Quality Engineering and Taguchi Methods: A Perspective Robust product design and parameter design-methods to develop prod­ ucts that will perform well regardless of changes in uncontrollable envtron­ mental conditions or that are insensitive to component vanatlon-are key concepts in the work of Or. Taguchi. We should encourage. design ~nd manufacturing engineers to apply these useful ideas. But In deslgnlnQ. exper­ iments and analyzing data - key aspects of the practical Implementation - better and simpler methods are available and should be preferred over Taguchi's less intuitive and more cumbersome approaches.

Smen Bisgaard

uring the last few years we have In conjunction with the broader by our competitors, we have the Dwitnessed a surge in interest in vision of quality management we foundation for a better strategy. In quality improvement. Quality im­ are also seeing a rapid development an effort to become more competi­ provement, or as it used to be of new quality engineering concepts. tive, it is important to use the best called, quality control, is a field with In particular, we are hearing a lot and simplest tools available. a loog history that continues to about Taguchi methods. The history Quality Improvement and Quality grow. New contributions are made of quality control, engineering statis­ Engineering every year. In the 1960s and 70s tics, and quality engineering is little Concern about quality of manu­ there was a slump in the Western known and few people can put factured goods goes back as far as development partly because of mis­ Taguchi methods in perspective. But ancient Egypt.' In more modern understanding of the enormous eco­ without a proper perspective, man­ times, pioneering industrialists such nomic benefits of quality control. agers and engineers might commit as Joshua Wedgwood and Henry During that period, quality control Ford emphasized the importance of was mostly perceived as a set of Perhaps the most important delivering high-quality products at a techniques for sorting and final in­ low price and made that philosophy spection of products. Thus, quality development is that in some the basis for their business success. control was seen as an added ex­ companies, management is The earliest applications of sta­ pense. coming to the fundamental tistical methods for quality control This view is rapidly changing. conceptual understanding that date back to the 1920s and are due Many companies are now develop­ quality does not necessarily to Dr. Walter A. Shewhart and his ing a much more visionary associates working for Bell Labora­ company-wide quality improvement come at a higher cost. tories and Western Electric. Through strategy. Perhaps the most impor­ Shewhart's efforts, Quality Control tant development is that in some themselves and their companies to became an engineering discipline in companies, management is coming long-term strategies and expensive its own right. His two books',' are as to the fundamental conceptual un­ educational programs that later important today as when they were derstanding that quality does not might turn out to be imprudent. Al­ first published. Blanton Godfrey has necessarily come at a higher cost. though the review of Taguchi's written an interesting article on the By using quality improvement con­ methods provided in this article is early history of statistical quality cepts, quality engineering methods, somewhat critical, the purpose is not control at Bell Laboratories. 4 and quality management principles, to be negative and in particular not Shewhart inspired many people it is possible to develop products to criticize Dr. Taguchi personally. both in the United States and and processes of higher quality at The intent is instead to alert engi­ abroad. Perhaps he found in Great lower overall cost. In fact, quality neers and managers to the fact that Britain the most receptive foreign management is an integrating con­ although many of Taguchi's engi­ audience. At the time, quality control cept for cost-effective, rational, co­ neering ideas are very useful, his was seen as a way of fending off operative manufacturing of high­ statistical inventions are inefficient, the depression, then at its worst. quality products and for delivering and also more cumbersome and Despite the fact that most of the high-quality services. less intuitive than need be. We can fundamental ideas of quality control do better. This really is good news. If we can improve on the methods used I>

