Tuesday, April 10, 2012

Epidemics and Economies -- Network Theory, Constructal Theory, and Spontaneous Order Theory

Epidemiology studies the way diseases spread. Insofar as this spread can be understood through scale-free network theory and, thus, through constructal theory, there is really not much difference among understanding the spread of disease and the spread of ideas, whether technological, scientific, or artistic, and the spread of goods through an economy.

The flows of diseases, ideas, good, traffic, money, immigrants, etc. are all described using constructal theory, which underlies network theory. All give rise to the same network structures, with power law distributions. If you understand the structure of flows, you can understand much in the social sciences, psychology, the biological sciences, and even the physical sciences. Diseases, ideas, goods, etc. all do in fact flow like rivers. The fact that they are rivers layers on top of rivers does not mean the basic structures differ -- the only difference is in the complexity created from the overlaps and nested hierarchies. Yes, it matters which kinds of networks one is looking at, be it hierarchical or scale-free (all the ones mentioned above are scale-free), but many of the principles are the same.

Hierarchical networks are embedded in the scale-free networks, and have to be understood as such. If you mistake a scale-free network for a hierarchical network, you can make errors in judgement that can in fact kill people. If you understand the economy as being a hierarchical network rather than a scale-free network, you will make the mistake of thinking central planning (as one finds in firms) for an economy possible. Can one plan an epidemic? Of course not. But the same thing that will stop an epidemic will collapse an economy -- destruction of the most-connected nodes (in the case of an epidemic, targeting the most connected nodes/people with medicine to stop the spread). The person who understands spontaneous orders understands epidemics as well.

4 comments:

JWO said...

I am amazed at how new world have been integrated into the cuisines in very remote places. Things like potatoes, peppers and corn. Hot peppers in particular seemed have become major foods in very remote parts of Asia and Africa. They must travel very quickly.

Troy Camplin said...

Roots like potatoes and grains like corn are high energy foods, and thus are cheap foods, allowing the poor to receive more nutrition, so foods like those should not be surprising.

Hot peppers have a slightly different story. Spices have always been popular because they help to cover the taste of slightly spoiled food. Hot peppers are especially good at this. (This is why BBQ evolved in the American South and Southwest.) Further, not peppers have antibiotic properties, which means both the flavor and effect of slightly spoiled food can be fought with hot peppers. So, again, it should not be surprising they spread quickly, especially through places with warm climates.

Winton Bates said...

It is interesting that Henry Farrell and John Quiggin have recently used an epidemic model to discuss the return to influence of Keynesian deficit spending policies in the wake of the global financial crisis and the subsequent return of views more favourable to fiscal restraint (link available here.

I don't think they make the point that the return to popularity of deficit spending provides an example of a situation where the spread of the virus tends to be self correcting because it kills the host.

Troy Camplin said...

I think more and more epidemic models, precisely because they are network/constructal models (even when not explicitly acknowledged as such), are going to be used to describe the spread of idea, etc.

Of course, there are some specifics of epidemic models that seem unique to them -- such as weakened hosts giving rise to advantageous infections, differences between those diseases that kill the host vs. those that do not -- which are in fact quite applicable to a situation such as the rise of Keynesianism (and its fall when, once again, it fails).