Only after we have the data to allow us to understand what is happening can we start to find out why. This is where the quality professional can open his or her toolbox and unleash (or sometimes, it seems, inflict) the darker reaches of SPC on the team. This is now the time to roll out Ishikawa fishbone (cause and effect) diagrams, 5Whys, Pareto charts, histograms, scatter plots… the list is seemingly endless.
I listed fishbone diagrams and 5Whys first because they’re two tools that are often helpful here. There are many excellent textbooks, websites and courses that will give all anyone needs on the whole range of tools and how to use them. This is the time when the consummate professional shows the benefit of a sound quality education by being able to choose tools to fit the situation, rather than find ways to use the tool picked up on the latest training course.
However, I’m not going to dwell on the tools themselves, rather what we want to use them for. We’ve gathered copious amounts of data which we now dig through to find out why we have the problem – without doing that, all our efforts gathering data were wasted. There may be more than one factor contributing to the problem but it’s usually possible to delve deeper to find a single common factor (or, at worst, a very small number) – the root cause.
As before, be careful to complete this step before moving on – without fully understanding the problem and knowing the root cause, any solution we devise may not be the best (it may not even be right and end up making the situation worse). But, having got to this point, we now know (or should know) what the real problem is.