Fall 1989 13 have been around since World War use of the seven tools for solving all from that country and India in the II, quality improvement today seems kinds of problems, manufacturing as 1940s. They have been applied by to be the most promising avenue for well as service-related, at all organi­ quality professionals in the United American industry to follow in its zational levels of Japanese compa­ States and Great Britain since that current struggle to regain competi­ nies has profoundly increased the time. tive strength. This can be said with quality and reduced the cost of their In the same article, Professor confidence, for it is widely acknowl­ products. It is widely believed that Kusaba supplies an interesting table edged that a major reason for the these tools, despite their simplicity reproduced here as Fig. 1. It is a success of many Japanese compa­ (or perhaps because of it), have sig­ statistical tabuiation of methods nies is the use of the quality im­ nificantly contributed to Japan's suc­ used in case studies presented at provement philosophy they originally cess. the Quality Control Annual Confer­ learned from Shewhart's friend and Lately "Taguchi methods" and ences held each year in Japan. long time associate, Dr. W. Edwards Quality Function Deployment (QFD) From this tabie it is clear that the Deming.s have received attention. Eureka seven toois are in fact the most uti­ writes that "The use of QFD and lized methods and more likely are Always a Better Way of Doing Taguchi Methods has been instru­ key ingredients in Japan's success. Things What is quality improvement? mental in helping Japanese compa­ Note also the use of the generic Without trying to corne up with a nies to improve quality, reduce cost, term "design of experiments." stringent definition, quality improve­ cut product development time in I think Japan's secret weapon is ment is operating on the philosophy half, and achieve major competitive the company-wide, cooperative use that there is always a better way of market advantages.'" of a scientific approach to problem doing things. To find out how to do Taguchi methods undoubtedly solving. In particular, the scientific are applied extensively in selected thing~ better, we use simple scientif­ attitude as characterized by the industries, but data from Japan ic methods of data collection, data Plan-Do-Check-Action (PDCA) cir­ analysis, and experimentation as a provided by Professor Kusaba, cle, also known as the Deming Musashi Institute of Technology, and catalyst for our engineering and Cycle or Deming Wheel. Used the Japanese Union of Scientists other knowledge. An excellent intro­ throughout all organizational levels and Engineers (JUSE) seem to indi­ duction te; the fundamental and per­ and across all functions, in a spirit of cate that Taguchi's personal contri­ haps most powerful tools for quality genuine cooperation, this approach butions to quality engineering have improvement in manufacturing is is extremely powerful. When an Ishikawa's Guide to Quality Control, been applied only on a rather limited overall scientific attitude character­ basis in that country. In evaluating originally written for factory fore­ ized by the PDCA circle is adopted, the roie of statistical methods in men' The late Professor Ishikawa the seven tools and more advanced Japanese quality control, Kusaba describes what has become known statistical methods, such as design as the Seven Tools: check sheets, writes: of experiments, naturally present Pareto diagrams, cause and effect As regards the so-called Taguchi themselves as the tools for particu­ diagrams, histograms, stratification, method, the basic usage of the or­ lar jobs. scatter plots, and graphs. The seven thogonal array has been widely History of Industrial Applications tools and the spirit in which they are adopted since the 1950s as a type of Design of Experiments used by Ishikawa are simple appli­ of the design-of-experiment method. Although the seven tools have cations of a scientific approach to By contrast, its complicated usages played an important role in improv­ probiem solving. represented by the pseudo-factor ing quality in Japan, they are most Every process generates infor­ method, and the concepts of SN­ applicable to ongoing processes. To mation that can be used to improve ratio and on-line QC are the choice be more effective we need to start the process. 7 For example, when a of only a small number of people. the quality improvement effort up­ product fails it also produces infor­ The reasons are: 1) In spite of their stream at product design and proc­ mation (that it faiied and under what originality, these methods have not ess design. circumstances) that can be used to been provided with sufficient logical This need was recognized by find the cause for failure. In turn, explanation; 2) The usage of the the pioneers in quality control. One that information can be used to gain methods requires special skills; 3) of these was L. H. C. Tippett, who understanding of "why" the problem SN-ratio is effective in solving a lim­ worked for the British cotton indus­ occurs and to permanently fix it or ited range of problems, but the use tryon practical problems associated change the system. We therefore of logarithms makes it difficult to get with the manufacture of cotton prod­ need to "listen" to the process. But the physical meaning of the errors ucts from the mid 1920s and on­ to listen, we need "hearing aids" calculated, ordinary analytic tech­ wards. He had been exposed early such as control charts and the other niques are far simpler, have high in his career to the ideas of the Brit­ seven tools. testing power, and are effective ish statistician, Sir R. A. Fisher, The widespread and creative enough as well as convenient. 9 about design of experiments. Fish- Orthogonal arrays were invent­ ed in Great Britain by researchers

