What is the effect of spatial proximity on research collaboration in a small country? A gravity model for co-authored publications

In this study we fit a gravity model for knowledge production, where the number of co-authored publications is explained by the size of the affiliated organisations and the physical distance between them. We analyse 2247 publications on drinking water and wastewater in the period 2006-2008 with at least one author affiliation in the Netherlands. At this small spatial level we find a robust and significant effect in the expected direction: the larger the distance between two organisations, the less publications they co-author together. We extend the model and show that organisations of the same type (academia, governmental bodies, etc.) also collaborate more