Measure the impact of scientific research of a country is of great interest to policy makers in order to define both the amount of its spending and its priorities. To study in a systematic way the scientific impact of nations, using simple and relevant indicators, data on the number of articles and citations produced by individual countries have been used in the past. Articles and citations are, in fact, an indirect measure of the output of the investment in research: the number of scientific articles is related to the activity carried out and the number of citations received by these articles measures popularity that one can consider correlated to the scientific quality. While, when referring to a single researcher these numbers should be treated with great caution, when considering the production of a whole country one can reasonably assume, thanks to the large numbers involved, that there is a proportionality between the total number of articles and citations and the global significance of the research.
Robert May was among the first to perform this type of analysis for the years 1981-1994; in particular compared the investments and the results of scientific research in various countries. Later, David King presented in 2004 a similar but more refined analysis, for the years 1993-2002. More recently, other studies, several national and international agencies, using a similar methodology, measured the productivity of scientific research of nations by normalising the number of scientific articles and citations received to the spending on research and university. In fact, when comparing very different countries (for example, the United States and Switzerland) it is necessary to take into account the fact that the global scientific production depends on the size of the country itself: for example, the number of researchers or total investment in research. As the number of researchers is not simply measurable (for example, in many countries there is a nontrivial problem in the census of not permanent researchers), it can be used as an indicator for comparing different countries, the spending on scientific research and development or the cost of higher education for research and development (the so-called HERD) that is surveyed by the OECD.
The political implications of this analysis are of two types. On the one hand we see the nations that are technology leaders, have the largest production of scientific articles and the highest number of citations. These countries also have the highest fraction of spending on research and development relative to GDP (almost 3%). On the other side, a comparative analysis of the impact of the different research areas can provide information about what is the most efficient way to implement your own search system: to specialise in certain areas of science or rather diversify as much as possible? In many countries is taking place in recent years, a worrying tendency to concentrate resources on a few centres of excellence and scientific projects, both decided in a top-down manner. To assess whether the latter is a policy that increases the efficiency of the system can be observed what happened in different countries over the past two decades, since when databases of publications and citations are available.
In a recent study, to measure the impact of research systems of the nations we have used a new method applied to the bibliometric data covering 238 countries, 27 scientific fields, which in turn are divided into 307 sub-fields. The ratio between the total number of citations and the expense HERD (expressed in dollars equivalent) for each country shows an almost linear behavior: this relationship simply implies that the production of scientific research depends linearly on the resources that a nation has invested in it. Nations above/below the line (for example, the United Kingdom, Israel, Canada, New Zealand, above; Japan, China, Mexico, Turkey, below) are more/less efficient in their scientific production compared to the average: a more refined analysis is therefore necessary to identify the reasons for these fluctuations. However at first approximation we can deduce that the scientific impact at the country level depends on the investment, with deviations from the mean rather contained in almost all countries in the world.
An analysis of the impact in the different scientific fields can answer the following problem: if nations tend to specialise or diversify their scientific research activities, and what is the most efficient in terms of scientific competitiveness. Since science is nothing more than one of the different results of a company, these problems are closely linked to that of the industrial output of the nations, for which some of the main economic theories classic prescribe specialisation, while recent studies show that nations are quite different and tend to produce all possible, that is to say, all this compatible with their capacity determined by the set of infrastructure, level technologist, educational system, efficiency of the State, etc.
To do this one can study the impact of extensive scientific research (total) and intensive (normalised to the resources invested) of countries at different research areas. To quantitatively assess the comparative advantage of diversification scientific one can use a new approach with which one can define a measure for both the competitiveness of scientific research of nations and for the complexity of the scientific areas. This approach has allowed us to identify the countries with both the research system more productive, both scientific fields that represent the best indicators of the level of development of the national system of scientific research. The conclusion is that, as is the case for industrial production, the nations most successful technology does not specialise in a few specific scientific domains but rather, diversify as much as possible their search system. Diversification is the key element for nations to achieve a successful and competitive research: this conclusion suggests that scientific excellence can be understood as a natural side effect of a complex, heterogeneous, diversified, and therefore healthy, system.