14 Target er's methods for effective experi­ year 70 7 7 4 75 10 77 7. ~ '81 82 83 84 ., 80 81 mentation, developed for agriculture, (Fu ) graph 29 16 19 18 19 15 26 36 26 20 40 40 44 59 70 88 55 78 were a fundamental break with the cause & effect diagI1ll11 UI6~1819~DY~~~~G~~4OD. tradition of only varying one factor at Pareto chart 6 7 10 9 12 2 10 22 17 21 18 20 23 33 36 34 34 40 a time. On the contrary, he recom­ histogxam 5 2 5 4 5 16 12 14 15 11 17 22 28 25 37 33 36 control chan 7 4 I 8 5 5 8 12 8 IS 11 20 23 26 21 23 20 13 mended varying all factors simulta­ scatter diagxam 3 7 3 4 12 IS 13 6 6 2 13 13 IS 24 22 neously in what is known as a facto­ process capability I 2 - I 141 2 7 - 3 nomogI1ll11S 2 4 - - - -' ---I-•- rial experiment. This method, and (General) the later developments of fractional design of cxpcrimcnt 18 8 14 13 IS 14 14 27 12 14 27 29 44 36 59 49 45 43 factorials and orthogonal arrays by correlation & re,eression 10 5 9 4 3 13 6 9 9 10 11 16 17 10 20 18 18 23 311 294462547 5 10 British, Indian, and American scien­ analysis ofvariance statistical test & estimation I 1 3 3 6 3 621 5 I I I 3 3 9 tists, provided great savings in ex­ optimization & EVOP I 1 I III 1 perimental effort. Fisher's method time series 2 12112 cumulative method 1 2 I 1 also provides more information sampling inspection -- 221 I 1 about the system studied than tradi­ (Multivariate Analysis) tional, one-at-a-time experiments. mUltiple regression . 3 2 3 3 5 2 4 3 5 12 4 5 17 12 14 23 13 8 prinCIpal componep.t analysIs . 1I 16I663478742 Tippett immediately saw the discriminant and cluster analysts ­ 12-1-2211411342 great potential for using Fisher's ex­ quantification theory ------45278 oth"" ---1---1 perimental design methods for im­ (Miscellaneous) proving the very difficult process of tree analysis & QFD· 3 6 6 30 29 42 18 14 43 32 40 transforming raw cotton of great var­ FfA - 11 8 14 10 18 iability to a final product (such as FMEA 2 6 5 3 10 - II 12 9 4 4 Weibull disttibution 3 I 1324321143723 dress shirts) where almost no varia­ distribution theory 3514535714 253 531 tion i6 allowed. Tippett wrote exten­ sensoI)' test 4 2 I 424 223 153 sively about the use of statistical relation chaIt 4 4 5 7 6 5 4 IS 7 6 PERT 2 2 4 2 1 1 132 methods in industry and his applica­ simulation 3 213 1 3 123 tions include, in addition to cotton computer technic & BOPS 2 6 6 1 10 industry examples, electricai, me­ oth"" 51I4211 242I24- 12 6 9 No. or Dresentanons 126 60 65 94 110 97 95 114 107 130 138 148 178 172 202 210 183 175 chanical, and foundry industry ex­ amples. He also taught short cours­ • QFD: quality function deployment chaIl es to people from a variety of Fig. t. Statistical Methods used in Presentations of Quality ControlAnnual Conference industries. A visionary paper written held in Japan, sponsored by Union of Japanese SCientists and Engmeers (JUSE). . in 1936 outlines in clear terms Tip­ Reproduced from Professor Kusaba's article,"Statistical Methods m Japanese Quality pett's broad view on the use of sta­ Control," Societas Qualitatis, Vol.2, No.2, May/June 1988. Note that several tistics for quality improvement. In methods sometimes were used in the same case study. particular, he pointed out that "The many outstanding papers on the ap­ Freeman,1O Professor of Statistics at need for the application of statistical plication of statistical methods to in­ MIT, who later wrote the book In­ methods to control of quality in in­ dustrial problems and in particular dustrial Statistics17 which includes dustry lies in the fact that all indus­ on the use of experimental design. several applications of design of ex­ trial products are subject to some During those early years, quali­ periments to industrial quality prob­ degree of uncontrolled variation."" ty experts and statisticians in the lems. Tippett was in close contact United States and Great Britain co­ At this 1938 conference Tippett with the work of Shewhart and reo operated closely. For example, the presented two very extensive lec­ fers often to Shewhart's books and Massachusetts Institute of Technolo­ tures 1B19 on the use of statistical papers. He must certainly have at­ gy (MIT) sponsored an Industrial methods: 1) "The Statistical PrincI­ tended Shewhart's 1932 lectures in Statistics Conference in 1938. ples of Experimentation, With Partic­ Great Britain organized by the statis­ Among the speakers were Dr. Wai­ ular Reference to Experimentation in tician Egan S. Pearson, another Brit­ ter A. Shewhart" from Bell Labs, Textile Factories," and 2) "Statistical ish pioneer in the area of quality and Leslie E. Simon,12 then captain Aspects of the Control of Quality in control. These lectures had great of the U.S. Army Ordinance Depart­ Textile Manufacture." These lec­ impact on the British audience and ment, and later general and author tures, which were subsequently pub­ led to the formation