Integrate Gleditsch Expanded Trade and GDP data

[meflynn]

Integrate Gleditsch Expanded Trade and GDP data.

[svmiller]

Re: this. I think I want to do one better on the trade data and integrate the Anders et al. surplus GDP. Better coverage + CoW codes. It would really be no issue at all to add Gleditsch's stuff even as my orientation toward state system codes is more CoW than GW.

[svmiller]

FWIW, I added the Anders et al. version of the GDP data (along with their SDP measure). I don't know how eager I am to add the Gleditsch data for trade and GDP. The Anders et al. data have the GDP and population estimates that Gleditsch provides, helpfully standardized to both CoW and GW systems, which I think supplants what Gleditsch provides to 2011 for just the Gleditsch-Ward states.

I'll look into the trade data a bit more, even as those data appear to be last updated in 2004. Perhaps the benefit of including the trade data (if not his population/GDP data) is they offer GW coverage where CoW does not. Even then, the data are 20 years out of date.

[svmiller]

I'm probably going to close this soon. I already have the GDP data. The trade data were last updated in 2004 and I'm not sure of any recent/planned updates.