A description of the terminology and methodology used in this supplement, and a guide to the functionality available online at natureindex.com.
The Nature Index is a database of author affiliations and institutional relationships, used to track contributions to articles published in a small group of highly selective journals that have been chosen by an independent group of working scientists.
Data in the Nature Index are updated monthly, with the most recent 12 months of data available under a Creative Commons licence at natureindex.com. The database is compiled by Nature Publishing Group (NPG) in collaboration with sister company Digital Science.
Nature index metrics
There are three measures provided by the Nature Index to track affiliation data. The simplest is the article count (AC). A country or institution is given an AC of 1 for each article that has at least one author from that country or institution. This is the case whether an article has one or a hundred authors, and it means that the same article can contribute to the AC of multiple countries or institutions.
To get a better sense of a country or institution's contribution to an article, and to remove the issue of double-counting of articles, the Nature Index uses the fractional count (FC). FC takes into account the relative contribution of each author to an article. The total FC available per paper is 1, and this is shared between all authors under the assumption that each contributed equally. For instance, a paper with 10 authors means that each author receives an FC of 0.1. For authors with joint affiliations, the individual FC is then split equally between each affiliation.
The third measure is the weighted fractional count (WFC), which applies a weighting to the FC in order to adjust for the over-representation of papers from astronomy and astrophysics. The four journals in these disciplines publish about 50% of all papers in international journals in this field — approximately five-times the equivalent figures for other fields. Therefore, although the data for astronomy and astrophysics are compiled in exactly the same way as for all other disciplines, articles from these journals are assigned one-fifth the weight of other articles (i.e. the FC is multiplied by 0.2 to derive the WFC).
The total FC or WFC for an institution is derived by summing the FC or WFC for individual authors. The process is similar for countries, although complicated by the fact that some institutions have overseas labs that will be counted towards the host country totals. What's more, there is great variability in the way authors present their affiliations. Every effort is made to count affiliations consistently, making reasonable assumptions. For more information on how the affiliation information is processed, please see the frequently asked questions at natureindex.com.
Nature Index 2014 Global is based on a snapshot of data from natureindex.com, covering articles published between 1 January and 31 December, 2013.
Most analyses within the Nature Index 2014 Global supplement use the WFC as the primary metric, as it provides a more even basis for comparison across multiple disciplines, and in determining the relative contribution of each country/institution.
Additional layers of information concerning funding levels, numbers of researchers, size of population and so on, are taken from publicly available sources. In several places, we use altmetrics as a supporting data source. Altmetrics is an alternative way to measure the impact of a paper by tracking different online sources (newspaper stories, tweets, blog posts, comments) that mention the paper. The altmetric score for an article gives an idea of the attention that it has received. Our data are from altmetric.com, provided by the start-up company Altmetric — which is supported by Digital Science. To see more about how this score is calculated, please visit support.altmetric.com.