of the Industrial of the book An Engineer's Manual lished, show that design of experi­ and Agricultural Research Section of of Statistical Methods'" From ments was then considered an the Royal Statistical Society. They academia came the statistician S. S. integral part of statistical methods also led to the publication of the Wilks," Princeton University, who for quality control and improvement. Supplement of the Journal of the was very active in the area of engi­ Ten years later, after World War Royal Statistical Society, which in neering applications of statistics and II, Tippett was again invited back to the following decades published later co-author with J. S. Hunter and MIT to give a series of lectures. His I. Guttman of the book Introductory Engineering Statistics,15 and H. A. I>

Fall 1989 15 lecture notes are preserved in an 1950s to more effective industrial improvements or enhancements interesting book entitled Technologi­ product development. over other methods well-known to cal Application of Statistics, pub­ Design of experiments is vital in statisticians. 20 lished in 1950. About half of this new product development because Robust Product Design book is devoted to control charts time spent experimenting with proto­ Taguchi's important and useful and other process control-oriented types and debugging products and contribution is rather his engineering methods, but the other half is on processes often is prohibitive. West­ idea of robust product design and design of experiments for quality im­ ern industries, unfortunately, too parameter design. A robust car, for provement. often rush products into the market­ exampie, is a car that not only starts During the following decades. place without sufficient development and runs well under ideal environ­ Tippett and many other pioneers and testing, even relying on the cus­ mental conditions, but performs well successfully applied design of ex­ tomers to discover defects or mal­ even when the temperature is 110°F periment techniques and statistics in functions. This approach is signified and the humidity is 90 percent, or industry for reducing variation in by frequent recalls of defective when the temperature is -30°F and production processes and for devel­ products - the cost of which the the humidity is 0 percent. Thus ro­ oping better quality products. How­ consumer, of course, eventually has bust products are insensitive to ever, their efforts never received to pay. changes in uncontrollable conditions widespread industrial recognition in Efficient experimental methods or other kinds of variability. the United States and other Western are the basis for economically feasi­ We also use the term "robust" countries. The chemical and phar­ ble and thorough product develop­ about products that are insensitive maceutical industries are exceptions ment and testing as well as experi­ to production variation from nominal and design of experiments contin­ mentation aimed at improving values of the parts from which they ued to be practiced in agricultural production processes. Fisher's are assembled. This is important research, which was the area that method and later developments because when products are pro­ originally inspired Sir Ronald A. such as fractional factorials, orthog­ duced under mass production condi­ Fisher to develop the fundamental onal arrays, and response surface tions, the components invariably dif­ concepts of experimental design in methods constituted a major, but fer from their specified nominal the 1920s. Incidentally, Fisher was largely ignored, advance in modern values. If assembied products can urged to do this by his friend Gos­ manufacturing technology. The dif­ be made robust (insensitive) to com­ set, also known under the pen name ference between trial and error and ponent variation, production toler­ Student,21 who worked for one-at-a-time methods so common ances can be opened up, and that Guinness's brewery where he devel­ among Western engineers today, often means great savings in pro­ oped the first modern statistical and even the most rudimentary ap­ duction costs. methods out of industrial necessity. plication of Fisher's experimental de­ Taguchi's method for making It is curious that Western industry sign methods is truly dramatic. Fish­ products more robust is called Pa­ did not see the potency of design of er's methods are key ingredients in rameter DeSign. This method is experiments because many interest­ what have lately been described in based on the idea that the design ing examples were published in the the United States as "Taguchi meth­ parameters of a product can be ma­ forties, fifties, and sixties in Ameri­ ods." nipulated by experimental methods can journals such as Industrial Qual­ Taguchi has invented methods with the objective of finding product ity Control. Perhaps it was too easy such as signal to noise ratios, accu­ design configurations that are less to make a profit otherwise, and com­ mulation analysis, and linear graphs, sensitive to variation. Taguchi's best­ petition was not as tough as today. but it is