Scholarly article on topic 'The Role of Early Prototypes in Concept Development: Insights from the Automotive Industry'

The Role of Early Prototypes in Concept Development: Insights from the Automotive Industry Academic research paper on "Materials engineering"

Share paper
Academic journal
Procedia CIRP
OECD Field of science
{"New product development" / "product engineering" / "fuzzy front end" / "physical prototypes" / "robust design"}

Abstract of research paper on Materials engineering, author of scientific article — Christer W. Elverum, Torgeir Welo

Abstract The early phases of new product development have become an area of increasing research interest during the past decades. The vast majority of researchers agree that the potential for the most substantial impact on the innovation outcome lies in the execution of the early phases. In this paper, the early phases of the new product development process in seven automotive OEMs is studied. The present work discusses in general terms the findings from the sample of companies, as well as two in-depth reviews of recent product innovations launched by one of the OEMs; using semi-structured interviews. In these case studies, prototypes were identified to play a particularly important role with regard to: 1) enabling the team to explore various concepts and reduce (mainly) technical uncertainty, 2) communicating and gaining (financial) support from internal decision makers and 3) providing detailed characteristics in order to gain a deeper understanding of the product requirements. Based on these findings, it is concluded that the role of prototypes as enabling tools for innovation outcomes is just as important in the early product development phases as in the more commonly explored late phases.

Academic research paper on topic "The Role of Early Prototypes in Concept Development: Insights from the Automotive Industry"

Available online at


Procedia CIRP 21 (2014) 491 - 496

24th CIRP Design Conference

The role of early prototypes in concept development: insights from the

automotive industry

Christer W. Elveruma*, Torgeir Weloa

aRichard Birkelands vei 2B, Trondheim, 7491, Norway

Corresponding author. Tel.: +47 928 40 643. E-mail address:


The early phases of new product development have become an area of increasing research interest during the past decades. The vast majority of researchers agree that the potential for the most substantial impact on the innovation outcome lies in the execution of the early phases. In this paper, the early phases of the new product development process in seven automotive OEMs is studied. The present work discusses in general terms the findings from the sample of companies, as well as two in-depth reviews of recent product innovations launched by one of the OEMs; using semi-structured interviews. In these case studies, prototypes were identified to play a particularly important role with regard to: 1) enabling the team to explore various concepts and reduce (mainly) technical uncertainty, 2) communicating and gaining (financial) support from internal decision makers and 3) providing detailed characteristics in order to gain a deeper understanding of the product requirements. Based on these findings, it is concluded that the role of prototypes as enabling tools for innovation outcomes is just as important in the early product development phases as in the more commonly explored late phases.

© 2014 Publishedby Elsevier B.V.Thisis an open access article under the CC BY-NC-ND license (

Selectionandpeer-reviewunderresponsibilityof thelnternational Scientific Committee of "24th CIRP Design Conference" in the person of the Conference Chairs Giovanni Moroni and Tullio Tolio

Keywords: New product development; product engineering; fuzzy front end; physical prototypes; robust design

1. Introduction

1.1. Background

New-product development (NPD) performance has become an area of growing research interest during the past decades. Innovation outcomes and the ability to differentiate from the competition in an increasingly saturated, global market are closely related to the effectiveness of NPD practices. The focus has for a long time been on the NPD process as a whole. However, in the late 1980s the focus started shifting to the earlier phases of NPD and Cooper was one of the first researchers to identify and argue for the importance of the early phases and found a strong correlation between "pre-development" work and product success [1].

In 1991, Reinertsen and Smith coined the term "the fuzzy front end" (FFE) for describing the early phases of NPD [2]. In the following years a considerable amount of research has been conducted to gain further understanding of the

implications of the FFE and the associated factors for achieving market success.

The field of FFE research remains characterized as young and exploratory and there is an on-going discussion f whether a structured approach similar to that of the late stages in the NDP or a contextual approach is most appropriate for achieving FFE success. Authors such as [3-7] opt for a more structured and linear model while others argue that there are no universal models due to the importance of context [8-13]. Despite the disagreements on the approach, the FFE remains an important part of the NPD that needs further investigation to be fully understood. Husig and Kohn [14] argue that the future FFE research challenges can be found on a more micro level, such as individual projects.

