Studies in the field:

• Title: Accounting for Innovation and Measuring Innovativeness: An Illustrative Framework and an Application. Mairesse J.; Mohnen P. - The American Economic Review, 1 May 2002, vol. 92, no. 2, pp. 226-230(5). American Economic Association
  Available from Ingenta

• Title: Measuring innovative performance: is there an advantage in using multiple indicators?. Research Policy, Volume 32, Issue 8, September 2003, Pages 1365-1379, John Hagedoorn and Myriam Cloodt
  Available from doi:10.1016/S0048-7333(02)00137-3
  Abstract.
  The innovative performance of companies has been studied quite extensively and for a long period of time. However, the results of many studies have not yet led to a generally accepted indicator of innovative performance or a common set of indicators. So far the variety in terms of constructs, measurements, samples, industries and countries has been substantial. This paper studies the innovative performance of a large international sample of nearly 1200 companies in four high-tech industries, using a variety of indicators. These indicators range from R&D inputs, patent counts and patent citations to new product announcements. The study establishes that a composite construct based on these four indicators clearly catches a latent variable ‘innovative performance’. However, our findings also suggest that the statistical overlap between these indicators is that strong that future research might also consider using any of these indicators to measure the innovative performance of companies in high-tech industries.