4.4 Interstate Collaborations
Studies have shown that teams produce more creative and impactful research than single authors do.35 From 2004–2013, single-authored publications in the U.S. achieved a field-weighted citation impact of 0.80, below the world average field-weighted citation impact of 1.00 and well below the U.S. overall average of 1.49. The percentage of the United States’ total research publications that were single-authored declined from 17.5 percent in 2004 to 12.4 percent in 2013, consistent with the global trend.36
This section focuses on a particular type of team collaborations—those that span multiple U.S. states—
which measures interstate research collaborations through co-authorship. For example, when a publication has one author from the University of Kentucky and another author from the University of Kansas, this report defines that to be a collaboration between the states of Kentucky and Kansas.
States with large research outputs tend to have more collaborations than other states, which is addressed by using a normalized measure of collaboration—called Salton’s measure of collaboration strength— that takes into account the size of each state’s total research output.37 The values of Salton’s measure can vary between 0 (where there are no co-authored publication between a given pair of states) and 1 (in which every publication of each state was a collaboration with the other state). In practice, the range typically seen at state level is between 0.000 and 0.080 for most pairings of significant size).38
Even when the size of states’ research outputs is taken into account, the most prolific pairs of states tended to be those with the highest research outputs overall. For example:

Table 4.1—Research Collaboration Partnerships between U.S. States, 2004–2013. Pairings are sorted by Salton’s measure of collaboration strength. Source: Scopus® 

Case Study: Nevada’s Interstate Research Collaborations

Figure 4.6—Research Collaboration Partnership between Nevada and Immediate State Neighbors. Source: Scopus® Note: Thickness of arcs corresponds to Salton’s measure of collaboration strength. Labels correspond to number of collaborations between Nevada and that state between 2004–2013.

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