Quality Progress - August 2015 - 50

STATISTICS ROUNDTABLE BY LYNNE B. HARE Are the Data the Data? What you see in production line data isn't always what you get AN ARGUMENT BROKE out over a data? And what might be the real message where samples had been removed from large set of production data. Can you in the data? the stream of cookie dough. The blank spots were all on the close side of the imagine such a thing? At issue were some large financial implications. Who you gon- Are all data created equal? stream. The bakers and I had missed this na call? A statistician, of course-namely, For starters, we might wonder how the important aspect of sampling. Some quick me. The team consisted of subject matter data were created. Are all the potential inspection showed cookie dough weights experts, production experts and manage- sources of variation represented in the to be 10% higher on the unsampled side ment. data? If not, all bets are off. of the dough stream, and the sampling Subject matter and production experts Often, statisticians will recommend problem was quickly resolved. talked about the large mass of production random sampling or systematic sampling. line data accumulated over the years. Of If sampling is truly random, every unit Data disruptions course, they didn't have time to clean up produced has an equal chance of appear- Next, we would want to know what the data before making it available to the ing in the sample. Systematic sampling is happens to the data between the time rest of us, they said. usually more convenient in manufactur- an observation is made and when it is ing. There, sampling frequency is tied recorded. That sounds like precious little to the clock; every 30 or 60 minutes, for room for error. What could possibly go instance, with representative samples wrong? Sometimes the errors are subtle, taken at those times. but no less present. That's as it should be, the bosses said. The data are the data. That comment got me wondering. Are the data really the data? Perhaps from the management perspective, they I recall that once, in a short course on Fat fingers: One kind of error ap- constitute the actual record. Therefore, process variation reduction for cookie pears in data entry, especially, but not they are the data. But my questions were: bakers in Spain, we discussed the need exclusively, during manual data entry. Do they represent what really went on in to accumulate representative samples Sometimes referred to as the "fat finger the manufacturing process? Do they accu- during each sampling to be sure that all problem," the wrong keys get pressed rately characterize what eventually ended sources of variation were included in the and extreme values are entered into the up in the possession of the consumer? sample. The bakers assured me that they permanent record. If so, the bosses are right. If not, what might be reasons why the data aren't the followed that sampling principle. Later, during a factory tour, I saw In the case of extremes, data elimination may be beneficial. For example, a value of 812 is obviously wrong, given that Histogram-flinching at a specification / FIGURE 1 production values are centered near 7.9 with a standard deviation of 0.13. Right? Maybe it was meant to be 8.12 or 8.20 or some other number, but we'll never know. It is probably best to discard it. If these extremes are left in the data set, are the data still the data? Flinching: Another kind of error occurs as a result of "flinching." It is very human to edit the data mentally as we enter them. The tendency may be to discard a value and take another sample if we see 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 9 an eyebrow-raising number. After all, one 50 QP * www.qualityprogress.com sample is as good as another, right? http://www.qualityprogress.com

Table of Contents for the Digital Edition of Quality Progress - August 2015

Up Front
LogOn
Expert Answers
Keeping Current
Mr. Pareto Head
Under Construction
Creative by Design
Coming Together
All the Right Moves
3.4 per Million
Quality in the First Person
Career Corner
Statistics Roundtable
Standards Outlook
QP Toolbox
QP Reviews
One Good Idea
Back to Basics