1.2. The automotive industry

The automotive industry is a mature, ultra-competitive industry that has focused on refining its production and

2212-8271 © 2014 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of the International Scientific Committee of "24th CIRP Design Conference" in the person of the

Conference Chairs Giovanni Moroni and Tullio Tolio


product development systems for decades. A considerable amount of methodologies, philosophies and tools stem from the automotive industry, such as lean manufacturing and lean product development. Development processes have in large parts been formalized and structured to be able to bring increasingly more complex and refined products to the market at an affordable price and with high quality. To be able to discuss the FFE and the subsequent phases it is necessary to go more into detail on how the organizational structure and development of new products is typically carried out in the automotive industry.

It is well-known that it is necessary to innovate in order to achieve long-term success. At the same time, for short-term success and keeping up with the competition it is necessary to develop and launch incrementally better products such as successors of existing vehicle models. In order to ensure a steady stream of incrementally improved products while investing for long-term success, it is common to separate these activities into two different "buckets". Thus, the more risky and exploratory tasks are commonly separated from more straightforward incremental development. This allows the more risky development and research projects to be managed in a different way than incremental development projects, thus leaving more room for experimentation and testing.

The more strategic development tasks are traditionally conducted within research and advanced engineering departments. A new technology often starts out within research and is transferred to advanced engineering when it reaches a certain readiness. Advanced engineering then develops the technology to the point where it is sufficiently mature and ready to go into a vehicle program. The technology is then kept "on-the-shelf" until found attractive for a certain program. This is sometimes referred to as shelving technology or "putting the technology in a refrigerator" [15, p. 8].

Most major OEMs have various departments that focus on early concepts and the application of new technology. Several of these departments are located in the Silicon Valley and the Los Angeles area. These departments are mainly focused on technology scouting and early development of advanced technologies and concepts. The concepts developed at these departments are either killed off or transferred to other parts of the company for further development, e.g. advanced engineering. The figure below depicts a typical sequence of development. Here it should be noted that this is a very simplified illustration, whose only intention is to provide the reader with a rough overview of the role of the various departments within the organization along with their role in the development of new products and technologies.

Fig. 1. Overview of typical concept development sequence.

2. Literature review of prototypes in brief

Prototyping has always been an important tool for designers and engineers. The majority of reported research explicitly addressing prototyping is within the field of software engineering, particularly human-computer interaction (HCI). However, this does not necessarily imply that the origins of prototyping as an activity stems from the software environment. According to Ullman [16], the method of quick and small releases and subsequent fixes that has become popular and considered state of the art within software development stems from the early days of mechanical engineering: the time when something would be tried, broken, fixed, and tried again. '[16, p. 116]. Although prototyping has been recognized as an important tool in the engineering and design of physical products, it is almost absent from most state-of-the-art theoretical design models.

Prototyping is generally recognized as a verification tool in product engineering, thus it is considered to play an important role in the late stages of the NPD process; typically serving as a demonstrator to determine if the product is ready to move into the production stages. In software development, particularly within HCI, prototyping has a far more integrated role in the development process. Here, prototyping is used in the early phases to explore various possibilities and to determine requirements and drive the development forward through iterations. However, when taking a closer look at research conducted on the early stages of new product development, several researchers have found the use and importance of prototypes to be substantial.

In a study of 553 Japanese mechanical and electrical engineering companies, Herstatt, Stockstrom [17] found that over 90 % of the companies make use of early physical prototypes and 15 % perform rapid prototyping. In the same study it was also found that to incorporate the voice of customers it is common practice to present virtual or physical prototypes to potential customers. Reinertsen [2, 11] describes the use of prototypes in the early phases and argues for prototyping the parts of a product or a system to reduce uncertainty, as well as developing several low-cost prototypes in the early stages to ease the concept selection. Quinn [18] found that due to inadequacy of theory, innovative enterprises seem to move faster from paper studies to physical testing. Additionally, whenever possible they allow several prototype programs to proceed in parallel.

The findings are even more compelling for the development of novel products. Veryzer [19] investigated several radical innovation projects and found that in all cases the firms developed prototypes at an earlier stage than in the typical, incremental NPD process. Prototype building in these projects preceded opportunity analysis, assessment of market attractiveness, market research and financial analysis. Srinivasan, Lovejoy [20] propose a new approach to reconsider the concept selection stage in the NPD process. They argue that it is necessary to carry multiple concepts forward into "customer-ready" prototypes before choosing a particular concept for commercialization. A "customer-ready" prototype in this case means a prototype that is similar to a final product, both in terms of appearance and function, but typically manufactured with more flexible manufacturing processes.

