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To understand variability and
why it is a problem there is a simple tabletop game to play that is a great introduction
to the variability within processes.
In Figure 1.1 two lines are
drawn crossing at 90o with a 2mm circle drawn around their intersection.
The game is to sit at a table and drop a pen into the two millimetre diameter circle from
a height of around 300 mm (one foot). Getting a hit within the circle is the outcome
required from this ‘process’. Repeat the targeting and drop process at
least thirty times. After each drop measure the position of the new mark to an
accuracy of half a millimetre. Record the horizontal distance from the vertical line
(the ‘x’ distance) and the vertical distance from the horizontal line (the
‘y’ distance) in a table like that of Table 1.1.
Observe the average and
spread, of the ‘X’ and ‘Y’ results.
In Table 1.1 no hits are within the two millimetre circle; some are on or
near the edge while most are well away. Even
though great effort was made to control the ‘process’, the results were across a
wide band of outcomes. This same problem
occurs in all business and operations processes. The
outcomes of a process are spread across a range of results.
That is variability. Variability becomes a problem for a business when the results
from a process are not consistently within their required boundaries. If the aim of the game is to
have every pen-drop fall inside the 2mm circle, then we have a very poor process for
achieving that outcome. To get better results
requires changing the process. The game can be
repeated using a different process. The
results in Table 1.2 were from a process where the pen was dropped after aiming it at the
circle from above, much like dropping a bomb from an aeroplane using targeting sights.
The
results of the second attempt to play the cross-hair game using a modified process are
better; the ‘Y’ values are virtually the same as the ‘X’. The averages of the modified process indicate that
the hits were closer to the intersection than those of the first process. There was less spread. But the second process is still not suitable for
meeting the requirements of consistently getting the pen within the circle from a height
of 300mm. It is very unlikely that any process
using human hands to drop a pen within a two mm circle can be controlled sufficiently
accurately. If the requirement is to be met it
will not be done by dropping the pen with human hands. To
get the pen consistently within the circle requires the creation of a process that removes
the variability caused by the human hand. A
number of devices have been proposed. These
include a long, tapered funnel to guide the pen onto the target, a vee-shaped slide to
direct the pen into the circle and a robot with a steady manipulator to drop the pen. One
answer that was jokingly suggested was to open the circle up to 50mm diameter and then
everything will be on target. The suggestion
totally defeats the purpose of having a process that delivers accurate results. But unfortunately it is the solution that many
businesses select. They chose to ‘widen
the target’ and accept any result, good, mediocre or disastrous, rather than improve
their processes. A business that does not
purse excellence in their activities will not last. Examples
of processes with inherent high variability are those that at some point: ·
require
decisions ·
require
choices ·
are
done without exacting training ·
have
no standards ·
have
inadequate procedures ·
lack
correct information ·
are
based on opinion ·
involve
emotion ·
have
multiple ways it can be done ·
are
not measured ·
have
high rates of equipment failure ·
involve
interpretation of data When
such situations arise in a process the chance of variability rises because the process
contains varying degrees of randomness and uncertainty.
Ill-defined, inexact processes and those with poor monitoring and control
are at risk of being impacted badly by any change in performance of their critical success
factors. This is particularly the case in sales and
marketing, finance, human resources, administration, engineering, design, customer
service, production, manufacturing, dispatch, after-sales service and maintenance. Variability can be identified in processes by charting or
graphing process parameters and process outputs over a period of time. Such charts are called ‘run charts’ and
are used to locate the times that the process did not produce the required result. If
you want immediate control over a process then track the process variables, those factors
that influence the result, in real-time so they are observed as they change. If the change is bad you have time to react and
correct it before too much damage is done. If
you want pre-emptive control of a process then trend the variables of the process inputs
before they enter the process. By being sure
that the inputs into a process are correct and right you can be more certain that the
process they feed into will be better behaved. If
you only want to know how well a process performed then monitor its final output, the
product from the process. Unfortunately
monitoring the final output puts you into the position of asking ‘what happened’
when something goes wrong. Just like the
company in Example 1.1 who had no idea what had changed to cause a spate of raw material
stock-outs. By tracing the replenishment
process on a run chart it was possible to highlight process fluctuations
and then identify the underlying causes of their problem. By: Mike Sondalini, Enterprise Asset Management Columnist for Cheresources.com |
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