Cherry-Picking Economic Models

by Lars P. Syll

How would you react if a renowned physicist, say, ​Richard Feynman, was telling you that sometimes force is proportional to acceleration and at other times it is proportional to acceleration squared?

I guess you would be unimpressed. But actually, what most mainstream economists do amounts to the same strange thing when it comes to theory development and model modification.

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In Dani Rodrik’s Economics Rules – just to take one illustrative example – the proliferation of economic models during the last twenty-thirty years is presented as a sign of great diversity and abundance of new ideas:

Rather than a single, specific model, economics encompasses a collection of models … Economics is in fact, a collection of diverse models …The possibilities of social life are too diverse to be squeezed into unique frameworks. But each economic model is like a partial map that illuminates a fragment of the terrain …

Different contexts … require different models … The correct answer to almost any question in economics is: It depends. Different models, each equally respectable, provide different answers.

In mainstream economic theory,​ preferences are standardly expressed in the form of a utility function. But although the expected utility theory has been known for a long time to be both theoretically and descriptively inadequate, mainstream economists all over the world gladly continue to use it, as though its deficiencies were unknown or unheard of.

What most mainstream economists try to do in face of the obvious theoretical and behavioural inadequacies of the expected utility theory, is to marginally mend it. But that cannot be the right attitude when facing scientific anomalies. When models are plainly wrong, you’d better replace them! Instead of mending the broken pieces it would be much better to concentrate on developing descriptively accurate models of choice under uncertainty.

Expected utility theory is seriously flawed since it does not take into consideration the basic fact that people’s choices are influenced by changes in their wealth. Where standard microeconomic theory assumes that preferences are stable over time, behavioural economists have forcefully again and again shown that preferences are not fixed, but vary with different reference points. How can a theory that doesn’t allow for people having different reference points from which they consider their options have a (typically unquestioned) axiomatic status within economic theory?

Much of what experimental and behavioural economics come up with, is really bad news for mainstream economic theory. It unequivocally shows that expected utility theory is nothing but transmogrifying truth.

But mainstream economists do not see this​ since they have the weird idea that economics is nothing but a smorgasbord of ‘thought experimental’ models. For every purpose you may have, there is always an appropriate model to pick.

But, really, there have​ to be some limits to the flexibility of a theory!

If you freely can substitute any part of the core and auxiliary sets of assumptions and still consider that you deal with the same theory, well, then it’s not a theory, but a chameleon.

The big problem with the mainstream cherry-picking view of models is of course that the theories and models presented get totally immunized against all critique. A sure way to get rid of all kinds of ‘anomalies,’ yes, but at a far too high price. So people do not behave optimizing? No problem, we have models that assume satisficing! So people do not maximize expected utility? No problem, we have models that assume … etc., etc …

A theory that accommodates for any observed phenomena whatsoever by creating a new special model for the occasion, and a fortiori having no chance of being tested severely and found wanting, is of little real value.

Caption graphic photo credit: From Cherry Picking, Team Mullen, flickr.

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