening again. Asking why a second time and replacing the inner tube and removing the thorn gives a more robust solution. (One could of course continue by asking why was there a thorn in the outer tyre, and so on.)
In summary 5 Whys are not at all effective on their own because you hit the 'I don't know' brick wall. But when used in conjunction with the evidence first root cause analysis approach, 5 Whys is vital to drill down to root cause. Of course, it might be only three Whys or it could be ten Whys, depending on the nature of the problem.
The problem. The cause. What's the difference? The problem is WHAT happened. The cause is WHY it happened. In the tragic Concorde crash of July 2000 near Paris, the crash was the problem. It was caused when one of Concorde's tyres hit a strip which was dropped on the runway by the aircraft that took off immediately prior to Concorde. The strip fell off because of an error in maintenance which was done in America. So the problem was near Paris, the root cause was in America. This example stresses that the problem (what happened) and the cause (why it happened) are distinct.
Why find the cause?
The ultimate goal in resolving a problem is to implement a solution that prevents re-occurrence. Jumping to solution is a well recognised poor approach but why?
Eliminating a problem involves eliminating the cause. And it's the solution's purpose to eliminate the cause. So, simply, before applying a solution, it is necessary to know the cause. The solution first needs to know what it has to eliminate.