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SPC is an ocean, capturing that in a one page nutshell is not a wise idea. Yet I have tried it in such a way that everyone atleast understands the conceptual idea of SPC. This article & seeing some more articles in our page will help everyone to understand SPC perfectly. I have seen SPC is practiced almost everywhere in a wrong way or just to satisfy the auditors, not to improve the process or product.

To emphasize the importance of SPC, we must know how the Japanese brought a quality revolution. In 1954, they invited quality gurus like W. Edwards Deming and Joseph M. Juran to help them improve their businesses. Japan becoming world no.1 in product quality is the result of the lectures given by two Americans W. Edwards Deming and Joseph M. Juran. Had Deming and Juran not given those lectures, Japanese goods would still be of stone-age quality.

These two quality gurus helped the Japanese to launch their quality revolution. The senior executives of Japanese companies took personal charge of managing quality. The companies trained their engineers to use statistical methods (SPC) for quality control & quality assurance. The companies enlarged their business plans to include quality goals. Each of these actions was unprecedented in industrial history. Together, they added up to a massive change in direction. Japanese companies evolved means of measuring customer satisfaction, competitive quality and performance that challenged the entire business community across the world. In contrast, CEOs of world’s leading companies had long been detached from the quality function. The image below shows renowned quality gurus & all of them are from USA & Japan. Why no quality gurus from India? It is because India’s businesses & its CEO’s are still detached from the crucial quality function, hence the seriousness of making quality as the no.1 priority is still not happening.

Here is the list of few things that we are using / used actively, yet will become obsolete soon or already obsolete, it is due to the quality revolution or the competitors have built better alternatives for these,

1. Shopping malls
2. Cash
3. Public telephone booths
4. Calculators
5. Paper maps
6. Print catalogues
7. Business cards
8. Parking meters (pay for parking cars)
9. House keys
10. Manual-transmission cars
11. College textbooks
12. Classroom chalkboards
13. Post boxes
14. In-person voting
15. Plastic shopping bags
16. Plastic, single-use straws
17. Car keys
18. Cheques
19. Desktop computers
20. Cursive writing
21. Remote controls
22. Fax machines
23. Stand alone GPS devices
24. Portable music players (iPod)
25. Sharing school photos
26. Print magazines
27. Alarm clocks
28. Headphones with cords
29. Hotel room keys
30. Landline phones (rotary or button telephones)
31. Compact Discs CDs
32. Paper receipts
33. Movies on DVD
34. Paper bills
35. Paper airplane tickets and boarding passes
36. Theatre tickets
37. Internet Explorer
38. 3G Phones
39. BlackBerry Phones
40. Encyclopaedias
41. Typewriters
42. Vinyl Albums
43. Film rolls
44. Answering Machines
45. Slide Projectors
46. Overhead Projectors
47. Phone Books (Yellow pages)
48. The Walkman
49. Floppy Disks
50. Bench Seats in Cars
51. Pagers
52. Calculator Watches
53. Minidisc
54. The Polaroid instant photo
55. Video Home System (VHS)
56. Dial-Up Modems

SPC helps businesses attain a profitable quantity & quality. SPC is like a horoscope of a person where the future can be predicted based on certain inputs in the present or past. I am 100% sure that most of the owners believe in astrology & vastu, like this if they believe in SPC, they can escalate their businesses to world class levels. Exactly this is what the Japanese did, i.e, believing in SPC that made them world no.1 in quality. It is important to quote about Mr.Aaron Levenstein (1913–86) who was an author and Professor of Business Administration at Baruch College. In one of his most memorable quotations he suggested that: Statistics are like a bikini. What they reveal is suggestive, but what they conceal is vital. Basically, he is saying that statistics can be used to confuse and mislead the reader. You can understand these when paid media or fringe groups post a poor picture about India & its economy by using irrelevant statistics. Hence it is advised to be careful while interpreting statistics. Do it the right way, if not, you will be trapped.

SPC depends on the process i.e, the manufacturing process (7m conditions). It does not depend on the specification or tolerance given by customers. A company that builds their manufacturing process to produce the products within 50% of the tolerance zone (w.r.t special characteristics) from midpoint makes profits straight away. Others suffer a lot. When NPD team (New Product Development) builds their product wisely like this, they are complying with all the four conditions mentioned in the “SPC-In A Nutshell” image straight away i.e, right first time (RFT) concept. For others, SPC will be like a roller coaster ride going through all the four phases as mentioned in the “SPC-In A Nuthsell” image.

