One of the most widely used proxies to assess the impact of scientific work are citations. Citations to scientific articles provide an indication of the extent to which the scientific work of a research unit/university/country has influence and impact on the world scientific community. The more citations a scientific oeuvre gets, the bigger its impact and relevance.
In this figure, the so-called 'Field-normalised Citation Impact Score' per scientific discipline is used as impact indicator. This indicator is considered as one of the most suitable measures for international comparisons. It is the ratio of the actual number of citations received per publication (excluding self-citations) published in a scientific sub-field to the ‘expected’ (average) number of citations received by all papers published worldwide in the same sub-field.
If the ratio is above 1.0, this means that the scientific oeuvre is cited more frequently than the world average. The denominator (average number of citations per sub-field) is a weighted average taking into account differences in impact between the journals related to the sub-field in question (thus high-impact journals are more heavily weighed than low-impact journals).
Compared to the US, the EU-25 demonstrates lower impact scores in 35 out of the 37 scientific disciplines [in two sub-fields of the Social Sciences the EU-25 shows a higher ('Information and Communication Sciences') or similar ('Social Geography and Demography') score]. The gap with the US is particularly striking (i.e. difference in citation impact >0.5) in disciplines such as ‘Chemistry’, ‘Computer Sciences’, ‘Material Sciences’ (in terms of number of publications the most important sub-field of the 'Engineering Sciences'), ‘Economics’, and ‘Statistical Probability and Analysis’.
Read more here (dated: 4 Apr 2007)