By the numbers: How to study a process

Analyze your data according to mean, median, mode and range.

December 4, 2017
by Richard Kunst

Analyze your data according to mean, median, mode and range. Image: Fotolia

Gemba walks encourage leaders to go where the action is and observe processes. It’s a good starting tactic, but not enough.

Taiichi Ohno, father of the Toyota Production System, coached his leaders to carefully observe reality by drawing a chalk circle on the floor, stand in it for several hours and observe reality with their minds wiped clean, undistracted by things seemingly more important to do. This intensive practice imbued them in kaizen thinking, which was necessary before they could coach others.

So go to the gemba and stand in an imaginary circle to really observe a process for at least 30 minutes while taking lots of notes (read more about standing in the circle here).

But sometimes you need to go beyond observation and study the numbers.

Most processes track outputs, so grab production documents from at least the three previous months and plot the numbers on a graph.

Why three months? Because you need a minimum of 30 data points to establish a trend.

The target output was likely envisioned by the engineer who designed the process and it became the standard for costing and usually twice the rate of demonstrated output, which includes all of the noise and disturbances to flow that impact the process. Since it has been demonstrated, this is what the teams should consistently achieve.

Analyze the data

When people analyse data the typical approach is to calculate averages, but they won’t reveal whether or not your process is actually in control.

Instead, analyze data in mean, median, mode and range. If the process is under control, the three Ms should be very close with your range at its minimum.

Mean, median and mode are three kinds of averages. Mean is the average where you add up all the numbers and divide by the number of numerals.

Median is the middle value. The numbers have to be listed in order from smallest to largest.
Mode is the value that occurs most often. If no number in the list is repeated, there is no mode for the list.

The following example will help with the calculations:

To find the mean add and divide these numbers: (13 + 18 + 13 + 14 + 13 + 16 + 14 + 21 + 13) ÷ 9 = 15.

Note that the mean isn’t a value from the original list.

Don’t assume it will be. This is a common result.

To find the median, rewrite the list in numerical order: 13, 13, 13, 13, 14, 14, 16, 18, 21. There are nine numbers in the list, so the middle one (median) is 14.

The mode is the number that’s repeated more often than any other, so it’s 13.

The largest value in the list is 21, and the smallest is 13, so the range is 21 – 13 = 8.

Of course, by the numbers isn’t the only way to go, but it certainly enhances what comes out of the circle.

Richard Kunst is president and CEO of Cambridge, Ont.-based Kunst Solutions Corp. Visit E-mail

This article appeared in the September 2017 issue of PLANT.

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