政大機構典藏-National Chengchi University Institutional Repository(NCCUR):Item 140.119/48933
English  |  正體中文  |  简体中文  |  Post-Print筆數 : 27 |  全文筆數/總筆數 : 93244/123616 (75%)
造訪人次 : 27854383      線上人數 : 490
RC Version 6.0 © Powered By DSPACE, MIT. Enhanced by NTU Library IR team.
搜尋範圍 查詢小技巧:
  • 您可在西文檢索詞彙前後加上"雙引號",以獲取較精準的檢索結果
  • 若欲以作者姓名搜尋,建議至進階搜尋限定作者欄位,可獲得較完整資料
  • 進階搜尋
    請使用永久網址來引用或連結此文件: http://nccur.lib.nccu.edu.tw/handle/140.119/48933

    題名: 山寨創新模式之探討
    An investigation into the shanzhai innovation model
    作者: 高鴻翔
    貢獻者: 李仁芳
    關鍵詞: 創新
    日期: 2009
    上傳時間: 2010-12-08 01:53:29 (UTC+8)
    摘要: 資源與能力薄弱的新興國小型後進廠商,為何能超越歐美先進廠商搶佔新興市場?在此研究動機之下,本研究透過質性研究之紮根理論,利用次級資料、廠商訪談、通路觀察等方法,收集產業體系、創新平台、經營環境等背景因素,以及產品/廠商定義、競爭優勢、創新特性、廠商樣貌等資料,解析中國手機產業之山寨廠商創新模式,並經由汽車、筆記型電腦等跨產業應用個案之對照,藉以延伸從創新獲利(Profit from Innovation)、顛覆式創新(Disruptive Innovation)、後進廠商(Late Entrant)的理論架構,作為新興國家後進廠商發展創新事業模式的思考架構。

    Why the overall market shares of international companies in the Chinese market dropped from over 90% in 2000 to under 50% due to competitions from local brands and Shanzhai phones? Why Nokia, the company that dominates the Chinese and Indian mobile phone markets has a 60% market share in India, but less than 30% in China? The key to this difference lies in differences in degree of industrial system development, resulting in varied market competition conditions.
    In recent years, through the “simplicity/reduction/ frugality” Shanzhai model, small local companies have dominated the local market and replaced the local brands under active government promotion. The products have been exported to India, Southeast Asia, and other emerging markets, making MediaTek Inc. one of the world’s top 5 IC design companies as well as the rapid development of the “Shanzhai model” in other sectors. Many firms now attach great importance to the challenges and underlying business opportunities ahead. The Government in Mainland China even changed from initially rejecting the idea into positioning it as the “primary innovation” for underdeveloped countries.
    So, is “Shanzhai Model” a speculative bubble from the underground economy of the emerging markets or is it a unique and innovative business model or a competitor that deserves firms’ attention? Most people raise questions over its sustainable business development from perspectives of copying, illegality, and hit-and-run. However, for more than four years since its development (specifically since the emergence of Shanzhai phones in the Chinese mobile phone market in 2005), there has been considerable increase in growth and market share (i.e., over 30% market share in 2008). In view of some firms’ successful transformation into the leading local brands (such as Tianyu, Beijing), interdisciplinary development (T.V., notebook computer, automobile, T.V. programs), etc., by analyzing the innovations in development strategies will perhaps help solve the puzzle of their competitiveness.
    The Shanzhai model is defined as “The flexible use of capabilities and resources in and outside the organization not bound by organizational boundaries through industrial vertical alliance of new firms in emerging countries. In consideration to Price-to-Performance Ratio, in order to reduce costs and enhance the target of customer value perception, accept or reject product features freely, quality (lifespan, safety), intellectual property, brand, taxes, and breakthroughs in consumer income, region, and time. Moreover, through consumer information feedback, products are quickly adjusted to meet consumer needs, surpass advanced American and European firms, gain entry in the “good-enough segment” market, and in turn create revenues.
    In view of the practical implications, this study is expected to shape two dimensions including the capability of the “Price-to-Performance Ratio” in reducing costs and the speed of market response through interviews with middle stream and downstream mobile phone, automobile, and notebook PC firms in the Greater China Region in order to analyze the strategic alliance underneath Shanzhai firms in Mainland China and the possibility of long-term survival.
