statistics

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Jun 12 2022

Perspectives On Probability In Operations

The spirited discussions on LinkedIn about whether probabilities are relative frequencies or quantifications of beliefs are guaranteed to baffle practitioners. They come up in threads about manufacturing quality, supply-chain management, and public health, and do not generate much light. Their participants trade barbs without much civility, and without actually exchanging on substance.

The latest one, by Alexander von Felbert, is among the more thoughtful, and therefore unlikely to inspire rants. I do, however, fault it with using words like “aleatory” or “epistemic” that I don’t think are helpful. I am trying to discuss it here in everyday language, and to apply the concepts to numerically specific cases, with an eye to operations.

While there are genuinely great and not-so-great ideas, the root of the most violent disagreements is elsewhere, with individuals generalizing from different experience bases. You may map probability to reality differently depending on whether you are developing drugs in the pharmaceutical industry, enhancing yield in a semiconductor process, or driving down dppms in auto parts. The math doesn’t care as long as you follow its rules, and it doesn’t invalidate other interpretations.

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By • Data science • 0 • Tags: , , ,

May 14 2015

Where Have The Scatterplots Gone?

What passes for “business analytics” (BI), as advertised by software vendors, is limited to basic and poorly designed charts that fail to show interactions between variables, even though the use of scatterplots and elementary regression is taught to American middle schoolers and to shop floor operators participating in quality circles.

But the software suppliers seem to think that it is beyond the cognitive ability of executives. Technically, scatterplots are not difficult to generate, and there are even techniques to visualize more complex interactions than between pairs of variables, like trendalyzers or 3D scatterplots. And, of course, visualization is only the first step. You usually need other techniques to base any decision on data.

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By • Data science • 4 • Tags: , , ,

Jul 30 2014

“Studies show…” or do they?

Various organization put out studies that, for example, purport to “identify performances and practices in place among U.S. manufacturers.”  The reports contain tables and charts, with narratives about “significant gaps” — without stating any level of significance — or “exponential growth” — as if there were no other kind. They borrow the vocabulary of statistics or data science, but don’t actually use the science; they just use the words to support sweeping statements about what manufacturers should do for the future.

At the bottom of the reports, there usually is a paragraph about the study methodology, explaining that the data was collected as answers to questionnaires mailed to manufacturers and made available on line, with the incentive for recipients to participate  being a free copy of the report. The participants are asked, for example, to rate “the importance of process improvement to their organization’s success over the next five years” on a scale of 1 to 5.

The results are a compilation of subjective answers from a self-selected sample. In marketing, this kind of surveys makes sense. You throw out a questionnaire about a product or a service. The sheer proportion of respondents gives you information about the level of interest in what you are offering, and the responses may further tell you about popular features and shortcomings.

But it is not an effective approach to gauge the state of an industry. For this purpose, you need objective data, either on all companies involved or on a representative sample that you select. Government bodies like the Census Bureau or the Bureau of Labor Statistics collect useful global statistics like value-added per employee or the ratio indirect to direct labor by industry, but they are just a starting point.

Going beyond is so difficult that I don’t know of any successful case. Any serious assessment of a company or factory requires visiting it, interviewing its leaders in person, and reviewing its data. It takes time, money, know-how, and a willing target. It means that the sample has to be small, but there is a clash between the objective of having a representative sample and the constraint of having a sample of the willing.

For these reasons, benchmarking is a more realistic approach, and I know of at least two successful benchmarking studies in manufacturing, both of which, I believe, were funded by the Sloan Foundation:

  • The first was the International Assembly Plant Study, conducted in the late 1980s about the car industry, whose findings were summarized in The Machine That Changed The World in 1990. The goal was not to identify the distribution of manufacturing practices worldwide but to compare the approaches followed in specific plants of specific companies, for the purpose of learning. Among other things, the use of the term “Lean” came out of this study.
  • The second is the Competitive Semiconductor Manufacturing Program, which started in the early 1990s with a benchmarking study of wafer fabrication facilities worldwide. It did not have the public impact of the car assembly plant study, but it did provide valuable information to industry participants.

The car study was conducted out of MIT; the semiconductor study, out of UC Berkeley. Leadership from prestigious academic organizations helped in convincing companies to participate and provided students to collect and analyze the data. Consulting firms might have had better expertise, but could not have been perceived as neutral with respect to the approaches used by the different participants.

