I took a class in causal modeling more than 10 years ago, and while I
thought I remembered the basics, since then all my work has been with
structural equation models, and I find I'm now a bit lost....
Let me explain what I'm trying. Basically, I'm trying to test the
hypothesis that high levels of press freedom tend to prevent violent
ethnic conflict, because ethnic groups can fight things out in the
media. Therefore, the main effect I'm looking for is an effect of
media freedom and ethnic violence, and my guess is that effect will
be a bit lagged, though I'm not sure of that, and it's also possible
that each variable affects the other. I have data at least back to
1990 in many, many countries for both of these, though I intend to do
the tests just in sub-Saharan Africa and post-Communist Europe.
Other endogenous variables that could affect the equation would be
democracy (the Freedom House political freedom score), unemployment,
and change in per-capita GDP. I'm working on figuring out exogenous
variables, but election years and possibly the presence of droughts
look good, and literacy rates (separately for men and women) might
also be useful.
My question is, how do I frame this. Basically, I should have time
series data for each variable for each of the countries in
question. Each country could therefore be analyzed individually, but
I'd ideally expect patterns within particular regions, if not across
regions. My memory vaguely recalls that I want to use SURE or some
kind of simultaneous equations analysis, but I've been looking
through the two relevant texts I have (Gujarati, Third Edition, and
Hamilton's Time Series Analysis), and come to the conclusion that I'm
a lot less smart than I thought I was, at least on this subject.
Could anyone give me a few pointers? And if those pointers included
tips on setting this up in GRETL, that would also help. One specific
question I have what do to with exogenous variables that don't vary
much over time. To wit, I'm suspect literacy rates play a role, but
since they don't change much over time, that roles should be seen
across countries rather than over time within countries (which is one
reason a multiple-country analysis would be useful).
Thanks,
Scott Orr