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Suppose you had 16 months of data on an important process (as plotted on the run chart seen in figure 1). For improvement purposes, an intervention was made after the sixth observation to lower this key process indicator. This intervention is equivalent to creating a special cause for a desired effect.
There is no trend as defined statistically (despite the trend downward of length five from observations 5 to 9; with 16 data points, one would need length six, or five successive decreases). Neither is there any run of length eight either all above or below the median. So, would you want to conclude that the intervention had no effect? I doubt it!
Think of the median as a reference, and consider each data point as a 50-50 coin flip (heads = above the median; tails = below the median). The question is: Would you expect to flip a coin 16 times and obtain the specific pattern of seven heads (run of length seven above the median), immediately followed by seven tails (run of length seven below the median), then a head (run of length one above the median) and, finally, a tail (run of length one below the median)? Intuition would seem to say, “No.” Is there a statistical way to prove it?
Here’s a story that proves once again that exciting quality applications can occur anywhere in the world.
BHP Billiton operates the EKATI diamond mine in Canada’s Northwest Territories, approximately 200 miles northeast of Yellowknife—just below the Arctic Circle. Arctic winter gear is standard attire during the long winters, when the sun barely rises above the horizon. Although the setting is harsh, it can also be a beautiful place to observe and enjoy a truly unique perspective on nature—on those rare days when the temperatures rise above freezing and there aren’t any grizzly bear problems.
The hardy folk who work at the EKATI mine demand equally hardy and adaptable tools to help them do their jobs and ensure quality. Management at the EKATI mine is proud of its reputation as the safest, lowest-cost producer of quality diamonds in the world. BHP Billiton has a long commitment to quality excellence and improvement, not only in maximizing business efficiencies, but also within the areas of health and safety, environmental stewardship, and community relations.
Teledyne Microelectronic Technologies, a Teledyne Technologies Inc. company, is a microelectronics manufacturer specializing in products and services for the defense, space, aviation, medical, and broadband communications markets. Because these markets are highly regulated, Teledyne maintains a quality management system certification to SAE AS9100, ISO 9001, and major OEM customer specifications.
The challenge for Teledyne was to balance quality, compliance, and costs. Environmental monitoring is crucial because of the electrostatic discharge damage that can occur when temperature and relative humidity levels do not meet minimum/maximum criteria. The ambient humidity levels can decrease significantly throughout the year.
Cequent Transportation Accessories, a division of TriMas Corp., located in Bloomfield Hills, Michigan, designs and manufactures a broad range of accessories for light trucks, SUVs, recreational vehicles, passenger cars, and trailers. The company has a long history of using enterprise quality management to drive market success.
Three years ago, Chinese supplier error levels were unacceptable and in direct conflict with the requirements expected of Cequent’s domestic suppliers. In an effort to mitigate this risk and improve quality, Cequent used the global quality infrastructure from IQS, of Cleveland, Ohio, to implement a successful domestic quality and compliance program.
As the world seeks to extricate itself from the worst financial crisis for many decades, many senior risk professionals and independent experts are asking about the roles, responsibilities, and limitations of risk management in the world’s financial institutions. Are the tools available to risk managers fit for the purpose? Is there appropriate expertise and leadership at a senior level to guide risk management? Do risk managers lack authority to rein in the excesses of risk-takers? Is there sufficient understanding of potential risk concentrations across institutions’ full range of operations?
I always look forward to this time of year. Not in anticipation of prezzies under the tree, but for what changes 2009 will bring.
First, this issue brings you the last columns for two long-time columnists.
Davis Balestracci’s no-nonsense approach to statistics has been popular with our readers for four years. Irreverent, confrontational, and, hey, let’s say it, just a bit feisty, Davis has challenged our readers’ inbred assumptions about when and how to use statistics. Thanks, Davis, for four years of wit and wisdom and showing us how to “plot the dots.”
Stepping in to take Davis’ place is a man often quoted by Davis, Donald J. Wheeler. As the author of 24 books and hundreds of articles, he is one of the leading authorities on statistical process control and applied data analysis. He is a Fellow of both the American Statistical Association and the American Society for Quality. Don was also Quality Digest’s SPC columnist from January 1996 to December 1997. Welcome back, Don.
The International Manufacturing Technology Show 2008, held in Chicago, Illinois, September 8-13, posted its largest attendance since the year 2000. Total registration for the six-day event was 92,450, with 1,803 exhibiting companies.
“We are ecstatic that IMTS 2008 not only achieved but exceeded expectations and objectives,” states Peter Eelman, IMTS vice president of exhibitions. “The feedback from exhibitors and the purchasing activities of attendees prove that manufacturing is not only healthy, but thriving. Manufacturers coming to the show from around the world clearly understand that investing in the latest technology is key to being competitive.”
Purchasing activity was high, along with healthy traffic on the show floor. Some highlights for attendees and exhibitors included the introduction of software standard MTConnect, the Advanced Manufacturing Center, the new Innovation Center, and the National Institute of Metalworking Skills (NIMS) Student Summit, and a press conference from Hexagon Metrology.
The hydraulic casting components made at Rexroth Guss, a subsidiary of Bosch Rexroth, are characterized by their complex, core-intensive construction and many free-form surfaces. These costly parts, made of cast iron or spheroidal graphite iron, are invariably designed in 3-D CAD software. The transition from 2-D to 3-D design prompted the quality department to look for an appropriate measuring solution to inspect their parts.
“ The requirements for quality assurance have increased with 3-D technologies,” says Frank Mill, quality manager at Rexroth Guss. “Earlier, all major dimensions could be taken from a 2-D drawing for tactile measurement, which is no longer the case. Modern 3-D drawings include little in the way of explicit dimensions. The curves of the free-form surfaces are almost impossible to verify using traditional tactile measurement techniques.”
Take a look at the control chart in figure 1. There are no observations outside the common-cause limits, but there are five special-cause flags:
• Observation 5: Two out of three consecutive points greater than two standard deviations away from the mean
• Observations 21 and 30-32: Four out of five consecutive points greater than one standard deviation away from the mean
So, what do you do? Treat them as five individual special causes? Say, “Well, if you look at it realistically, there really seems to be three ‘clumps’ of special cause?” Because the last seven observations all fall below the mean, some readers might want to call them special causes as well. Maybe nothing should be done because no individual points are outside of the limits.
What have been your experiences?
As I’ve tried to emphasize time and again in this column, always do a run chart of your data first (as seen in figure 2).
Ten Steps to Address Risk Management 