The bottom line is that studies based on subjective answers from a self-selected sample are not worth the disk space you can download them onto.

By • Management • 4 • Tags: , , , , ,

May 13 2014

The GM Toyota Rating Scale | Bill Waddell

See on Scoop.it – lean manufacturing

“In a survey of suppliers on their working relationships with the six major U.S. auto makers – Toyota, Honda, Nissan, Ford, Chrysler and GM – GM scored the worst.  But of course they did.  They are GM and we can always count on such results from them. […] Toyota scored highest with a ranking of 318, followed by Honda at 295, Nissan at 273, Ford at 267, Chrysler at 245, with GM trotting along behind the rest with an embarrassing 244.”

 

Michel Baudin‘s comments:

While I am not overly surprised at the outcome, I am concerned about the analysis method. The scores are weighted counts of subjective assessments, with people being asked to rate, for example, the “Supplier-Company overall working relationship” or “Suppliers’ opportunity to make acceptable returns over the long term.”

This is not exactly like the length of a rod after cutting or the sales of Model X last month. There is no objective yardstick, and two individuals might rate the same company behavior differently.

It is not overly difficult to think of more objective metrics, such as, for example, the “divorce rate” within a supplier network. What is the rate at which existing suppliers disappear from the network and others come in? The friction within a given Supplier-Customer relationship could be assessed from the number of incidents like the customer paying late or the supplier missing deliveries…

Such data is more challenging to collect, but supports more solid inferences than opinions.

See on www.idatix.com

By • Blog clippings • 1 • Tags: , , , ,

Jul 9 2013

Betting on Lean, or …. Analytics versus Empowerment | Bill Waddell

See on Scoop.it – lean manufacturing

“Management is all about playing the odds. […]  In operations, calculate lot sizes, generate forecasts and set quality standards with enough data and increasingly sophisticated algorithms and statistical methods and you will increase the chances of coming close enough.  At least that is the theory, and the hope.

This is the basic premise of big data and ERP.  With point of sale scanning, RFID, smart phones and all of the other data collecting technologies increasingly in use, the data to feed the engines is more and more available.  The potential and the lure of the data driven, analytical approach to finding the center line and getting more decisions closer to correctness is growing.

The other approach is empowered people.  Recognizing that management cannot be involved in every one of the individual customer interactions and operational, situational, tiny decisions, those calls are left to the people on the spot.  They are expected to rely on their knowledge, understanding of company values and goals, and the information available to them in very real time to decide what to do.[…] The basic question is whether empowered people will get it right more often than big computer.”

Michel Baudin‘s insight:

In this article, Bill Waddell presents the data-driven approach to management decision making as contradictory to people empowerment. I do not see these as mutually exclusive.

In 1993, there was a group within Toyota’s logistics organization in the US that, based on weather data, thought that the Mississippi might flood the railroad routes used to ship parts from the Midwest to the NUMMI plant in California. Four days before the flood, they reserved all the trucking available in the Chicago area, for the daily cost of 6 minutes of production at NUMMI. When the flood hit, they were able to ship the parts by truck around the flood zone, and NUMMI didn’t miss a beat.

This is what a good data scientist  does.

In Numbersense, Kaiser Fung points out that data analysis isn’t just about the data, but also about the assumptions people make about it. As an example, he points out the Republican polling fiasco of the 2012 election, as being due to the combination of flawed data collection and equally flawed modeling.

In other words, it’s not a computer that comes up with answers from data, but a human being, and the quality of these answers depends as much on the human analyst’s understanding of the underlying reality as it does on the ability to collect clicks from the web or transactions from point-of-sale systems.

Good data analysis does not require petabytes of data. In statistics, a small sample is 10 points; a large sample, 100 points. The difference matters because, with small samples, there are many convenient approximations that you cannot make. But 100 points is plenty for these approximations to work.

With millions of points, the tiniest wiggle in your data will show overwhelming significance in any statistical test, which means that these test are not much use in that context. To figure out what this tiny wiggle is telling you about reality, however, you still need to understand the world the data is coming from.

I don’t see an opposition between relying on people and relying on data, because, whether you realize it or not, you are never relying on data, only on people’s ability to make sense of it.

See on www.idatix.com

By • Blog clippings • 0 • Tags: , , , , ,