1. Introduction
Intangible assets are attracting major academic and policy interest in today‘s knowledge economies. Intangible assets, such as knowledge generated through investment in research and development (R&D), are assets that are not physical in nature yet deliver concrete economic benefits. Research has established that intangible assets account for a significant proportion of firms‘ value (Lev and Sougiannis 1996; Crépon et al. 1998; Webster 2000) and are an important driver of productivity growth (Adams 1990; Coe and Helpman 1995; Corrado et al. 2009). Although our understanding of intangible assets has progressed significantly, many open questions remain.
One such question is the speed at which these assets depreciate. This paper focuses on the private rate of depreciation of innovations, defined as the rate of decay of appropriable revenues from innovations (Pakes and Schankerman 1984). The depreciation rate of technological knowledge is a key economic parameter. It provides information about the speed of technological change and is essential for estimating the private returns to R&D investments (Pakes and Schankerman 1984; Esposti and Pierani 2003; Hall et al. 2010; Li and Hall 2016). In this regard, Hall (2005:342) argues that measurement of the depreciation of R&D assets is the ―central unsolved problem in the measurement of the returns to R&D‖. The ‗depreciation problem‘ arises from the difficulty in reconciling depreciation rates obtained using different methodologies (see also Griliches 1998).
