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Characterizing Informational Barriers To Entry In The Anti-Ulcer Drug Market

  • Matthew Shum

We empirically quantify and characterize informational barriers to entry into the anti-ulcer drug market by studying the diffusion process of the molecule Omeprazole in the first 30 months after it entered the market. Using a novel panel dataset tracking doctors' complete prescription histories, we specify and estimate a learning model in which doctors, initially uncertain about the quality differential between Omeprazole and the incumbent molecules, update their beliefs about this differential from first-hand experience after observing noisy signals from patients to whom they have prescribed the molecule. We find strong evidence that doctors' uncertainty about Omeprazole's quality is resolved by first-hand experience rather than through the pharmaceutical companies' marketing activities, so that learning through first-hand experience explains almost all of Omeprazole's diffusion path over our three-year sample period. This casts some doubt on previous researchers' findings, utilizing aggregate data, regarding the importance of marketing in securing market share for an entrant brand.

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File URL: http://www.economics.utoronto.ca/public/workingPapers/UT-ECIPA-MSHUM-98-03.ps
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Paper provided by University of Toronto, Department of Economics in its series Working Papers with number mshum-98-03.

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Length: 35 pages
Date of creation: 09 Oct 1998
Date of revision:
Handle: RePEc:tor:tecipa:mshum-98-03
Contact details of provider: Postal: 150 St. George Street, Toronto, Ontario
Phone: (416) 978-5283

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  1. Bagwell, Kyle, 1990. "Informational product differentiation as a barrier to entry," International Journal of Industrial Organization, Elsevier, vol. 8(2), pages 207-223, June.
  2. Schmalensee, Richard., 1980. "Product differentiation advantages of pioneering brands," Working papers 1140-80., Massachusetts Institute of Technology (MIT), Sloan School of Management.
  3. Levinsohn, James & Berry, Steven & Pakes, Ariel, 2004. "Differentiated Products Demand Systems from a Combination of Micro and Macro Data: The New Car Market," Scholarly Articles 3436404, Harvard University Department of Economics.
  4. Ernst R. Berndt & Robert S. Pindyck & Pierre Azoulay, 1999. "Network Effects and Diffusion in Pharmaceutical Markets: Antiulcer Drugs," NBER Working Papers 7024, National Bureau of Economic Research, Inc.
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