“Out Of Control” situation due to Special Cause Variation

Instead of a factory example, I will take a hospital example to make you understand the four phases of SPC. The first phase is “Out of control”. You are visiting a hospital for a consultation after fixing an appointment over the phone. You have reached on time & expecting the waiting time for consulting will be less than one hour. Surprisingly on that day you are made to wait for more than 5 hours, being a specialist doctor who gives consulting only two days a week as well as you have undergone a major surgery there, you have no option other than waiting patiently. Being a six sigma person, you can clearly understand on that specific day some kind of “special cause” is disturbing the entire system of “doctor consulting his patients”. When I went through such a situation in a very famous hospital in Chennai, I started enquiring with the team involved in this process to understand what that special cause was. As it is a well built hospital with the entire needed infrastructure with adequate manpower, definitely the reason or cause for delay cannot be a “common cause”. Finally this delay or variation is due to a special cause, i.e, leave taken by that specialist doctor last week. Due to this all the previous week’s appointments were postponed to the next week, increasing the inflow of patients on that specific day. Expecting this increase they have made some arrangements like two consulting rooms with his assistants reading the status of the patients & doctor shuffling between two rooms & giving his decisions quickly based on the inputs from his assistants. Yet it was insufficient & the customer (the patient) can easily understand the “Out of control” situation. This is such a bitter experience which will remain in the memory of the patient, his attenders & his family for a lifetime.

Situation (or process) “In Control” as Special Cause Variations are identified & eliminated.

Causes (remember cause & effect or fishbone diagram?) are responsible for variation. A process is said to be “In control” when it has no special causes in it. Special causes are unanticipated, emergent, unpredictable, surprise, unexpected, non-quantifiable, and unusual. For the waiting time quoted in the “doctor consulting his patients” example, to bring it into SPC, the team involved in that process can build a chart by plotting “waiting time” of all patients. In our example case, the cause or reason is simple & visible; it may not be the same in all cases. Hence the team may be using control charts, cause analysis, capability studies to drive out or eliminate the special cause. Nelson’s 7 rules will help the team in understanding the presence of special causes, read our article on this title to know more about it.

Situation (or process) “In Control but not capable”

A process is said to be “In control” or “Stable” when all special causes are fully eliminated. A stable, in control process will have variations caused by “Common causes” only. Variations due to common causes will be due to the inbuilt / inherent variations present in the 6M Men, Machine, Material, Methods, Measurement, and Mother Nature. If the NPD team didn’t select the right combination of 6M conditions during the product / process development, the common cause variation will be more than the customer specification. So the situation or the process may be under control, but it may not be “Capable” as it doesn’t satisfy the customer requirements. Let us go back to our “doctor consulting his patients” example, there what is the customer requirement? You have reached the hospital on time & expecting the waiting time for consulting will be less than one hour. Hence the customer requirement is less than one hour. In our experience on that one specific day, the waiting time exceeded more than 5 hours. A special cause is a reason, which the hospital may avoid in future. I have visited the same hospital for consulting the same doctor 5 times & the waiting time is 1.5hrs, 1hr, 0.5hrs, 1hr & 5hrs. Out of these 5 incidents of waiting time, 3 times customer requirement was satisfied & twice it was not. Out of 5 incidents, once it was due to special cause, rest 4 incidents the variation that is range (max-min i.e, 1.5 – 0.5 = 1hr) 1hr is caused due to the “common cause” variation. Common cause variations are natural, predictable, random, constant, regular, inherent, inbuilt & measureable. To bring down this common cause variation that is 1hr of variation, some changes need to be made in the 6M conditions, mainly on the machines & processes. Apart from this, just think, how many hospitals or clinics you visit, ask you about what is your requirement w.r.t waiting time or how happy are you about their services? Aren’t we lagging in a huge way in building a quality culture?

Situation (or process) “In Control and capable”

This is the preferred situation. Special causes are eliminated & common cause variation operates within the 50% tolerance zone from midpoint of the customer requirements. Why 50% of the tolerance from midpoint? The midpoint is expected to shift or oscillate on both the sides due to no standard practices (sop), wear & tear, computer response time, poor working conditions, incompetent persons. Hence if the process is established to operate within 50% from midpoint, it will automatically take care of oscillations. Hence customer requirements will be always met & their expectations will be always fulfilled. In our “doctor consulting his patients” example, the patient’s waiting time will always be less than 1 hour. When the process is “In control and capable”, the team must monitor it meticulously through control charts to ensure the common causes always stay within limits & no special cause signals are noticed. To monitor this team must select the right control charts relevant to their operations, reading our article on “Popular control charts – In A Nutshell” will help you to understand how 8 types of control charts can be used extensively for all kinds of situations.

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Thanks & Regards,

Devarajan NR,
Chairman – JBEGlobal.com Job Portal & IATFTrainingPortal.com (Since 2013) Past – Delphi TVS | Rane | Brakes India | Iris Mfg. (Shriram Group) | Hinduja Foundries | IRS (IRQS) | 9362439124 | devarajan.jupiter@gmail.com