3. Scope

The findings above indicate that prototyping is an essential activity in the field of product engineering, and even more so in the case of novel products. What this research does not explain is how organizations make use of the activity of prototyping and the prototype artifacts.

The rest of this work focuses explicitly on prototyping and aims to provide the reader and the research community with recent insights on prototypes and prototyping from specific cases within the automotive industry.

It should be noted that prototypes and prototyping constitutes only a fraction of the tools and activities in the front end, and it is important not to undermine the importance of other aspects of the FFE.

4. Method

This paper is based on a comprehensive literature study of FFE research, automotive research and prototyping research. In addition to building on former research the research strategy includes semi-structured interviews with thirteen employees from seven major automotive OEMs as well as two in-depth historical reviews of recently launched products by one of the OEMs. There are several reasons for choosing a qualitative approach in this study. Firstly, the field of FFE is relatively young and unexplored, thus it is necessary to rely on an open-ended explorative approach to gain insights on unknown problems and challenges. Secondly, the context in which the organizations operate is believed to be of major importance, as indicated by other authors [12-14, 21]. This real-world setting and the importance of context is difficult to capture with a quantitative approach and qualitative approach is favorable [22].

Employees from various departments in the organizations have been interviewed. The sample can be divided into two main parts:

• Front-end satellite departments of the OEMs located in


• Research and advanced engineering at the main locations

within the organizations, located in Germany and the

Detroit area

The select front-end departments vary considerably in terms of roles and area of expertise. Some departments deal with holistic vehicle design and entire concept cars, while others are solely focused on connectivity and entertainment. For the sake of simplicity, in the continuation these departments will collectively be referred to as front-end departments.

In addition to interviews concerning general challenges and success factors in the early stages of the FFE, two innovations from one of the OEM were studied in-depth to gain further insights into the FFE as well as the connection between the work performed in the FFE stage and the later stages.

Details and an overview of interviewees are provided in Table 1. For confidentiality reasons, the OEMs and the interviewees chose to stay anonymous.

Table 1. Overview of interviewees.

Company Interviewees

Code Department_Position

A Front-end department Business manager Director concept R&D

B Front-end department Design engineer

C Front-end department Research manager

D E Vehicle pre-development and research and advanced engineering Vehicle pre-development Vehicle engineering manager EV dimension architect Company PhD candidate

F Features & Technology Planning Director features & technology planning

G Front-end department Project manager R&D Project manager R&D Advanced PP manager

5. Results

5.1. Findings from FFE practices

The interviews with the automotive OEMs focused on general aspects of the FFE, including e.g. working structure, concept transfers, challenges and success factors. For a summary of the findings see Elverum, Welo [23]. Among the eleven interviewees, the majority reported that using physical prototypes was one of the most important and effective tools in their early concept work.

One of the main findings was that the most effective method for convincing internal decision makers as well as external clients such as suppliers was through extensive use of prototyping. Since the front-end departments are satellite departments, which are separate from the core of the organization, they are often faced with the challenge of selling concepts internally within the firm. Thus, several stakeholders need to be convinced in order for the project to get funding to proceed into further development. Furthermore, the prototypes serve as a platform to facilitate communication externally and within the team.

The majority of the interviewees reported that the display and demonstration of a physical prototype is the most effective way to convey a concept. All of the front-end departments relied strongly on physical prototypes to influence the decision of whether or not to continue development.

Considering the (less fuzzy) vehicle pre-development stage, however, a stronger reliance on computational tools was found. A possible explanation for this finding is that the technical risk at this point is rather low and firms have extensive knowledge and experience from developing previous vehicle models. The solution space is well-known and large databases concerning the performance and relationship between various components can be utilized. Furthermore, physical prototyping at this stage is generally capital intensive and time-consuming.

One of the front-end departments sketched out three different strategies used to convince or influence internal and external stakeholders when proposing new concepts. Typically a combination of the following elements is used:

• Physical prototype

• Videos - mock-up scenarios or video of prototype if people cannot be physically present

• PowerPoint slides, diagrams, rationales, etc.