    Theoretically, the literature reviews cover firms with abundant resources and capabilities in process innovation and complementary assets according to Christensen and Rosenbloom. Based on the value network perspective, although first movers with inferior technology defeat the leading firms that chose the existing major clients over the opportunity to invest in the latest technology and the late-entrants succeeded at the expense of the established firms. Therefore, the focus lies in resolving the established firms’ management agendas in response to disrupted innovation while research cases and the late-entrants’ framework of thought are relatively scarce.
    Therefore, the innovative business model for late-entrants of emerging countries shall serve as basis in exploring the late-entrants with scarce resources and capabilities and how they surpass the first movers in the emerging market. The vertical strategic alliance framework will be elaborated. The key to the first movers’ success is further discussed as basis for the late-entrants’ framework of thought in the innovative business model.

    The existing literature generally attributes the success of attackers to the failure of first movers. First movers’ failure to cultivate process capabilities (Abernathy & Utterback, 1978, 2004), inability to secure technological appropriability, lack of complementary assets required for commercialization (Teece, 1986, 2006), restrictions of sunk costs (Richard A. D‘Aveni, 1994), or limitations in investment decision making due to considerations of the existing mainstream customers (Christensen & Rosenbloom, 1995) gave the attackers the chance to flourish. Although we know the reasons that contribute to the first movers’ failure, we are unable to find out the secret to the innovative attackers’ success. Just as Jacobides, Knudsen and Augier (2006) mentioned, in order for firms to derive profits, other than taking appropriability of value into consideration, the creation of value is also worth noting. Also, Teece et al. (1997) believe that in terms of privately owned resource creation, discovering new opportunities and efficient and effective organization to seize the opportunities are of fundamental importance rather than engaging in strategies that cause competitors to lose balance or increase costs, or barricading newcomers. In order for attackers to surpass the first movers, it takes more than beating the opponent that has made mistakes in the competition; it is the innovative business model that has created higher values for the customers. Therefore, in order to find answers to the outcomes, we must first review what mistakes the first mover has made and analyze what the attacker has done right.
    In addition, Teece’s PFI (1986, 2006), Christensen’s disruptive innovation (1995, 1997, 2003, 2004), and the victory of attackers’ in emerging countries and related literature mostly focus on the organizational level rather than analysis on industrial level. Most of them interpret the success of the attackers from the internal organization perspectives. And analysis on attackers’ good use of the industrial system despite their lack of resources and capabilities is not much covered.

    Although the Shanzhai model has been under development for a very long time, the real concern for all fields originated from China’s mobile phone industry.Shanzhai firms of mobile phones, automobiles, and notebook computers in China have been selected as the study objects.
    The main purpose of this study is to explore the late-entrants in emerging countries that are seemingly counterfeiting and lack innovation by analyzing the development strategies of Shanzhai firms in mobile phone, automobile, and notebook computer sectors in Mainland China and the reason why they grow year after year. Since analysis on the development of the underground economies of developing countries is involved, in the absence of credible information, the study has established its research validity through three different data. First of all, secondary data, media reports, and related reports of companies and research units were collected to gain a preliminary understanding of the industrial environment, market development status, and strategies and actions of firms. Secondly, in order to overcome factors such as Shanzhai firms’ covert action, concealed information, and differed strategic types, and avoidance of information from single source that result in “taking a part for the whole” and bias, the researcher scheduled interviews in Beijing, Shanghai, and Shenzhen China for a period of one week to half a month in Auguest 2006, June 2007, September 2008, November 2008, September 2009, and October 2009 and non-structural interviews by telephone interview. Presidents GMs, R and D vice presidents, business vice presidents, and marketing managers of 55 enterprises and units including 94 component manufacturers, design centers, assembly manufacturers, retailers, think tanks, and private equity firms were interviewed (136 interviews).
    In terms of analysis, this study focuses on industry in order to enhance the practical application value.In data analysis, we used the grounded theory techniques, and through three steps of analysis focusing on market competition dynamics, relative competitive advantage and innovative model respectively, we gradually uncovered the phenomenon and reasons why Shanzhai firms can build a strong presence in the emerging market.

    In view of Shanzhai firms’ innovative model of mobile phones, notebook computers and automobiles in China, three keys are summarized including: value activity restructuring, vertical alliance and market testing.
