Statistics Posts for Improvement Insights

Improvement Insights Blog

Latest "Statistics" Posts

Jay is the Fourth Horse of Statistics

Everyone thinks I’m a statistician by trade, but nothing could be further from the truth. Here’s my journey.

“Hi, this is Jay Arthur, author of “Lean Six Sigma Demystified” and the QI Macros [software]. I’m here in Maui Kaanapali Villas in Maui.

“One of the things that I want you to think about is because I wrote the QI Macros, everybody thinks I’m a statistician or something, but… the truth is a little bit further from that.

“Suzuki the Zen master had a story of four horses: One ran easily, one you had to flog it a little bit, one he had to flog a little more, and the fourth one you had to flog a lot to get it to move.

Posted by Jay Arthur in Improvement Insights, QI Macros, Statistics.

Trendlines Are Rarely Improvements

At the 2018 Magnet Nursing conference in Denver, I saw many improvement posters using line or bar charts with an added trend line to show improvement. Unfortunately, few of the trends were valid. Here’s why:

Posted by Jay Arthur in Improvement Insights, QI Macros, Statistics.

20th vs 21st Century Quality

Too many quality professionals are clinging to the way things have always been done. There’s some sort of taboo about doing things quickly and easily. What are the differences between 20th and 21st Century Quality? Watch and find out:

Posted by Jay Arthur in Data Mining, Improvement Insights, QI Macros, Six Sigma, Statistics.

The Book of Why?

Statisticians say “correlation does not equal causation,” but what if we can prove cause and effect using new tools? The Book of Why, by Judea Pearl explains how this new science of cause and effect has shifted statistics over the last 30 years.

Posted by Jay Arthur in Improvement Insights, Statistics.

Fear of Ridicule and What to Do About It

I’ve noticed a disturbing trend. Customers call us wanting to know all of the background about the hows, whys and formulas of a chart. I think they are afraid someone will challenge or ridicule their analysis. Here’s what I think.

Posted by Jay Arthur in Improvement Insights, QI Macros, Six Sigma, Statistics.

Statistics are Simple

People have been trying to make statistics simple and easy to understand for decades.

But statistics aren’t simple. Maybe we should change how we teach them?

Posted by Jay Arthur in Improvement Insights, QI Macros, Statistics.

Are We Teaching Students the Unnecessary Things?

I’m here at the IISE (Institute of Industrial and Systems Engineers) conference in Pittsburgh.

One professor had been teaching students how to use Excel to create control charts, but he was beginning to feel like that was a waste of classroom time (duh!).

I beat him up a little for teaching DIY Excel stuff to students. If the professor does it, they think that’s how it’s done. With QI Macros he can get them right into analysis.

I feel the same way at ASA (American Statistical Association) when they use “R” to do statistics. Sure it’s free, but should statisticians be programming in “R” or just using software to achieve the same result.

Posted by Jay Arthur in Healthcare, Lean, Manufacturing, Service, Six Sigma, Statistics.

Use XmR Charts instead of c, np, p and u Charts

I have found that an XmR chart is the easiest way to display attribute data. Simply convert the numerator/denominator into a ratio and plot the ratio.

  • defects per day could be a c chart, but an XmR chart works just as well
  • defects/samplesize could be np, p or u chart, but XmR chart works just as well using the ratio

Almost two decades ago, Tom Pyzdek said: X chart provides an excellent approximation to the p chart.

More recently, Donald Wheeler noted that XmR chart limits will be very close to c, np, p or u chart limits if the underlying distribution is correct.

Posted by Jay Arthur in QI Macros, Six Sigma, Statistics.

What USL/LSL Do I Need for Cp>1?

Customer asked me what seemed like a strange question: What specification limits do I need to get a Cp greater than one? Usually her customer should set specification limits, but her boss wanted to know what they could deliver. Hmmmm!

Then I realized that since QI Macros templates (e.g., XmR chart) calculate the average and sigma estimator, the LSL/USL for Cp = 1.0 would be:

LSL = Average – 3*SigEst     USL = Average+ 3*SigEst

For Cp = 1.33, just change the 3 to a 4; Cp = 1.66, change the 3 to a 5. Here’s an XmR chart template with some sample data and calculations to reverse engineer spec limits:



Posted by Jay Arthur in QI Macros, Six Sigma, Statistics.

Statistical Bullies

At IHI, I spoke with one Quality Improvement Adviser who was getting blow back from certain statisticians in her organization. They were challenging her methods and tools and analysis.

As I have written before, I call these folks “Stat Bastards” because they belittle others rather than help them.

As a member of the American Statistical Association, almost every statistician I meet is incredibly kind, generous and helpful. The few that flaunt their training rather than helping are impeding the forward progress of their organization.

I say, if they have better data, bring it. If they have better analysis, bring it. If they have better tools, bring it.

Posted by Jay Arthur in Six Sigma, Statistics.