The interviewee did also state that physical prototypes worked best, in particular high-fidelity prototypes.

Three of the departments emphasized that contextualizing the concept is of great importance. This means to place the concept in a larger context, in its natural environment and typically in interaction with potential users and usage scenarios, which is in line with the findings of other researchers such as [24]. As stated by one of the interviewees 'There is a need to sharpen the fuzziness through the customer lens'. Abstraction and "fuzziness" is reduced through building a story and a customer around the concept. This helps the team focus on achieving a common goal as well as communicating the value of a project to internal stakeholders and making the project known throughout the organization.

These more general findings associated with the FFE led to the study of two specific products that started out as bottom-up ideas in the engineering community at one of the OEMs. The concepts continued through the development process and were finally launched as products in the marketplace. The overarching goals and focus in these studies were:

• To understand and map out the entire development process for each of the two products, from initiation to implementation and the industrial context they were developed in

• To focus specifically on prototypes and identify what kind of prototypes were developed in each stage of the process and how they influenced the decision making

5.2. Case A - inflatable seatbelt development

The first case concerns the development of a new-to-the-world product: an inflatable seatbelt (for high-volume applications). This was a particularly challenging project, both from technical and usability standpoints. The technical solution had never been developed before and turned out to be quite challenging. The customer-user interface was another critical aspect: even if the product reduces injuries during impact—it is of no use if customers find the seatbelt uncomfortable and choose not to use it. Therefore, one of the key requirements throughout the entire project was that the inflatable seatbelt should look and function similar to a regular seatbelt. It should be comfortable and aesthetically pleasing.

As Hall [25] states, requirements are a function of both the context in which the product is used as well as of the particular task to be performed. In this project, the particular task to be performed was relatively easy to define and test for. However, testing for the context in which the product is to be used was much more challenging. Since the product was a safety device all possible scenarios and ways the users will interact with the product had to be identified and tested. In this regard, physical prototypes helped uncover and test

for scenarios that were impossible through the use of digital tools alone.

Early concept stage

In the early stages, prototypes were mainly used to understand the concept. Does it work? How does it work? Why does it work? As stated by one of the interviewees, early prototypes are critical: '... we do need early prototypes to understand this, even within the team'. The early concept prove-out prototypes were rough, "cobbled up" ones that mainly aimed to determine if the system has any positive effects during a crash. The prototype was tested in a standard sled test with crash test dummies and turned out to be highly effective. One of the interviewees mentioned that early sled tests achieved the initial targets set by the team and concept prove-out was completed in a year and a half. The collected data made the team believe in the technology and the project was given financial support.

Prototypes to gain internal support and overcome design challenges

After the concept prove-out was successful, the work towards a more refined product began. This phase of the development turned out to be far more challenging than the technical concept prove-out. There were several problems related to the usability of the product. The initial placement of the gas inflator was problematic and caused ergonomic issues, the initial design is pictured in Fig. 2. The team tried several alternative solutions with no success. The problem slowed the entire project down and a less desirable system design was considered as an alternative. At a relatively late stage in the project a few team members came up with a radical idea: running the gas from the inflator through the belt buckle. However, this idea went against the entire industry's way of designing a buckle, thus the idea met a lot of resistance. Everyone said that this could not be done, that this design would never work.

Despite the resistance, three members decided to work on the alternative of feeding gas through the buckle. This led to an initial design that was 3D printed in plastic using stereolithography (SLA) technology. With this simple and rough prototype the members were able to convince the rest of the team that this solution could work, and the work towards functional prototypes began. As stated by one of the interviewees, physical prototypes are effective tools to advocate for a concept: 'So a physical prototype at the concept level is the best tool I've found to overcome the emotional barriers of the various, we call them stakeholders. So the marketing, manufacturing, engineering, management and organizations is one. the early prototype was successful of overcoming barriers any amount of PowerPoint presentations and computer analysis'

Prototypes and testing to understand Failure Mode Effect Analysis (FMEA) and product requirements

Later in the project, prototypes were important to understand, explore and test for the various FMEA. This finding is in line with the argument of Ulrich and Eppinger [26] for using physical prototypes—that is—physical prototypes are required to detect unanticipated phenomena.

Fig. 2. Exploded view of the initial inflatable seatbelt concept.