experimental design that known example concerns the manu­ does the trick. Taguchi's own inven­ Taguchi Methods facture of tiles. Rather than buy a tions are not only inefficient in ex­ On the contrary, the Japanese new expensive kiln that would have saw very early the benefits of using tracting the available information less temperature variation, the Ina from often expensive and hard won design of experiments in the devel­ Tile Company of Japan experimen­ data, but are also more complicated opment of new products and proc­ tally found that by adding an inex­ esses. One of the best-known peo­ than methods which have become pensive lime additive to the clay, ple in this area is the engineer standard among Western statisti­ fewer tiles would break due to temp­ cians. Had his statistical methods Genichi Taguchi who for a long time erature variation in the old kiln. Thus been shortcuts used as alternatives worked for the Electrical Communi­ a simple cheap solution was found to more cumbersome but perhaps cation Laboratories in Japan."'" He Whereby the tiles were made robust successfully applied design of ex­ more correct methods, there would to temperature variation. periments and other statistical meth­ be no problem in recommending his Robust products and parameter ods he had learned from the United techniques. But the fact is that many design are important and very use· States and Great Britain in the early of Taguchi's statistical inventions are ful ideas. They should be included both more complicated and less effi­ as standard concepts used by all cient than mainstream statistical methods. Thus, his statistical inven­ tions can hardly be said to constitute

16 Target design engineers. Many expensive cluded in Taguchi's teaching. Most (DOE) has had no impact at all un­ efforts to improve process capabIli­ prominent among these omissions less modified for the Taguch/ way of ties may be unnecessary. Taguchi's are response surface methods. This thinking. concept is in sharp contrast to the is a set of techniques whereby the One of the tenets for quality conventional and expensive ap­ experimenter, in a step-by-step professionals is, "Let us talk with proach of reducing product variabili­ learning process, seeks optimal con­ data."27 In fact, the "27th Quality ty by controlling and eliminating ditions. This approach often means Control Conference for Foremen" causes of variability. Although the great savings in experimental effort, held recently in Japan had as its objective of this experiment was more surely leads to optimal condi­ motto "Make judgment according to Taguchi's useful notion of robust tions, and most importantly, leads to facts and act on the facts." Taguchi product design, the solution to the better engineering understanding of definitely has been able to create an problem in the Ina Tile example, as the system under study. In addition, unprecedented interest in the United many other examples of "Taguchi response surface methods are no States in design of experiments for methods," is a straightforward appli­ more complicated than "Taguchi quality improvement. For this inter­ cation of Fisher's method of fraction­ methods." est, we should be very grateful. But al factorial experiments. Part of the problem with the to claim that traditional design of ex­ Beyond Taguchi's Methods promotion of Taguchi methods is periments has had no impact is at To carry out parameter design that they are supposed to constitute best uninformed. Taguchi often recommends exp~ri­ "a separate technology."" That im­ An overwhelming collection of mental design plans, known as Inner plies that the user is asked to make published examples of successful and outer array designs. They are a choice between Taguchi methods applications of designed expen­ often wasteful in terms of the num­ and mainstream statistical methods. ments for quality improvement can ber of tests needed and hence are That implication is unfortunate be­ be found in the journals Industrial relatIVely expensive to conduct. For cause the statistical toolbox is very Quality Control, Applied Statistics, parameter design, he insists that large and contains many useful and Suppiement to the Journal of the signal-to-noise ratios be used for practical tools. What tool to use In a Royal Statisticai Society, Proceed­ analysis of the data. The more natu­ specific situation should preferably ings of the American Society for ral statistics, the average and the be determined by the problem at Quality Control, Electrical Manufac­ standard deviation, as well as a hand. Setting things up as mutually turing, Technometrics, Journal of the good homegrown "product," called exclusive alternatives, and advising American Statistical Association, Exploratory Data Analysis, pio~ , the user to choose Taguchi Meth­ Food Technology, Tooling and Pro­ neered by the American statisticians ods, leads to the dismissal of good duction, Biometrics, Journal of the John W. Tukey and Cuthbert Daniel, practical tools invented in the West American Society of Naval Eng/­ would be much better and also sim­ such as