    (1)Value Activity Restructuring
    Due to failure to smoothly enter the global production network dominated by U.S. and European first-movers, the Shanzhai firms constructed a unique value network at border areas of industries through value-activity restructuring by using the industries’ existing infrastructure, gathering other industrial minority firms and expanding operation scope to make up for partners’ lack of capability.
    (2)Vertical Alliance
    Contrary to the global production networks under the dominance of U.S. and European firms., Shanzhai firms survived by means of their core abilities and collaborated to build a common innovation platform to make up for their own lack of resources and capacity.
    (3)Market Testing
    To conduct market testing of their highly diverse, high performance-price products to respond quickly to market changes, Shanzhai firms started in dynamic and ambiguous niche markets which first movers typically ignored to gradually move to the mainstream market.

    In exploring the process and the influencing factors of the dynamic reorganization of Shanzhai firms’ value activities, this study may compensate for the lack of business model in Teece’s PFI structure on the relatively static description of complementary assets.
    Moving the focus from technology to business model, this study, besides supporting the Christensen’s value network and disruptive innovation viewpoint, replaces the traditional and rigid market prediction model or reliance on business leaders’ wisdom by exploring the emerging dynamic markets by launching a range of high performance-price products to test the market and respond to market changes. Meanwhile, the study of the innovative business model of attackers in emerging countries adds another perspective to first movers’ failure stressed by Teece and Christensen.
    According to research by Bhattacharya & Michael (2008), Zeng & Williamson (2008), and Kim (1997) that focused on scientific and technological imitation, innovation strategies, and innovative types of less advanced countries’ late-entrants, this study suggests that manufacturers with weak resources and capabilities utilize the existing industrial system and build an innovation platform of the unique value proposition to create competitiveness through integration.
    It is found in this study that due to diverse industry features, the same innovation model may face different challenges in cross-industry applications. As most existing research work focuses discussions on the firm- or national level, this study suggests researchers ponder on the industry level related research.
    第一章 緒論 1
    第一節 研究背景與動機 1
    第二節 研究問題與目的 3
    第二章 文獻探討 5
    第一節 從創新獲利 7
    第二節 顛覆式創新 11
    第三節 新興國家後進廠商發展策略 19
    第四節 文獻總結 21
    第三章 研究方法 23
    第一節 方法論與研究歷程 23
    第二節 資料收集範圍與方法 26
    第三節 資料分析方法 34
    第四章 中國大陸山寨手機廠商之創新策略 37
    第一節 山寨機之產品與廠商定義 37
    第二節 山寨機之競爭優勢 43
    第三節 山寨機廠商形塑競爭優勢之創新策略 47
    第四節 山寨機廠商不同時空下的面貌剖析 60
    第五章 山寨手機之制度影響因素探索 73
    第一節 降低進入障礙之研發平台誕生 74
    第二節 產業政策形塑下之中國大陸手機產業體系 84
    第三節 山寨產品的經營環境 92
    第六章 山寨模式的跨產業應用 95
    第一節 中國大陸小筆電個案 95
    第二節 中國大陸汽車廠商的山寨模式 102
    第三節 中國大陸平面電視廠商的山寨模式 107
    第七章 研究結論與意涵 109
    第一節 結論 109
    第二節 討論 115
    第三節 研究意涵 123
    參考文獻 129
    參考文獻: 李仁芳,1992,管理心靈,台北:商略出版社
    李仁芳、高鴻翔, 2008,掌握價值活動重組契機-後進廠商的邊陲進入策略,2008年中華民國科技管理學會年會暨論文研討會
    李仁芳、高鴻翔, 2009,快速試驗、精簡多餘、靈活整合的山寨創新學----以中國大陸山寨手機廠商為例 , 2009年中華民國科技管理學會年會暨論文研討會
    李仁芳、高鴻翔, 2009,價值活動重組、垂直聯盟、市場試驗----山寨創新模式之探討, 2009年『整合兩岸資源、開創台灣全球商機』研討會論文集,管理科學學會
    李仁芳、高鴻翔, 2010,山寨創新模式與智財權議題之探討,第八屆海峽兩岸智慧財產權學術交流研討會,政治大學智慧財產研究所、政治大學科技管理研究所、磐安智慧財產教育基金會、台灣技術經理人協會
    李仁芳、高鴻翔, 2010,快速試驗、精簡多餘、靈活整合的山寨創新學----以中國大陸山寨手機廠商為例 , 中山管理評論(2010.7.已接受)
    Abernathy, W. J. and Utterback, J.H., 1978. Patterns of Innovation in Technology, Technology Review, Vol.80 (July):pp.40-47.