One reason for this is that 'all of the laws of physics are operating when the team experiments with physical prototypes' [26, p. 298]. Even the early concept prototype in this example proved to be invaluable in that sense. The interviewees reported that one of the huge advantages to early conceptual prototypes is that you can see the unintended consequences and the system interactions. Certain scenarios are determined in advance and the prototype is then used to come up with other scenarios. One effective way is giving the prototype to a customer and letting them play with it.

5.3. Case B - panoramic roof module development

This product is substantially different from the inflatable seatbelt, and the prototypes played a different role in this case. The product is a technological improvement over the existing product and the context in which the product is used is more easily identifiable.

The project started with two engineers discussing the panoramic roof modules on the current vehicles offered by the company. They had ideas for improving the current design in several ways. Instead of using large stamped steel parts (see Fig. 3), the new design utilized complex aluminum extrusions (see Fig. 4 b). This would reduce the weight and make the product more flexible so it could be re-used for other vehicle models.

The biggest hurdle in this case is that the OEM does not make roof modules; they are both designed and produced by an external supplier. Thus, there were few incentives and support within the company to spend resources aimed at improving the product. In order to increase the probability of implementation on a production vehicle, the team decided to build, test and verify a comprehensive and fully functional prototype.

Early concept stage

Before the project officially launched, it was of utmost importance to determine if an aluminum structure could replace the current steel structure. CAE/FEA simulations were used to answer this question and acted as the main decision criterion in a go/no-go gate.

After the simulations confirmed that aluminum alloy extrusions could provide the desired characteristics, two critical functional prototypes were made. The two questions to be answered with these prototypes were related to technical feasibility; is it possible to extrude this complex profile? If yes, is it then possible to maintain the cross section

of the extruded profiles (within certain dimensional tolerances) after bending them to the curvature of the vehicle?

Persuading/convincing decision makers

Once the two critical functional prototypes confirmed that it was possible to manufacture the parts within required capability requirements, the team started working on designing the roof module. The final outcome was a fully functional comprehensive prototype that was installed on several vehicles and tested in the laboratory, see Fig. 4a. Once the benefits of the new design were confirmed, the team presented the product to product development and management for evaluation of possible implementation in a production vehicle.

Fig. 3. Original steel roof module.

Fig. 4. (a) final prototype of new design; (b) cross section of extrusion. 5.4. Discussion of overall findings

The findings in the two in-depth cases and the sample of front-end departments provide some insights on the activity of prototyping and the use of prototypes within the automotive industry.

A common denominator from all the interviews is that prototypes serve as tools for communication, both within the team and externally. Even simple physical prototypes are found to be powerful in influencing various stakeholders. This is a phenomenon that needs to be further studied to understand how physical models influence decision-making. Most teams and individuals are faced with the need to "sell" their ideas within the organization and innovative new concepts and opportunities are of limited value to an organization if they fail to proceed beyond the idea stage. Kim and Wilemon [27] refer to this as a type I error: to reject an idea when it is a possible success. In this regard, physical artifacts might serve as a common platform for communication across disciplines and organizational roles.

Another finding that is worth noting is related to types of prototypes and the newness or unfamiliarity with the concept. In Case A, the making and subsequent testing of a physical prototype acted as a go/no-gate and preceded

analytical prototypes. Whereas in Case B an analytical prototype preceded the building of a physical prototype.

6. Conclusions and outlook

The present case studies within the automotive industry reveal that prototyping plays various roles at each stage in the development process. At the early concept level the prototypes serve as a common platform for communicating and understanding the concept within the team and for external stakeholders. In later stages, the prototypes provide context in order to understand product requirements. Users are set in contact with a prototype to uncover and come up with scenarios of use and misuse, thus increasing the robustness of the design.

The findings in this paper are limited to seven companies within the automotive industry, and future research should expand to other types of industries and perhaps consider studies involving a broader sample and quantitative methods to obtain more concrete data.


The authors would like to thank the employees at the seven automotive OEMs for taking the time to participate in this study and the research program SFI Norman along with The Research Council of Norway for financial support for carrying out this research.


[1 ] Cooper RG, Kleinschmidt EJ. New Products - What Separates Winners from Losers. J Prod Innovat Manag 1987 Sep;4(3):169-84.

[2] Reinertsen DG, Smith PG. The strategist's role in shortening product development. J Bus Strategy 1991;12(4):18-22.