Cuthbert Daniel's Normal neers Journal of the Institute of Pe­ pler to understand. Exploratory data Plot technique." troleu'm, The Industrial Chemist, analysis is a collection of ideas Daniel's Normal Plot is a graph­ American Statistician, Chemical En­ about plotting and graphing data in ical method for analyzing data from gineering, Journal of the Society of ways that are informative and stimu­ unreplicated factorial experiments Plastic Engineering, Journal of lating for the engineer's intuition. -the kind of experiments used by American Leather Chemists Associ­ Nothing fancy-just a common Taguchi. In addition to being more. ation American Society for Testing sense application of the idea that a appropriate for unreplicated factonal Mat~ria/s Bulletin, Electrical Engi­ picture is worth a thousand words. experiments than the more compli­ neering, Analytic Chemistry, Rubber Using Taguchi's cumbersome and cated technique of Analysis of Vari­ Age, Tappi, Bell Systems Technical inefficient statistical methods is bet­ ance (ANOVA) favored by Taguchi, it Journal, Blast Furnace and Steel ter than doing nothing at all, but if is also extremely simple to apply Plant, Industrial and Engineering we have accepted the competitive and speaks directly to the right (intu­ Chemistry, American Society of Me­ challenge, why not use better and itive) side of the brain. chanicai Engineers Transactions, simpler mainstream statistical tools? The impression of exclusive­ Journal of Quality Technology, and For more details, see Box, Blsgaard ness is further promoted by mislead­ many others. The published exam­ and Fung." ing statements. For example, Sulli­ ples are, of course, just the tip of van" claims that: Industrial statisticians in the the iceberg. It seems hard to believe United States and Great Britain Traditional statistical theory has cre­ that people over a period of more have since the 1950s developed ated very little change in 30 years. than 40 years would continue to many usefuI and practical methods U. S. statistical specialists have publish examples that had "no im- for experimental design and data. been successful in maintaining the pact at all." .. analysis. These methods are not In- status quo for U. S. industries. In So why did Western statisti­ recent years there has been a mod­ cians in the past not succeed in get- est change in company operations through the application of statistical process control (SPC). However, traditional Design of Experiments I>

Fall 1989 17 ting a large number of engineers to informative analysis with more in­ proach, I do not mean engineering use design of experiments? And sight into the engineering problems based solely on deductive reasoning why was Taguchi more successful? involved. For an example, see the from predetermined theories, but "Quite simply, the Japanese have a analysis provided by Box" of rather an inductive-deductive ap­ secret ingredient: they do it and we Quinlan's" prize-winning experi­ proach based on iteration between don't. "7 That is the difference rather ment. This is because the design of theories, conjectures, and hypothe­ than any difference in technique. experiment principles used basically sis on the one hand and experimen­ And when they did it, they saw the are the same as mainstream prac­ tation, observation, and data analy­ benefits. The manufacturing environ­ tice. Both schools of thoughts are sis on the other.) ment is hectic (often because equip­ based on Fisher's method of factori­ Most of the industries that the ment and employee time are tied up al experiments. The primary differ­ United States is proud of are heaVily with the production of defects and ences lie in the subsequent data based on the interplay between sci­ rework). People are under great analysis. But why make that more ence and technoiogy. Science­ pressure to get products out of the complicated? In a time of serious based industries significantly contrib­ door. Like other applications of competitive problems for American ute to this country's economy and to "work smarter-not harder," experi­ industry it seems unfortunate to fol­ its foreign export. Moreover, the mentation for quality improvement low Taguchi's dogmas and discard most significant aspect of the mod­ means spending time up front but better and simpler alternatives. ern quality improvement approach is saving time and money later. West­ Science and Technology the scientific attitude to problem ern management is unfortunately There is also another more phil­ solving. This scientific approach ap­ forced to keep their eyes on next osophical difference between main­ plies even (in particular, one might quarter's revenue and therefore is stream quality control thinking and say) to the most mundane problems, not receptive to ideas that might that of Taguchi. Reading Dr. not only to "high tech" problems. By have a longer-term payback. More­ Deming's books and articles, for ex­ combining scientific knOWledge, sci­ over, the economic benefits of quali­ ample, one is struck by the scientific entific and experimental methods, ty improvement can be