    Abernathy, W. J. and Utterback, J. H., 2004. Patterns of Industrial Innovation, Strategic Management of Technology and Innovation, McGraw-Hill Press, pp.202-208.
    Amit, R. and Zott, C., 2001. Value-creation in e-Business, Strategic Management Journal 22, pp.493-520.
    Anderson, C., 2006. The Long Tail: Why the Future of Business is Selling Less of More, Wired Magazine
    Anthony, S. D., and Christensen, C. M., 2003. Performance, Convenience, Price: What's Your Brand About?, Strategy and Innovation 1, no. 4 (November/December).
    Anthony, S.D., Johnson, M.W., Sinfield, J.V., and Altman, E.J., 2008. The Innovator’s Guide to Growth: Putting Disruptive Innovation to Work, Perseus Distribution Services
    Baldwin, C. Y. and Clark, K. B., 1997, Managing In An Age of Modularity, Harvard Business Review, Vol. 75(5), pp.84-93.
    Bhattacharya, A.K. and Michael, D.C., 2008. How Local Companies Keep Multinationals at Bay, Harvard Business Review, March: pp.85–95.
    Bennett, D., 2009. The Black Market in China Lightens up, ANZMAC
    Bigus, O. E., Hadden, S. C., and Glaser, B. C., 1982.Basic Social Process, in R. B. Smith and P. K. Manning(eds.), Qualitative Methods: Handbook of Social Science Method (Ⅱ). Cambridge, MA: Ballinger.
    Blumer, H., 1969. Symbolic interaction. Englewood Cliffs, NJ: Prentice-Hall
    Bower, J. L. and Christensen, C. M., 1995. Disruptive Technologies: Catching the Wave, Harvard Business Review, 73, no. 1 (January-February ): pp.43-53.
    Bryce, D.J. and Dyer, J.H., 2007. Strategies to Crack Well-Guarded Markets, Harvard Business Review, no. 5
    Bryman, N., 1998. Quantity and Quality in Social Research, London:Unwin Hyman.
    Chandy, R. and Tellis, G. J., 1998. Organizing for Radical Product Innovation , Journal of Marketing Research, 35 (November),pp.474-487.
    Chesbrough and Rosenbloom , 2000.The role of business model of capturing value from innovation”, Harvard Business School Press.
    Chiasson, M. and Davidson, E.J., 2005. Taking Industry Seriously in Information Systems Research, MIS Quarterly, 29 (4), pp.591-605
    Christensen, C.M., 1997. The Innovator‘s Dilemma: When New Technologies Cause Great Firms to Fail, Boston, Mass.: Harvard Business School Press
    Christensen, C.M., Anthony, S.D., and Roth, E.A., 2004. Seeing What’s Next: Using the Theories of Innovation to Predict Industry Change, Boston: Harvard Business School
    Christensen, C. M. and Bower, J.L., 1996. Customer Power, Strategic Investment, and the Failure of Leading Firms, Strategic Management Journal, 17, no. 3 (March): pp.197-218.
    Christensen, C.M., Craig, T., and Hart, S., 2001. The Great Disruption, Foreign Affairs 80, no.2
    Christensen, C.M. and Overdorf, M., 2000. Meeting the Challenge of Disruptive Change, Harvard Business Review ,78, no. 2:pp. 66-76.
    Christensen, C.M. and Raynor M.E., 2003. The Innovator‘s Solution: Creating and Sustaining Successful Growth, Boston: Harvard Business School Press
    Christensen C.M., Raynor, M.E., and Anthony, S.D., 2003. Six Keys to Building New Markets by Unleashing Disruptive Innovation, HBSWK
    Christensen, C. M. and Rosenbloom, R.S., 1995. Explaining the Attacker's Advantage: Technological Paradigms, Organizational Dynamics, and the Value Network, Research Policy, 24, no.2 (March).
    Cooper, A.C. and Schendel, D., 1976. Strategic Responses to Technological Threats, Business Horizons, Vol. 19, pp. 61-69.
