Jan 24 2022
Does Amazon Use Lean, Six Sigma, or Lean Six Sigma?
In 2019, Christoph Roser posted six articles on his blog about the inner workings of Amazon Fulfillment Centers, based on visits to locations in the US and Germany. His blog is called AllAboutLean but the word “Lean” appears nowhere in his articles about Amazon. “Six Sigma” does not appear either, and Christoph does not mention meeting any black belt.
In addition, in Working Backwards: Insights, Stories, and Secrets from Inside Amazon (2021), Amazon alumni Colin Bryar and Bill Carr make no reference to Lean, and all they report about Six Sigma is using DMAIC to define metrics.
Yet you find some published descriptions of Amazon as a showcase for Lean, Six Sigma, or Lean Six Sigma but, if you consider them without confirmation bias, the evidence is underwhelming. The keywords appear, along with a few more, like “Operational Excellence” or “Scrum.”
Based on the small amount of published data, the leaders of Amazon, starting with Jeff Bezos, “learned a bunch of techniques, like Six Sigma and lean manufacturing and other incredibly useful approaches.”
In other words, they learned everything they could get their hands on while staking out uncharted territory. Then they developed their own system. Now they are sharing with outsiders a few homilies but no details, as is their privilege. Their system is to retail as Toyota’s is to manufacturing. It’s not reducible to Lean, Six Sigma, or Lean Six Sigma.
Oct 4 2022
Strange Statements About Probability Models | Don Wheeler | Quality Digest
In his latest column in Quality Digest, Don Wheeler wrote the following blanket statements, free of any caveat:
Source: Wheeler, D. (2022) Converting Capabilities, What difference does the probability model make? Quality Digest
Michel Baudin‘s comments:
Not all models assume i.i.d. variables
Wheeler’s first statement might have applied 100 years ago. Today, however, there are many models in probability that are not based on the assumption that data are “observations from a set of random variables that are independent and identically distributed”:
Probability Models Are Useful
In his second statement, Wheeler seems determined to deter engineers and managers from studying probability. If a prominent statistician tells them it serves no useful purpose, why bother? It is particularly odd when you consider that Wheeler’s beloved XmR/Process Behavior charts use control limits based on the model of observations as the sum of a constant and a Gaussian white noise.
Probability models have many useful purposes. They can keep from pursuing special causes for mere fluctuations and help you find root causes of actual problems. They also help you plan your supply chain and dimension your production lines.
Histograms are Old-Hat; Use KDE Instead
As Wheeler also says, “Many people have been taught that the first step in the statistical inquisition of their data is to fit some probability model to the histogram.” It’s time to learn something new, that takes advantage of IT developments since Karl Pearson invented the histogram in 1891.
Fitting models to a sample of 250 points based on a histogram is old-hat. A small dataset today is more 30,000 points, and you visualize its distribution with kernel density estimation(KDE), not histograms.
#donwheeler, #probability, #quality
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By Michel Baudin • Press clippings 8 • Tags: Don Wheeler, Probability, Quality