# Quality Digest

By Davis Balestracci

#### Don’t let the calculation scare you; it looks worse than it is.

Given the data in my June column, “Percentage Deceptiveness,” suppose I wanted to compare the performance of months 1-33 (survival rate of 98.6%) vs. months 34-51 (survival rate of 98.1%). I could use a p-chart analysis of means (ANOM), but because of only one decision being made, the three standard deviation limits would be very conservative. Not only that, the problem of unequal denominators negates using ANOM’s more exact limits (1.39 standard deviations) for comparing two percentages at a 5-percent significance level. In cases like this, there is a nice alternative usually available in most good statistical software packages.

You can create what is called a “2 × 2 table” as shown in figure 1.

Figure 2 shows the generic structure of such data so that you can understand the needed statistical calculation.

By Quality Digest

Regarding “Big Boxes Beware” (“First Word,” Dirk Dusharme, November 2008): If you want to experience grocery-industry customer service at its finest, visit Wegmans. Their employees will load your groceries in your car for free, provide umbrellas for trips to your car in the rain for those who don’t have one, and personally take you to the items that you’re looking for when you can’t find something.

Those needing a lesson in customer service should shop there a time or two. They will learn what service is all about.

--Chris Wallen

Hear! Hear! My boss was commenting today that he went to “Wally World” on his way to work and tried to buy light bulbs. First of all, he was looking for 100-watt bulbs and the closest that they sell now are the 90-watt kind.

When he went to check out, the register sign was lit up, but no one was there to run the register. He stepped back far enough to see two workers stocking an end cap. They looked his way three times and still went back to stocking.

On the third time, my boss said he even waved at them so that they would see movement at the register. Needless to say, when he left, the light bulbs were still on the counter.

--Mike Janes

By Donald J. Wheeler

Many have been taught that they must remove outliers prior to analysis. This is because much of modern statistics is concerned with creating a mathematical model for the data. Because all these models are created using algorithms, they tend to be severely affected by any unusual or extreme values.

Therefore, to use these mathematical techniques to obtain useful and appropriate models, it’s often necessary to polish up the data by removing the outliers. However, the act of building a model implicitly assumes that the data are homogeneous enough to justify the use of a model.

For example, the histogram in figure 1 has a bell-shaped curve superimposed. This curve is based on the average and standard deviation statistic for all 100 values in the histogram. It’s neither wide enough nor tall enough to provide a good fit to the data. The histogram in figure 2 contains the 93 values left after the seven extreme values (the four lowest and three highest) were deleted. Now the curve based on the average and the standard deviation statistic does a much better job of fitting the data. Thus, it’s true that outliers can undermine our efforts to create a model for our data.

By Nicolette Dalpino

By Quality Digest

### Short on News

Federal Reserve Chairman Ben Bernanke said that financial institutions must address the “fundamental sources of financial strains” in Wall Street’s credit crisis by deleveraging, raising new capital, and improving risk management.
www.thestreet.com/markets/bonds-economy/10416480.html

The naval Surface Warfare Center is leveraging Actuate Corp.’s Performancesoft suite to underpin its Malcolm Baldrige and lean Six Sigma performance management efforts.
www.earthtimes.org/articles/show/
naval-surface-warfare-center-lever ages,
389822.shtml

By Nicolette Dalpino

### 2008 Global Productivity Report

According to the “2008 Global Productivity Report,” the recent annual report from Proudfoot Consulting, staff shortages and internal communications problems are the main barriers to productivity around the globe, with staff shortages cited as the main barrier in the United States. Although companies in emerging markets such as Brazil, Russia, India, and China are most likely to have seen recent gains in productivity, North American executives are the least optimistic about their chances of increasing efficiency, stating that more than 40 percent of potential improvements will remain untapped.

By Dirk Dusharme @ Quality Digest

This issue is the first of three consecutive CMSC show-focus issues that highlight the yearly Coordinate Metrology Systems Conference. The CMSC is the largest U.S. trade show focused solely on large-scale 3-D metrology. Attendance has grown each year, with last year reaching nearly 600 attendees. All the key players in large-scale 3-D measurement are there representing every large-scale 3-D measurement technology, including laser scanners, structured-light scanners, laser radar, photogrammetry, theodolites, articulated arms, indoor GPS, and more.

Our CMSC cover story this month focuses on the use of articulated arms (portable coordinate measurement machines) to align collimators at CERN’s Large Hadron Collider in Switzerland. Steering two high-energy beams traveling in opposite directions around a 27 km-circumference accelerator so that they collide head on at a predetermined point requires the most accurate in 3-D metrology equipment. You can read how they did it starting on page 22.

Quality Digest is proud to have been the sole media sponsor for the CMSC show for four years, and we look forward to continuing our coverage of the ever-evolving field of large-scale 3-D metrology.

By Dirk Dusharme @ Quality Digest

It’s almost like some retailers finally read the memo. They seem to now understand that customer service is the new differentiator. With quality levels and prices across almost all product categories nearly at par, it’s service that sets retailers apart--and smaller retailers have taken note.

I was recently at a new Safeway supermarket looking for dried currants. I asked the nearest floor person where I could find them, expecting a simple “look at the end of aisle 10.” Instead, the clerk told me she wasn’t sure but she could find someone who would know. She came back with a young guy in tow who walked me to the produce department and helped me find the product. This has happened numerous times recently at Safeway, Raley’s/Bel Air, Trader Joe’s, and a few other national and regional retailers. In fact, this rush to help almost seems to have happened overnight.

Sometimes the service has been almost embarrassing. I almost felt bad when a Raley’s employee spent 15 minutes helping me find tahini. I mean, neither of us even knew what it was, but there we were, marching up and down the aisles just so I could satisfy my wife’s craving for homemade hummus.

By Davis Balestracci

Eighty-four doctors treated 2,973 patients, and an undesirable incident occurred in 13 of the treatments (11 doctors with one incident and one doctor with two incidents), a rate of 0.437 percent. A p-chart analysis of means (ANOM) for these data is shown in figure 1.

This analysis is dubious. A good rule of thumb: Multiplying the overall average rate by the number of cases for an individual should yield the possibility of at least five cases. Each doctor would need 1,000 cases to even begin to come close to this!

The table in figure 2 uses the technique discussed in last month’s column, “A Handy Technique to Have in Your Back Pocket,” calculating both “uncorrected” and “corrected” chi-square. Similar to the philosophy of ANOM, I take each doctor’s performance out of the aggregate and compare it to those remaining to see whether they are statistically different. For example, in figure 2, during the first doctor’s performance, one patient in the 199 patient treatments had the incident occur. So, I compared his rate of 1/199 to the remaining 12/2,774.

By by Nicolette Dalpino and Carey Wilson

### Short on News

NIST has developed the first detailed chemical analysis revealing what processing is needed to transform crude oil made from pig manure into fuel for vehicles and heating.
www.nist.gov/public_affairs/
techbeat/
tb2008_0610.htm#crude

The average refrigerator sold today consumes less energy than a 60-watt light bulb left on 24 hours a day.
www.aham.org/ht/a/
GetDocumentAction/i/34442