    Crowston, K., and Myers, M. D. 2004. Information Technology and the Transformation of Industries: Three Research Perspectives, Journal of Strategic Information Systems (13), 2004, pp. 5-28.
    Denzin, N. K. and Lincoln, Y. S., 2000. Handbook of Qualitative Research, 2nd edition, Thousand Oaks, CA:Sage.
    Dewey, J., 1934. Art as experence. New York: Minton, Balch.
    Dorothy, L.B., 1995. Wellspring of Knowledge: Building and Sustaining the Sources of Innovation, Harvard Business School Press
    Eisenhardt, K.M. and Martin, J.A., 2000. Dynamic Capabilities: What are they?, Strategic Management Journal, 21:pp.1105-1121.
    Eisenmann, T. R., 2002. Internet Business Models, McGraw-Hill.
    Foster, R., 1986. Innovation: The Attacker's Advantage, New York
    Gadiesh, O., Leung, P., and Vestring, T., 2007. The Battle for China’s Good-Enough Market, Harvard Business Review, no.9.
    Ghoshal, S. and Moran, P., 1996. Bad for Practice: A Critique of the Transaction Cost Theory, Academy of Management Review, vol.21, no. 1, (1996), pp.13-47.
    Glaser, B. and Strauss, A. L., 1967. The Discovery of Grounded Theory. NY:Aldine.
    Habermas, J., 1968. Knowledge and Human Interests. Boston: Beacon.
    Hamel, G., 2000. Leading the Revolution, Harvard Business School Press
    Hamel, G. and Prahalad, C. K., 1994. Competing for the future : breakthrough strategies for seizing control of your industry and creating the markets of tomorrow, Harvard Business School Press
    Hammersley, M., 1989. The Dilemma of Qualitative Method: Herbert Blumer and the Chicago Tradition. London and New York: Routledge.
    Helfat, C.E. and Lieberman, M.B. 2002. The birth of capabilities: market entry and the importance of pre-history, Industrial and Corporate Change ,Vol 11 (4), pp.725–760.
    Henderson, R. M. and Clark, K. B., 1990. Architectural Innovation: The Reconfiguration of existing Product Technologies and the Failure of Established Firms, Administrative Science Quarterly,Vol.35: pp.9-30.
    Hill, C., 1990. Cooperation, opportunism, and the invisible hand: implications for transactioncost theory. Academy Management Review, 15(3): 500-513.
    Hobday, M., 1995. Innovation in East Asia: the Challenge to Japan. Edward Elgar
    Jacobides, M.G., Knudsen, T.,and Augier, M., 2006. Benefiting from Innovation: Value creation, value appropriation and the role of industry architectures, Research Policy, Vol.35 (3) : pp.1200–1221
    Johnson, M.W., Christensen, C.M., and Kagermann, H., 2008. Reinventing Your Business Model, Harvard Business Review, 86, no. 12
    Kao, H. H. and Lee, J. F., 2009. An Unintended Result of a Well-Intentioned Policy – a Deep-Dive into China’s Mobile Phone Industry Policy, DURID Summer Conference 2009(Jun.), Copenhagen
    Kao, H. H. and Lee, J. F., 2010.The Shanzhai Way of Innovation – Testing, Reduction, and Integration, IAMOT Conference 2010(Mar.), Cairo
    Kao, H. H. and Lee, J. F., 2010. The Application of Shanzhai Innovation Model in China : The Examples of Mobile Phone, Notebook Computer, and Automobile, DRUID Conference 2010(Jun.), London
    Kao, H. H. and Lee, J. F., 2010. An Investigation into the Key Elements of the Chinese Shanzhai Model – Alternative Path to Growth, Cross-Specialization Partnership, and Opportunistic Niche Infiltration, PICMET Conference 2010(Jul.), Phuket
    Kao, H. H. and Lee, J. F., 2010. Disruptive Innovation of Shanzhai Firms in China, AOM Conference 2010(Aug.), Montreal (Accepted)
    Kim, L., 1997. Imitation to innovation the dynamics of Korea's technological learning,HBS press
    Markides, C. C. and Geroski, P. A. , 2004. Fast Second: How Smart Companies Bypass Radical Innovation to Enter and Dominate New Markets, John Wiley & Sons, Inc.
    Mintzberg, H., 1987. Crafting Strategy, Harward Business Review, pp. 66-75.
