I gave a talk at the Fletcher School today on my work on dyadic trade flows (slides).
In a nutshell, the talk argues that cartograms and dendrograms can give students and practitioners a better understanding of the patterns of trade among partner contries, both for teaching and for research. We have thousands of observations of dyadic relationships in panel datasets. Most often these datasets are presented as aggregates: total annual world trade, top exporters in world trade, top exporters, top exporters in an industry sector, top exporters to a political union (such as the EU), top exporters within a geographic area, etc. What these statistics ignore is the information in the dyadic trade flows: who trades with whom?
What I offer is a way to crunch down the total number of country dyads into manageable graphics that can appear on a single slide. We can look directly at the dyadic patterns of trade using hierarchic clustering (dendrograms). We can compare partner trade flows across countries and time periods using cartograms. The techniques are not new; what is new is the presentation of rich international trade datasets in relatively complete format that can be digested by inspection, rather than with complex and poorly understood statistical techniques. Complete annual sets of cartograms and dendrograms give scholars the power to explore the distribution of dyadic trade and discover hypotheses that are worth testing more carefully, either with quantitative or qualitative methods.
One of the reasons trade courses have focused so much on models, theorems, and policy of international trade is that it is hard to describe trade patterns in any meaningful and comparable terms. My slides suggest how to do exactly that: present changes to global trade patterns in a succinct, visual format that enables rich comparisons across time and space.