Measuring firms’ imitation activity Ahmed Doha 1 , Mark Pagell 2 , Morgan Swink 3 and David Johnston 4 1 Assistant Professor of Supply Chain Management, Sprott School of Business, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6. ahmed.doha@carleton.ca 2 Chair in Global Leadership, Professor of Sustainable Supply Chain Management, School of Business, University College Dublin, UCD, Belfield, Dublin 4, Ireland. mark.pagell@ucd.ie 3 James L. and Eunice West Chair, Professor of Supply Chain Management, Neeley School of Business, Texas Christian University, 2900 Lubbock Ave, Fort Worth, Texas 76109, USA. m.swink@tcu.edu 4 Associate Professor of Operations Management and Information Systems, Schulich School of Business, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3. johnston@rogers.com Although imitation is more abundant and prevalent than innovation in firms’ product and process development activities, it has been understudied in research on innovation and R&D management. For example, a valid and reliable objective firm-level measure of the intensity of imitation activity is lacking in the extant literature. This measure is necessary to understand the antecedents and consequences of firms’ imitation activity, which has implications for R&D management. In this paper, we present novel methods that employ patent infringement litigations data to improve on the validity and reliability of measuring firms’ imitation activity. We validate our proposed measure by presenting a first model and test of R&D as a multiple-output production function with R&D expenditure as the primary input, and innovation and imitation as joint outputs. This is in contrast to current R&D models as a single-output production function of either innovation or imitation. This study uses a sample of 227 public firms from the computer, semiconductor, and pharma- ceutical industries in the United States during 1991–2010. 1. Introduction I nnovation and imitation are primary approaches that firms follow in product and process develop- ment. Zander and Kogut (1995) assert that ‘firms compete not only through the creation, replication, and transfer of their own knowledge, but also through their ability to imitate the product and process innova- tions of competitors’ (pp. 76). Imitation in particular is widely practiced (Minagawa et al., 2007) to the extent that some researchers (Schnaars, 1994; Levitt, 1966) consider it more abundant and prevalent than innovation in firms’ product and process development activities. The concepts of innovation and imitation are dis- tinct. Whereas innovation is a new design, product, or process technology developed by a firm (Katila and Ahuja, 2002), imitation is the unauthorized replication 1 V C 2016 RADMA and John Wiley & Sons Ltd