hard to heritage of his management theory. and developing new knowledge in quantify, or even be unknown and Taguchi, on the other hand, seems the course of developing new tech­ unknowable as Deming says.' Thus to claim that quality engineering is nology, manufacturers have devel­ 1believe the reason why experimen­ different from science. In a recent oped many commercially successful tal design methods were not used article, Taguchi writes: products. The scientific approach so much in the West in the past is was the driving force behind the in­ There is a great difference between unrelated to methodology, but in· dustrial revolution. The struggle to science and technology. Many peo­ stead because of the perceived understand "why" paid off hand­ ple have heard the story that business and the lack of under­ somely. Cooperation between scien­ "proves" that a horsefly can't fly, standing of the economic benefits of tists and engineers will bring us fur­ which hangs in the office of a weI/­ improving quality. Just as Deming ther prosperity and new technology known American corporate presi­ was not "discovered" in the West in the future. Ironically it is even the dent. Engineers have the responsi­ until the Japanese showed us the work of one of this century's most bility of designing things that benefit of quality management, so eminent scientists, Sir R. A. Fisher, function, whether or not it is possi­ did experimental design have to be that is the foundation for what has ble to prove why. 30 re-imported. Unfortunately it often been labeled Taguchi Methods. takes a crisis before the need for This argument might have some Taguchi's distinction between change is perceived. initial appeal because there clearly science and technology attempts to One of the advantages of ex­ are cases in industry, where a de­ set things up as alternatives, from periments based on Fisher's factori­ tailed scientific explanation is lacking which we have to choose the one or als, fractional factorials, and orthog­ or only partially possible with the the other, when in fact we can have onal arrays is that the conclusion current state of knowledge. Trying to both. Science and technology are often is so obvious that any method find a complete scientific cause and not alternatives; they are two inti­ of analysis would lead to the right effect explanation would sometimes mately connected and inseparable conclusion. This is the primary rea­ even be a waste of time and money. parts that by their interplay fuel son for the success of "Taguchi But equally often, engineers will find progress. methods." In fact, most of the case themselves stuck, unable to make further progress if they don't know Conclusion: We Have Only Seen studies of Taguchi methods pub­ the Beginning lished over the past years can be "why." Upon further reflection, I think most people will see that sepa­ Taguchi has had a tremendous analyzed with simpler mainstream impact on industry over the past few statistical methods providing a more rating science and technology is an unproductive approach. years. He has mobilized an unprec- (For clarification it should be pointed out that by a scientific ap-

18 Target edented interest among engineers With this approach we can develop 17 Freeman, H. A. (1942), Industrial Statis· for design of experiments and quali­ our own strategy for creating better tics, New Yorl<: John Wiley and Sons. quality products and services at " Tippett, L: C. H. (1938), "The statistical ty improvement. He has helped us Principles of Experimental Design, with focus attention on quality improve­ lower cost, become more competi­ Particular reference to Experimentation in ment and shown the economic ben­ tive, create more and better jobs, Textile Factories," in Proceeding of the In· efits of designing quality into prod­ and ultimately serve society better. dustrial Statistics Conference, New York: Pitman Publishing Corporation. ucts upstream rather than inspecting Quality improvement also applies to " Tippett, L. C. H. (1938), "Statistical As­ out bad products downstream. His the techniques we use, to their ex­ pects of the Control of Quality in Textile concept of robust product design, position, and to the principles for Manufacture," in Proceeding of the Indus­ parameter design, and the concept quality management." trial Statistics Conference, New York: Pit­ of loss functions to emphasize that man Publishing Corporation. References '" Tippett, L. H. C. (1950), Technoiogical Ap­ increasing costs are associated with , Juran. J. M. and Gryna, F. M., Jr. (1970), plications of Statistics, New York: John deviations from target values are Quality Planning and Analysis, New York: Wiley and Sons. valuable contributions to the science McGraw-Hili. " Gosset, W. S. (1958), "Sludent's" Collect­ of quality engineering. 