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6 Sigma is a methodology for statistical analysis of data created in the 1980s by Motorola. 6 Sigma is a suite of statistical tools used to reduce process variation.


From the launch of the 6 Sigma project, the first step is to define and structure the Voice Of Customer, Voice of the Customer . The VOC represents what makes the product or service good from the customer’s point of view and corresponds to the customer’s needs analysis

Step 1 : Identify the customer

It is necessary to identify the customer (s). There are 3 types of customers1 :

  • Internal customer : shareholders, project sponsor, management and downstream process…
  • Intermediate Customer: Businesses, Distributors, Retailers, Buyers, Subcontractors n+1…
  • End customer: end users.

The question of who is the customer? ” is essential. We must not neglect a category of client. For example, even if the end customer is very satisfied with the product, but the retailer does not want to put it on their shelves, the product will never reach the end customer.

Although Philips is convinced that simpler programming is better for its customer-user, it is blocked by the reluctance of distributors whose salespeople are very familiar with old systems.2.

Step 2: Collect the Critical To Quality

This is to collect the expectations of customers previously identified. Depending on the type of project and its scope, this step will be done with the support :

  • Marketing and sales representatives if the scope of the project exceeds the company (intermediate or final client)
  • With methods, purchases and other support services if the client is internal.
Studies show that the customer is the source of the greatest number of ideas and not the salesperson, leading … 2 . In addition, the interest in harvesting the VOC is not only to improve the negative points but also to look for the implicit, latent, or not expressed expectations 3 also called waiting potential4.

Definition of the Critical To Quality

Critical To Quality are the attributes of a product, service or process to achieve customer satisfaction. By definition, an attribute consists of a feature to which a means is assigned (example: the function “lift the window” associated with the means “electrical control”).

The typologies of need

There are 4 different types of customer expectations:

  • expressed : It is a need made known to all in a direct way by the customer. The customer expresses what he wants, what he expects.
  • Implicit : The customer is not aware of it. This explains the reason why it is not expressed. Identifying and satisfying it creates a great customer satisfaction.
  • Aroused : These are the needs that are not inherent to the customer but that are aroused by those around him, a salesman … For a company, the levers of action are the communication, the marketing and the training of the salesmen..
  • Imposed : The imposed needs are dictated by norms, regulations, unspoken rules … Responding to them may be mandatory or be an important strategic factor.

Notion of incremental and iteration


The iteration is subtle, the need is only implicit. We will draw the contours of our product then by successive iteration with the customer, we develop the good product.


Overall, the customer knows his need. We will then make different evolutions of our Products / Services.

Collection of information

Collection methods

Focus group**

Individual interview**

Empathic conception

Observation on purchase

After-sales service and complaint


Meeting with 6 to 12 customers

Interview with 1 customer

Customer test

Observe directly on the place of purchase the process.

Analysis of letters, complaints…

Quality of information













*For example, the teams of Toyota Industrial Vehicle (forklift …) did not hesitate to go to Norway, to analyze their customers, considered, by the difficult climate, as Lead User. Toyota was able to change cables (existing on the Yaris), which did not resist the cold, and was able to spread the solution throughout its range.

Focus-Group / Individual Interview Comparison

**The graph below compares the effectiveness of the focus group and the individual interview. This graph shows that 2 individual interviews are slightly more effective than a focus group (51% vs 50%), and that 4 individual interviews are more effective than 2 focus groups (72% vs. 67%). But the relative cost of 2 or 4 individual interviews is lower than 1 or 2 focus groups of 6 to 8 people7.

Evolution of the percentage of expectations collected / number of people surveyed

The results of a study show 8 that the interview of 20 to 30 people in the same segment can identify 80 to 90% of total expectations.

Source : A. Griffin, J. R. Hauser (1993) – The voice of customer

The difficulties of collecting

  • Customers all want something different11
  • They do not know what they want or what they need12,13, 14,15
  • They do not always buy what they need
  • They do not always buy what they want or what others believe they want
  • They are always waiting for more
  • They are influenced16

Step 3 : Sorting customer expectations : the CTQ tree

Customer expectations« grosst » are difficult to treat. Some are too precise and others too general. To facilitate the processing of these data, it is a question of organizing them in the form of affinity diagrams via the KJ method17,18.

  • Emphasize in red the implicit elements. This will make it possible to judge at once whether the level of reliability of the tree.
  • Use the Verbatim directly to avoid interpretations and posterior judgments

Step 4 : Prioritize CTQ

Basic methods

Advanced methods

Ascending or descending order

Paired analysis

Basic notation (1 to 5, 1 to 9…)

Analytical Hierarchy Process

Verbal expression (satisfactory, mediocre…)


Difficulties of prioritization

  • Lack of information19
  • Too many things to compare
  • Diverging opinions in the group
  • Impossible estimates
  • Arbitrary results

Customer satisfaction, above all a story of behavior

Go see and exchange directly with the customer

Work in an integrated way with the customer

Validate the actions gradually

Put yourself in the customer’s shoes and use the products

Take all customer returns and complaints seriously



1 – L. R. Guinta, R. N. Praizler (1993) – The quality function deployment book : the team approach to solving problems and satisfying customers through QFD

2 – J. P. Deschamps, P. N. Ranganath (1994) – Les maîtres de l’innovation totale

3 – C. Kliewer, E. Liu, D. Stephen, D. Weening (1998) – Quality function deployment

4 – M. G. Vigier (1992) – La pratique du Quality Function Deployment

5 – C. Hepner-Brodie (2000) – Invigorating strategy with the voices of customer

6 – D. E. Leaonard-Barton, E. Wilson, J. Doyle (1994) – Commercializing technology : imaginative understanding of user needs

7 – E. Dahan, J. R. Hauser (2001) – Product development – managing a dispersed process

8 – A. Griffin, J. R. Hauser (1993) – The voice of customer

9 – S. Shiba, A. Graham, D. Walden (1993) – A new american TQM, four practical revolutions in management

10 – R. Tourangeau, L. J. Rips, K. A. Rasinski (2000) – The psychology of survey response

11 – B. Avishai, W. Taylor (1989) – Customer drive a technology driven company : an interview with Georges Fisher (President Motorola)

12 – G. Dounes, M. Geoffroy (2005) – Ipod Backstage

13 – J. A. Shumpeter (1951) – Essays

14 – W. C. Kim, R. Mauborgne (2005) – Stratégie océan bleu

15 – C. Midler (1993) – L’auto qui n’existait pas

16 – E. Dahan, J. R. Hauser (2001) – Product development – managing a dispersed process

17 – J. L. Bossert (1991) – Quality function deployment, a practitionner’s approach

18 – W. E. Eureka (1987) – Introduction of quality function deployment

19 – B. Yannou, F. Limayem (2002) – Méthodes de comparaisons par paires pour la pondération en groupe


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