Quality Progress - August 2015

http://www.nxtbook.com/naylor/ASQM/ASQM0719
http://www.nxtbook.com/naylor/ASQM/ASQM0619
http://www.nxtbook.com/naylor/ASQM/ASQM0519
http://www.nxtbook.com/naylor/ASQM/ASQM0419
http://www.nxtbook.com/naylor/ASQM/ASQM0319
http://www.nxtbook.com/naylor/ASQM/ASQM0219
http://www.nxtbook.com/naylor/ASQM/ASQM0119
http://www.nxtbook.com/naylor/ASQM/ASQM1218
http://www.nxtbook.com/naylor/ASQM/ASQM1118
http://www.nxtbook.com/naylor/ASQM/ASQM1018
http://www.nxtbook.com/naylor/ASQM/ASQM0918
http://www.nxtbook.com/naylor/ASQM/ASQM0818
http://www.nxtbook.com/naylor/ASQM/ASQM0718
http://www.nxtbook.com/naylor/ASQM/ASQM0618
http://www.nxtbook.com/naylor/ASQM/ASQM0518
http://www.nxtbook.com/naylor/ASQM/ASQM0418
http://www.nxtbook.com/naylor/ASQM/ASQM0318
http://www.nxtbook.com/naylor/ASQM/ASQM0218
http://www.nxtbook.com/naylor/ASQM/ASQM0118
http://www.nxtbook.com/naylor/ASQM/ASQM1217
http://www.nxtbook.com/naylor/ASQM/ASQM1117
http://www.nxtbook.com/naylor/ASQM/ASQM1017
http://www.nxtbook.com/naylor/ASQM/ASQM0917
http://www.nxtbook.com/naylor/ASQM/ASQM0817
http://www.nxtbook.com/naylor/ASQM/ASQM0717
http://www.nxtbook.com/naylor/ASQM/ASQM0617
http://www.nxtbook.com/naylor/ASQM/ASQM0517
http://www.nxtbook.com/naylor/ASQM/ASQM0417
http://www.nxtbook.com/naylor/ASQM/ASQC12518
http://www.nxtbook.com/naylor/ASQM/ASQM0317
http://www.nxtbook.com/naylor/ASQM/ASQM0217
http://www.nxtbook.com/naylor/ASQM/ASQM0117
http://www.nxtbook.com/naylor/ASQM/ASQM1216
http://www.nxtbook.com/naylor/ASQM/ASQM1116
http://www.nxtbook.com/naylor/ASQM/ASQM1016
http://www.nxtbook.com/naylor/ASQM/ASAC0016
http://www.nxtbook.com/naylor/ASQM/ASQM0916
http://www.nxtbook.com/naylor/ASQM/ASQA0016
http://www.nxtbook.com/naylor/ASQM/ASQM0816
http://www.nxtbook.com/naylor/ASQM/ASQM0716
http://www.nxtbook.com/naylor/ASQM/ASQM0616
http://www.nxtbook.com/naylor/ASQM/ASQM0516
http://www.nxtbook.com/naylor/ASQM/ASQM0416
http://www.nxtbook.com/naylor/ASQM/ASQM0316
http://www.nxtbook.com/naylor/ASQM/ASQM0216
http://www.nxtbook.com/naylor/ASQM/ASQM0116
http://www.nxtbook.com/naylor/ASQM/ASQM1215
http://www.nxtbook.com/naylor/ASQM/ASQM1115
http://www.nxtbook.com/naylor/ASQM/ASQM1015
http://www.nxtbook.com/naylor/ASQM/ASQM0915
http://www.nxtbook.com/naylor/ASQM/ASQM0815
http://www.nxtbook.com/naylor/ASQM/ASQM0715
http://www.nxtbook.com/naylor/ASQM/ASQM0615
http://www.nxtbook.com/naylor/ASQM/ASQM0515
http://www.nxtbook.com/naylor/ASQM/ASQM0315
http://www.nxtbook.com/naylor/ASQM/ASQM0215
http://www.nxtbook.com/naylor/ASQM/ASQM0115
http://www.nxtbook.com/naylor/ASQM/ASQM1214
http://www.nxtbook.com/naylor/ASQM/ASQM1114
http://www.nxtbook.com/naylor/ASQM/ASQM1014
http://www.nxtbook.com/naylor/ASQM/ASQM0914
http://www.nxtbook.com/naylor/ASQM/ASQM0814
http://www.nxtbook.com/naylor/ASQM/ASQM0714
http://www.nxtbook.com/naylor/ASQM/ASQM0614
http://www.nxtbook.com/naylor/ASQM/ASQM0514
http://www.nxtbook.com/naylor/ASQM/ASQM0414
http://www.nxtbook.com/naylor/ASQM/ASQM0314
http://www.nxtbook.com/naylor/ASQM/ASQM0214
http://www.nxtbook.com/naylor/ASQM/ASQM0114
http://www.nxtbook.com/naylor/ASQM/ASQM1213
http://www.nxtbook.com/naylor/ASQM/ASQM1113
http://www.nxtbook.com/naylor/ASQM/ASQM1013
http://www.nxtbook.com/naylor/ASQM/ASQM0913
http://www.nxtbook.com/naylor/ASQM/ASQM0813
http://www.nxtbook.com/naylor/ASQM/ASQM0713
http://www.nxtbook.com/naylor/ASQM/ASQM0613
http://www.nxtbook.com/naylor/ASQM/ASQM0513
http://www.nxtbook.com/naylor/ASQM/ASQM0413
http://www.nxtbook.com/naylor/ASQM/ASQM0313
http://www.nxtbook.com/nxtbooks/naylor/ASQM0213
http://www.nxtbook.com/nxtbooks/naylor/ASQM0113
http://www.nxtbook.com/nxtbooks/naylor/ASQM1212
http://www.nxtbook.com/nxtbooks/naylor/ASQM1112
http://www.nxtbook.com/nxtbooks/naylor/ASQM1012
http://www.nxtbook.com/nxtbooks/naylor/ASQM0912
http://www.nxtbookMEDIA.com