Elsmar Cove Forums Index - Liars Figure and Figures Lie

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Liars Figure and Figures Lie
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Posted by: Steve Prevette

I published this a few years back in our local ASQ newsletter. Actually I have since found out the "Lies ****ed Lies and Statistics" quote is attributable to Disraeli, not Mark Twain (though he used it with attribution to its source).

late entry

Interesting - I see the editor edited me automatically. So I will continue the story - I did write (and officially cleared by the US Government) a paper called Lies ****ed Lies and Statistics" this year. They held an authors breakfast, and since I made the database of the authors and papers, I made sure the MC read off that title. . .

Posted by: Charmed

Dear Steve: Excellent article. You have highlighted three problems very nicely. Now, I have a question about the fourth. If we take any 25 numbers, such as what you have, can we necessarily say that they follow the "normal" distribution. Quite coincidentally, I was looking at an exactly similar problem and I came to the conclusion that the numbers do not represent a normal distribution. I did not "randomize" them using a random number generator, but did do some other types of "randomizing." Again, thanks for a lovely and thought provoking article.

Charmed

Posted by: Greg B

Steve,

Great little article. It is very easy to understand and gets across a very big picture of the problems with charting and the way data is projected.

I must admit that I have abused graphs to get a point across or to win an argument. My problem has always been that people usually see the negative of the graph, as your 'LIE' graphs have shown, and resort to the blame game, as stated.

It is sooo easy to increase or decrease the data (add a Good month/period or drop off a bad month/period etc) to suit the point you wish to make. I find this especially true when charting 'Lag' Indicators such as LTIs or Corrective Actions. If I want to push a point, good ro bad, I can paint a suitable picture by showing a graph with 'Selected' data that shows a marked increase/decrease over a given period. It has come in handy from time to time. The worrying thing is that no-one has picked it up....ever.

We us the 'Control Chart' for tracking our Product Specification Results with a UCL and LCL set. We then only report on those that breach these limits.

Greg B

Posted by: Steve Prevette

Quote:

Originally Posted by Charmed

Dear Steve: Excellent article. You have highlighted three problems very nicely. Now, I have a question about the fourth. If we take any 25 numbers, such as what you have, can we necessarily say that they follow the "normal" distribution. Quite coincidentally, I was looking at an exactly similar problem and I came to the conclusion that the numbers do not represent a normal distribution. I did not "randomize" them using a random number generator, but did do some other types of "randomizing." Again, thanks for a lovely and thought provoking article.

Charmed

You are very correct - they are not normal. I simply used a uniform distribution. Anticipating the next question - Dr. Shewhart tested control charting with not only the normal distribution, but also a uniform distribution, and also a triangular distribution. Control charting is very robust to non-normal distributions, and does not (versus how most people teach SPC) rely on the normal distribution. The true basis, as stated by Dr. Shewhart is the Tchebychev Inequality. Perhaps that discussion would make a good follow on article, though I must admit Dr. Wheeler has done a lot of work already in that area.

OOPS, rewind, rewind. As I looked at the file again, I did shift the uniform data to a normal distribution. If you double click on the charts, you can find the underlying excel file (which is why the file is somewhat large, lately I have been trying to be sure that only the chart object comes into the word file). You can see my random number generator routine.

Posted by: Mike S.

I like it, Steve. Good job. Do we get to read "Lies ****ed Lies and Statistics"?

Posted by: Steve Prevette

Quote:

Originally Posted by Mike S.

I like it, Steve. Good job. Do we get to read "Lies ****ed Lies and Statistics"?

I gotta pace myself - can't give away all my secrets at once

Posted by: J Oliphant

Steve, whether you win $150 or not. I LOVE your articles!!

I think the best part of this article is the very end. where after several conflicting interpretations of the data - you reveal that the data has no information at all.

This is one of your best.

Posted by: Charmed

Dear Steve:

I just finished reading your May 2004 article, "Tyrrany of Targets" - An argument against Management by Objective. Another lovely article. I notice that you have used the same control chart example in both articles. Do you have the actual values that were used to prepare the control chart? If it is not a bother, can you post the numbers?

***********

Never mind Steve, I read your response to another question and was able to get the number by double clicking on the Figures. I rounded off each value to two-decimal places and calculated the average and the standard deviations. I was also able to get the same least squares regression equation that you got, in spite of the rounding-off two decimal places.

Charmed

Posted by: ccochran

Steve,

Very nice, concise article. It uses an economy of words to explain a confusing issue. You know, a simply eye-ball analysis of the data in the bar chart reveals that we were dealing with random variation in the first place, but people love to interpret all kinds of meaning into data that doesn't exist. The control chart confirms our suspicion that the data represents nothing more than the random variation of a stable system. Keep up your fine writing.

Craig

Posted by: Steve Prevette

Quote:

Originally Posted by ccochran

Steve,

Very nice, concise article. It uses an economy of words to explain a confusing issue. You know, a simply eye-ball analysis of the data in the bar chart reveals that we were dealing with random variation in the first place, but people love to interpret all kinds of meaning into data that doesn't exist. The control chart confirms our suspicion that the data represents nothing more than the random variation of a stable system. Keep up your fine writing.

Craig

Somehow, people have lost the ability to "eyeball" data. In that regard, we may have been better off before computers and ways to beat data into submission and before Power Point.

Posted by: Craig H.

Quote:

Originally Posted by Steve Prevette

Somehow, people have lost the ability to "eyeball" data. In that regard, we may have been better off before computers and ways to beat data into submission and before Power Point.

Steve:

First, a great article. If I may, I would like to keep it handy to use as ammunition.....

I agree about "eyeballing" data, and will go one further. Often I have seen people take a data set at face value, and not really look at where the data came from, and how it was gathered, one of the things my STAT 101 Professor repeated often.

Anyhow, enjoyed reading your work!

Craig H.

Posted by: Steve Prevette

Quote:

Originally Posted by Craig H.

If I may, I would like to keep it handy to use as ammunition.....

Craig H.

Please do use it. That is what it is here for, of course please attribute myself and the Cove as the source.

Posted by: sal881vw

A very goog article, Steve. I always believed that control charts give a true indication.

Posted by: S Roche Hendrix

Thanks for this article. I will also use to help others understand the importance of correctly interpreting data. I am on a mission to get more of our management to "think statistically". Oh the countless hours many have spent (wasted) trying to determine what has changed when there is no change! I will add in my explanation, though, that "stable" and "no significant trends" does not necessarily mean all is well. If the difference between Nov-99 and Jan-00 resulted in significant losses, let's face it, management does not really care. What this does do for us, is direct our investigation from "special causes" to "normal causes". We must then convince management that the process must be changed to either move the average or reduce the variation. Having worked for a management team that understands this is priceless!

Thanks again.

Posted by: Claes Gefvenberg

Great summary Steve,

You keep coming up with interesting subjects. I have of course seen and reacted to all the three big lies you mention, as well as to some variations of them. Some even more "novel" methods of presenting data has been duly noted over the years.

Your examples are all easy to read. I suppose that we have all seen graphs that are anything but easy to interpret, and that must sometimes be regarded as yet another way to deliberately muddy the waters. My pet peeve in that respect must be when trends are exaggerated by cutting an axis in a line diagram.

/Claes

Posted by: M Greenaway

Great subject, another which I often try to convey to looks of bewilderment.