    Mitchell,W., 1989. Whether and when? Probability and timing of incumbents’ entry into emerging industrial subfields, Strategic Management Journal,18,pp.733-744
    Moore, G. A., 1991. Crossing the chasm : marketing and selling high-tech products to mainstream customers
    Pettigrew A. M., 1990. Longitudinal Field Research on Change: Theory and Practice, Organization Science, Vol. 1, No.3, (Special Issue), pp.267-292
    Pisano, G., 2006. Profiting from innovation and the intellectual property revolution, Research Policy, Vol. 35 (3),pp.1122–1130
    Pisano, G. and Teece, D., 2007. How to Capture Value from Innovation: Sharping Intellectual Prpperty and Industry Architecture, California Management Review, Vol. 50(1),pp.278-296
    Porter, M., 1993. The Technological Dimension of Competitive Strategy, Research on Technological Innovation, Management, Policy, vol.1, JAI Press, Inc
    Prahalad, C. K., 2005. The Fortune at the Bottom of the Pyramid: Eradicating Poverty Through Profits ,Pearson Education, Inc, New Jersey
    Richard A. D‘Aveni, 1994. Hypercompetition: Managing th Dynamics of Strategic Maneuvering, The Free Press.
    Ritchie, J. and Lewis, J., 2003. Qualitative Research Practice: A Guide for Science Students and Researchers, Sage Publications Ltd.
    Roussel, P., Saad, K. and Erickson, T., 1991. Third Generation R&D, Briefing Paper 1 Technology, Maturation, and Competitive Impact
    Roussel, P., Saad, K. and Erickson, T., 1991. Third Generation R&D, Briefing Paper 2 Technological Competitive Position
    Schnaars, S. P., 1994. Managing Immitation Strategies, New York: Free Press.
    Schumpeter, J.A., 1934. Theory of Economic Development. Cambridge: Harvard University Press.
    Strauss, A., 1987. Qualitative Analysis for social Scientists. Cambridge: Cambridge University Press
    Strauss, A., Bucher, R., Ehrlich, D., Schatzman, L., and Sabshin, M., 1964. Psychiatric ideologies and institutions. Glencoe, IL:Free Press
    Strauss, A. and Corbin, J., 1990. Basics of Qualitative Analysis Grounded Theory Procedures and Techniques. Newbury Park, CA:Sage.
    Teece, D., 1986. Profiting from technological innovation:Implications for integration, collaboration, licensing and public policy, Research Policy, Vol.15, pp.285-305
    Teece, D., 2006. Reflections on ‘Profiting from Innovation’ , Research Policy, Vol. 35 (3), pp.1131–1146
    Teece, D., 2007. Explicating Dynamic Capabilities: The Nature and Microfoundations of (Sustainable) Enterprise Performance, Strategic Management Journal, Vol.28, pp.1319–1350
    Teece, D., Pisano, G., and Shuen, A., 1997. Dynamic Capabilities and Strategic Management, Strategic Management Journal, Vol. 18(7): pp.509-533.
    Tellis, G. J. and Golder, P. N., 2002. Will and Vision: How Latecomers Grow to Dominate Markets, New York: McGraw-Hill Companies, Inc.
    Tripsas, M., 1997. Unraveling the process of creative destruction: complementary incumbent survival in the typesetter industry, Strategic Management Journal, Vol.18, pp.119–142
    Vernon, R., 1979. The product cycle hypothesis in a new international environment, Oxford Bulletin of Economics and Statistics, pp.255-267
    Wells, L. T., 1972. The product life cycle and international trade ,Boston: Graduate school of business administration, Harvard University
    Yin, R. K., 1989. Case Study Research: Design and Methods. Sage, Newbury Park, CA.
    Zeng, M. and Williamson, P.J., 2008. Dragons at your door: How Chinese cost innovation is disrupting global competition, Beijing: China Machine Press
    描述: 博士
    資料來源: http://thesis.lib.nccu.edu.tw/record/#G0095359501
    資料類型: thesis
    顯示於類別:[科技管理研究所] 學位論文


    檔案 大小格式瀏覽次數


    社群 sharing

    DSpace Software Copyright © 2002-2004  MIT &  Hewlett-Packard  /   Enhanced by   NTU Library IR team Copyright ©   - 回饋