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Latest "Statistics" Posts

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 […]

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 […]

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 […]

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 […]

Posted by Jay Arthur in Six Sigma, Statistics.

Users Barely Using Excel

Renu Davi, Sr. Program Manager for Excel, reported at Excelapaloosa that two-thirds of the 650 million users use Excel to make lists. The other third of users do deeper analysis, but I’m wondering how? Microsoft keeps tabs on Excel usage. Here’s some statistics for usage in an Excel workbook: Only 4.3% have a function like SUM(A1:B2) 7.5% have […]

Posted by Jay Arthur in QI Macros, Statistics.

Data Visualizations that Really Work

The June, 2016 HRB article by Scott Berinato examines how to use charts and diagrams to express ideas and statistics. I agree with Anmol Garg, Tesla data scientist quoted in the article, “You can’t find anything looking at spreadsheets and querying databases. It has to be visual.” Bernato says: “Convenient is a tempting replacement for […]

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

Cp Cpk Formula Mistakes

A customer sent me their home grown template for calculating Cp and Cpk and wondered why the QI Macros got such radically different values. It was easy to see from their data that they were using standard deviation, not Sigma estimator (Rbar/d2) to calculate Cp and Cpk. Use Stdev to calculate Pp and Ppk, not […]

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

Correlation not Causation

As John Johnson and Mike Gluck point out in their book, EVERYDATA, ice cream consumption and murder rates both go up in the summer, but that does not mean that eating ice cream causes murder. Rising summer temperatures seem to be involved. They also provide a link to Tyler Vigen’s website, Spurious Correlations. Does U.S. […]

Posted by Jay Arthur in Jay Arthur Blog, Six Sigma, Statistics.

What’s Wrong with the New Excel 2016’s Box and Whisker Plot?

Microsoft added a box and whisker plot to Excel 2016, but it’s not everything you might hope for. Here’s an Excel 2016 box and whisker plot: You might notice that the whiskers have a crossbar on the end. It seems to have a spare “x” in the middle of each box and it’s a little hard […]

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