High-level results from the Nature Index show three strong regions, but also reveal a more nuanced picture.
WFC: weighted fractional count (applies a weighting to correct imbalance)
FC: fractional count (apportions article count for each contributor)
AC: article count (number of papers)
Each region has a certain proportion of papers that are wholly authored by local researchers. The rest of the papers involve collaborators from other regions, but not always from those nearest to home. Note that each connecting arc assumes purely bilateral collaborations.
Frequency of collaboration
The ratio of article count (AC) to fractional count (FC) gives a measure of the region's propensity to collaborate. A higher number means more collaborators from outside the region per paper.
Dividing a country's weighted fractional count (WFC) by its gross domestic expenditure on research and development (GERD, per US$100,000, by purchasing power parity) gives a measure of its financial efficiency. So the larger the square, the higher the Nature Index output (as measured by WFC) per dollar invested. (Only countries with a WFC>10 and GERD data from 2008 or later are included. Source: United Nations Educational, Scientific and Cultural Organization (UNESCO).)
On a regional basis, North America has the highest WFC in three of the four subject areas. However, each region has a unique subject footprint.