Authors:Michel Zitt, Suzy Ramanana-Rahary, and Elise Bassecoulard
The increasing use of bibliometric indicators in science policy calls for a reassessment of their robustness and limits. The
perimeter of journal inclusion within ISI databases will determine variations in the classic bibliometric indicators used
for international comparison, such as world shares of publications or relative impacts. We show in this article that when
this perimeter is adjusted using a natural criterion for inclusion of journals, the journal impact, the variation of the most
common country indicators (publication and citation shares; relative impacts) with the perimeter chosen depends on two phenomena.
The first one is a bibliometric regularity rooted in the main features of competition in the open space of science, that can
be modeled by bibliometric laws, the parameters of which are “coverage-independent” indicators. But this regularity is obscured
for many countries by a second phenomenon, the presence of a sub-population of journals that does not reflect the same international
openness, the nationally-oriented journals. As a result indicators based on standard SCI or SCISearch perimeters are jeopardized
to a certain extent by this sub-population which creates large irregularities. These irregularities often lead to an over-estimation
of share and an under-estimation of the impact, for countries with national editorial tradition, while the impact of a few
mainstream countries arguably benefits from the presence of this sub-population.
Authors:Michel Zitt, Suzy Ramanana-Rahary, and Elise Bassecoulard
Summary As citation practices strongly depend on fields, field normalisation is recognised as necessary for fair comparison of figures in bibliometrics and evaluation studies. However fields may be defined at various levels, from small research areas to broad academic disciplines, and thus normalisation values are expected to vary. The aim of this project was to test the stability of citation ratings of articles as the level of observation - hence the basis of normalisation - changes. A conventional classification of science based on ISI subject categories and their aggregates at various scales was used, namely at five levels: all science, large academic discipline, sub-discipline, speciality and journal. Among various normalisation methods, we selected a simple ranking method (quantiles), based on the citation score of the article in each particular aggregate (journal, speciality, etc.) it belonged to at each level. The study was conducted on articles in the full SCI range, for publication year 1998 with a four-year citation window. Stability is measured in three ways: overall comparison of article rankings; individual trajectory of articles; survival of the top-cited class across levels. Overall rank correlations on the observed empirical structure are benchmarked against two fictitious sets that keep the same embedded structure of articles but reassign citation scores either in a totally ordered or in a totally random distribution. These sets act respectively as a 'worst case' and 'best case' for the stability of citation ratings. The results show that: (a) the average citation rankings of articles substantially change with the level of observation (b) observation at the journal level is very particular, and the results differ greatly in all test circumstances from all the other levels of observation (c) the lack of cross-scale stability is confirmed when looking at the distribution of individual trajectories of articles across the levels; (d) when considering the top-cited fractions, a standard measure of excellence, it is found that the contents of the 'top-cited' set is completely dependent on the level of observation. The instability of impact measures should not be interpreted in terms of lack of robustness but rather as the co-existence of various perspectives each having their own form of legitimacy. A follow-up study will focus on the micro levels of observation and will be based on a structure built around bibliometric groupings rather than conventional groupings based on ISI subject categories.
Authors:Suzy Ramanana-Rahary, Michel Zitt, and Ronald Rousseau
Among classical bibliometric indicators, direct and relative impact measures for countries or other players in science are
appealing and standard. Yet, as shown in this article, they may exhibit undesirable statistical properties, or at least ones
that pose questions of interpretation in evaluation and benchmarking contexts. In this article, we address two such properties
namely sensitivity to the Yule-Simpson effect, and a problem related to convexity. The Yule-Simpson effect can occur for direct
impacts and, in a variant form, for relative impact, causing an apparent incoherence between field values and the aggregate
(all-fields) value. For relative impacts, it may result in a severe form of ‘out-range’ of aggregate values, where a player’s
relative impact shifts from ‘good’ to ‘bad’, or conversely. Out-range and lack of convexity in general are typical of relative
impact indicators. Using empirical data, we suggest that, for relative impact measures, ‘out-range’ due to lack of convexity
is not exceptional. The Yule-Simpson effect is less frequent, and especially occurs for small players with particular specialisation
Authors:Michel Zitt, Suzy Ramanana-Rahary, Elise Bassecoulard, and Françoise Laville
This article depicts some features of the geography of science and technology outputs in the EU, with a particular attention
to regional “co-location” of these two pillars of the “knowledge-based society”. Economists have, for a decade, paid great
attention to local “spillovers” stating that industrial firms often draw advantages from the presence of nearby academic centres.
The presence in the same areas of strong academic and technological resources is both a condition and a result of science-technology
interactions. Concentrating on publications and patents as proxies of the science and technology level in regions, we built
a typology of regions according to their commitment to the two knowledge-base activities and then analysed the co-locations
of science and technology from several points of view. A fine-grain lattice, mainly based on standard Nuts3 level, was used.
Co-location, at the EU level, is not a general rule. A strong potential for spillover/ interaction does exist in the top-class
regions which concentrate a high proportion of European S and T output. But for regions with a small/medium level of S&T activity,
a divergence of orientations appears between a science-oriented family and a technology-oriented family, indicating an imbalance
between local S and T resources. If we look at the S-oriented regions, whilst controlling for underlying factors, such as
population and regional economic product, a significant geographic linkage between T and S appears. This suggests a trajectory
of science-based technological development. A careful examination of S&T thematic alignments and specialisation is necessary
to develop the hypothesis that fostering academic resources could increase the technological power along a growth path.