Although it has been suggested that innovation has significant consequences for a firm's economic performance, the past empirical findings are mixed, not always confirming this proposition. Extending previous research, this study demonstrates that the reason for previously conflicting results may be an incomplete understanding of the factors influencing the innovation-performance relationship. We argue that not all firms can reap rewards from innovation. Rather, we suggest that firms need to have a sufficient degree of internationalization, i.e. be active in many markets, to capture successfully the fruits of innovation. Initially, the study offers a theoretical framework that explains how and why a higher degree of internationalization, by affecting both innovative capacity and a number of appropriability factors, influences the effects of innovation. Then, utilizing firm-level data, the study empirically tests this proposition. The results confirm that internationalization enhances a firm's capacity to improve performance through innovation. However, they also show that firms are unable to benefit from innovation if their international activity is below a threshold level.

No abstract

This paper is primarily concerned with data envelopment analysis (DEA) of systems where negative outputs and negative inputs arise naturally. Examples of situations in which both negative inputs and negative outputs occur are given. More attention has been paid, in the literature, to the former type of problem. Most available DEA software does not solve this type of problem or copes with negative outputs and possibly negative inputs by assigning zero weights to them. A modified slacks-based measure (MSBM) model is presented, in which both negative outputs and negative inputs occur. The MSBM model overcomes the lack of translation invariance in the slacks-based measure model by drawing on the ideas from the range directional model (RDM). The MSBM model takes into account individual input and output slacks, which provides more precise evaluation of inefficient decision-making units (DMUs). It therefore, generally leads to lower efficiencies for inefficient DMUs than the RDM.

Tumour spheroids are common in vitro experimental models of avascular tumour growth. Compared with traditional two-dimensional culture, tumour spheroids more closely mimic the avascular tumour microenvironment where spatial differences in nutrient availability strongly influence growth. We show that spheroids initiated using significantly different numbers of cells grow to similar limiting sizes, suggesting that avascular tumours have a limiting structure; in agreement with untested predictions of classical mathematical models of tumour spheroids. We develop a novel mathematical and statistical framework to study the structure of tumour spheroids seeded from cells transduced with fluorescent cell cycle indicators, enabling us to discriminate between arrested and cycling cells and identify an arrested region. Our analysis shows that transient spheroid structure is independent of initial spheroid size, and the limiting structure can be independent of seeding density. Standard experimental protocols compare spheroid size as a function of time; however, our analysis suggests that comparing spheroid structure as a function of overall size produces results that are relatively insensitive to variability in spheroid size. Our experimental observations are made using two melanoma cell lines, but our modelling framework applies across a wide range of spheroid culture conditions and cell lines.