2 Shewhart, W. A. (1931), Economic Control ed Papers, Edited by E. S. Pearson and John Wishart, Cambridge, UK: The Univer­ But as in any other science, of the Quality of Manufactured Product, New York: Van Nostrand Company. sity Press. many people make contributions. , Shewhart, W. A. (1939). Statistical Methoa " Taguchi, G., and Wu, Y. (1979). Off-Uno Ideas that pass the test of time are from the Viewpoint of Quality Control, edit­ Quaffty Control, Central Japan Quality added to the existing body of knowl­ ed by W. Edwards Deming, Washington, Control Association. edge. This way the quality of the D.C.: Graduate School of the Department " Taguchi, G. (1989), System of Experimen­ science and engineering disciplines of Agriculture. Reprinted 1986 by Dover tal Design, Volume I and II, White Plains, Publications, Inc. with new foreword by W. NY: UnipublKraus International Publica­ continues to improve, and ideas that Edwards Deming. tions. are not so useful are quickly forgot­ , Godfrey, A. B. (1986), "The History and " Box, G., Bisgaard, S., and Fung, C. ten. Rather than replacing traditional Evolution of Quality in AT&T," AT&T Techni­ (1988), "An Explanation and Critique of design of experiments and main­ cal Journal, Vol. 65, 2, 9-20. Taguchl's Contribution to Quality Engineer· ing," Quality and Reliability Engineering stream data analysis methods devel­ 5 Deming, W. E. (1986), Out of the Crisis, Cambridge, MA: MIT Press. .International, Vol. 4, 123-131. oped over the past 50-60 years with 25 6 Ishikawa, K. (1976), Guide to Quality Con­ Sullivan, L. P. (1987), "The Power Of Professor Taguchi's set of tech­ trol, New York: Unipub. Taguchi Methods To Impact Change In U.S. Companies:' Target, Vol. 3. 2. 18-22. niques, it would be better to add his , Box. G. E. P., and Bisgaard, S. (1987). useful ideas to current pracflce, to "The Scientific Context of Quality Improve­ 26 Box, G. E. P., Hunter, W. G., Hunter, J. S. ment" Quality Progress, Vol. XX, 6, 54-61. (1978), Statistics tor Experimenters, New use simpler mainstream statistical York: John Wiley and Sons. methods when availabie, to create B Eureka, B. (1987), "Explanation of Taguchi Methods and Quality Function Deploy­ ,., Ishikawa, K. (1985), What is Totai Qualfty appropriate new techniques where ment," as reported in Target, Vol. 3, 2, 19. Controi? The Japanese Way, Englewood Cliffs, NJ: Prentice-Hall, Inc. they are needed, and to retain the 9 Kusaba, I. (1988), "Statistical Methods in many useful mainstream statistical Japanese Quality Control," Societas " Box, G. E. P. (1988), "Signal to Noise Ra­ techniques that go far beyond the Qualitatis, Vol. 2, 2, Union of Japanese SCi­ tios, Performance Criteria and Transforma­ entists and Engineers. tions," Technometrics, Vol. 30,1,1-17. limited scope of "Taguchi methods." 29 Quinlan, J. (1988), "1985 Winner, Ameri­ 10 Tippett, L. H. C. (1936), "Application of We should take up the chal­ Statistical Methods to the Control of Quali­ can Supplier Institute Taguchi Application lenge from Japan and develop our ty in Industrial Production," Transactions of Award-Product Improvement by Application own strategy for quality improve­ the Manchester Statistical Society, 1-32. of Taguchi Methods:' Target, Vol. 4, 3, 22-29. ment. The Japanese did not just " Shewhart. W. A. (1938), "Application 01 '" Taguchi, G. (1988), "The Development 01 copy the early American methods Statistical Method in Mass Production" in Proceeding of the Industrial Statistics Quality Engineering," The ASI Journai, Vol. and ideas for quality control. They Conference, New York: Pitman Publishing 1, No.1, 5-29. took what they found useful and de­ Corporation. 31 The author wishes to thank the editor for veloped their own ideas too. We " Simon. L. E. (1938), "A Method of Ex­ many useful comments on a previous draft of this manuscript. This work was spon­ have only seen the beginning of pressing Quality," in Proceeding of the In­ dustrial Statistics Conference, New York: sored by National Science Foundation what can be done by combining sta­ Pitman Publishing Corporation. Grant DDM-8808138. tistical thinking, quality engineering, 13 Simon, L. E. (1941), An Engineer's Manual of Statistical Methods, New York: John and quality management. Just as Author: Wiley and Sons. the Japanese benefitted from listen­ Dr. S0ren Bisgaard is a professor in the ing to Deming, Juran, and Ishikawa, " Wilks. S. S. (1938), "The Rise of Modern Department of Industrial Engineering, Statistical Science," in Proceeding of the so can we. Clearly we should also University of Wisconsin-Madison, and Industrial Statistics Conference, New York: he is affiliated with the university's Cen­ listen to the useful engineering ideas Pitman Publishing Corporation. ter for Quality and ProductiVity Improve­ contributed by Taguchi. But we 15 Guttman, I., Wilks, S. S., and Hunter, J. S. ment. should apply the principle that "there (1971), Introductory Engineering Statistics, is always a better way of doing second edition, New York: John Wiley and Sons. things," rather than locking our­ o 16 Freeman, H. A. (1938), "Types of Statisti­ selves to a fixed set of methods. cal Methods Used and Problems Handled in Industrial Quality Control," in Proceed~ ing of the Industrial Statistics Conference, New York: Pitman Publishing Corporation.

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