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发信人: kuangshui ((▄︻┻┳═一)), 信区: Postgraduate
标 题: How to Build an Economic Model in Spare Time 4
发信站: 荔园晨风BBS站 (Sat Mar 25 23:06:09 2006), 站内
-4. Building your model
So let's skip the literature part for now and try to get to the modeling.
Lucky for you, all economics models look pretty much the same. There
are some economic agents. They make choices in order to advance their
objectives. The choices have to satisfy various constraints so there's
something that adjusts to make all these choices consistent. This basic
structure suggests a plan of attack: Who are the people making the choices?
What are the constraints they face? How do they interact? What adjusts
if the choices aren't mutually consistent?
Asking questions like this can help you to identify the pieces of a model.
Once you've got a pretty good idea of what the pieces look like, you can
move on to the next stage.
Most students think that the next stage is to prove a theorem or run a
regression. No! The next stage is to work an example. Take the simplest
example---one period, 2 goods, 2 people, linear utility---whatever it
takes to get to something simple enough to see what is going on.
Once you've got an example, work another one, then another one. See
what is common to your examples. Is there something interesting
happening here? When your examples have given you an inkling of
what is going on, then you can try to write down a model. The critical
advice here is KISS: keep it simple, stupid. Write down the simplest
possible model you can think of, and see if it still exhibits some
interesting behavior. If it does, then make it even simpler.
Several years ago I gave a seminar about some of my research. I started
out with a very simple example. One of the faculty in the audience
interrupted me to say that he had worked on something like this several
years ago, but his model was ``much more complex''. I replied ``My
model was complex when I started, too, but I just kept working on it till
it got simple!''
And that's what you should do: keep at it till it gets simple. The whole
point of a model is to give a simplified representation of reality. Einstein
once said ``Everything should be as simple as possible : : : but no
simpler.''
A model is supposed to reveal the essence of what is going on: your model
This takes a surprisingly long time---there are usually lots of false
starts, frustrating diversions, and general fumbling around. But keep at it!
If it were easy to do, it would have already been done.
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