[3] Khurana A, Rosenthal SR. Towards holistic front ends in new product development. J Prod Innovat Manag 1998 Jan;15(1):57-74.

[4] Khurana A, Rosenthal SR. Integrating the fuzzy front end of new product development. Sloan Manage Rev 1997 Win;38(2):103-20.

[5] Smith GR, Herbein WC, Morris RC. Front-end innovation at AlliedSignal and Alcoa. Res Technol Manage 1999;42(6):15-24.

[6] Verganti R. Leveraging on systemic learning to manage the early phases of product innovation projects. R&D Manage 1997;27(4):377-92.

[7] Flint DJ. Compressing new product success-to-success cycle time -Deep customer value understanding and idea generation. Ind Market Manag 2002 Jul;31(4):305-15.

[8] Breuer H, Hewing M, Steinhoff F. Divergent Innovation: Fostering and Managing the Fuzzy Front End of Innovation. Proceedings of Picmet 09 - Technology Management in the Age of Fundamental Change, Vols 1-5. 2009:744-51.

[9] Chang HW, Wei CC, Lin RJ. A model for selecting product ideas in fuzzy front end. Concurrent Eng-Res A 2008 Jun;16(2):121-8.

[10] Corallo A, Lazoi M, Merotto R, Secundo G. Enhancing Knowledge sharing in Fuzzy Front End of NPD: An Aerospace Case Study. Proceedings of the 11th European Conference on Knowledge Management, Vols 1 and 2. 2010:288-95.

[11] Reinertsen DG. Taking the fuzziness out of the fuzzy front end. Res Technol Manage 1999 Nov-Dec;42(6):25-31.

[12] Reinertsen D. Streamlining the fuzzy front-end. World Class Design to Manufacture 1994;1(5):4-8.

[13] Nobelius D, Trygg L. Stop chasing the Front End process — management of the early phases in product development projects. Int J Proj Manag 2002 July 2002;20(5):331-40.

[14] Hüsig S, Kohn S. Factors influencing the front end of the innovation process: A comprehensive review of selected empirical NPD and explorative FFE studies. 10th International Product Development Management Conference; 2003 June 9-11; Brussels, Belgium.

[15] Magnusson T, Lindström G, Berggren C. Architectural or modular innovation? Managing discontinuous product development in response to challenging environmental performance targets. IJIM 2003;7(01):1-26.

[16] Ullman DG. The Mechanical Design Process. Fourth edition ed. New York, NY 10020: McGraw-Hill; 2010.

[17] Herstatt C, Stockstrom C, Verworn B, Nagahira A. Fuzzy front end practices in innovating Japanese companies. IJITM. 2006;3(01):43-60.

[18] Quinn JB. Managing innovation: controlled chaos. Harvard Bus Rev 1985;63(3):73-84.

[19] Veryzer RW. Discontinuous innovation and the new product development process. J Prod Innovat Manag 1998;15(4):304-21.

[20] Srinivasan V, Lovejoy WS, Beach D. Integrated product design for marketability and manufacturing. J MARKETING RES 1997:154-63.

[21] Koen P, Ajamian G, Burkart R, Clamen A, Davidson J, D'Amore R, et al. Providing clarity and a common language to the Fuzzy Front End. Res Technol Manage 2001 Mar-Apr;44(2):46-55.

[22] Yin RK. Case study research: Design and methods. Thousand Oaks, California 91320: Sage Publications, Incorporated; 2008.

[23] Elverum CW, Welo T, Steinert M. Early concept development in the automotive industry: challenges related to the creation and implementation of viable solutions. R&D Manage Conference; 2013 June 26-28; Manchester, United Kingdom.

[24] Backman M, Borjesson S, Setterberg S. Working with concepts in the fuzzy front end: exploring the context for innovation for different types of concepts at Volvo Cars. R&D Manage 2007 Jan;37(1):17-28.

[25] Hall RR. Prototyping for usability of new technology. Int J Hum-Compu St 2001;55(4):485-501.

[26] Ulrich TK, Eppinger DS. Product Design and Development. 5th ed: McGraw-Hill; 2012.

[27] Kim J, Wilemon D. Focusing the fuzzy front-end in new product development. R&D Manage 2002 Sep;32(4):269-79.