These results may depend on the measure of innovation that is used. Indeed, Kuznets (1962) noted the problems with that the lack of appropriate innovation measures may create in economic research related to inventive activity. In recent years, considerable attempts have been made to measure technological innovation across countries. Wakelin (1997) classified different proxies for technological innovation used in the literature and pointed out that the main choice of technological innovation proxies was between using an input to the innovation process, such as Research and Development (R&D) expenditure or the number ofscientists and engineers employed in research departments, or an output, such as number of patents. In a more recent study, Keller (2004) pointed out that technological innovation is an intangible that is difficult to measure directly and that the three indirect approaches that can be used are the measurement of inputs (R&D), outputs (patents) and the effect of technological innovation (higher productivity).