 |
Making the system stable |
| Step Three |
Control
charts and reducing variation
We know that our system is a network of interdependent processes. Now we need to be able to answer these questions:
How do processes behave?
How can the behavior of a process influence our system’s behavior?
What actions should we take to continuously improve our system?
The essential requirement for managing
a system is the ability to predict. However, systems are unstable
by their very nature , i.e. they produce unpredictable results. If we want
to have control over our actions, then our system must be stable.
Control charts and reducing variation
Control charts
were devised to measure and improve the variation of a system. A control
chart describes the way a process behaves. It allows us to measure
the degree of stability of the process.
We need to know if a process is in control
or not, i.e. what kind of variation is affecting it. Variation in a process
can be of two kinds:
Controlled variation which is stable and consistent over time, due to common
causes, i.e. causes intrinsic to the process and therefore predictable
Uncontrolled variation which is not consistent over time, due to special
causes i.e. causes external to the process itself. It seriously undermines
a manager’s ability to predict, and therefore his capacity to manage.
We can measure and improve the stability
of our system by applying control charts to the main processes of our system
that we have previously flowcharted.
We achieve Quality and the continuous
improvement of our system’s processes by constantly reducing the sources
of variation that undermine the predictability of our processes. It is
not sufficient to satisfy customer specifications. This alone does not
allow us to understand the reliability and repeatability of our processes.
We can give the customer 100% of what he wants operating a process which
is unstable.
A state of control is not a natural state
for a process, and entropy does exist. If we cannot predict the outcome
of a process, we cannot manage it.
Summary
Maximum Quality is the result of minimum
variation in processes. The processes which make up a system or organization
are interdependent. If we do not understand the variation of processes,
we cannot know what impact our efforts to improve a performance might have
elsewhere. For this reason the goal of Step Three
is to achieve a stable system. Only when we achieve stability can we truly
focus on improving the system’s performance and increasing its Throughput.
