Ok, I'm not sure if "wiggida wiggida wiggida wack" is a good thing or bad thing, but I do know that regression discontinuity is all about spatial jumps which made me think of a song from my youth, Jump by Kris Kross. I blog a lot about old fashioned regression discontinuity (also all about jumps!) so what's this about spatial RD? Nothing. It's pretty much the same thing except that the running variable is usually about distance from a border. Here's a nice description.
One example discussed in the blog entry: Imagine you want to know the causal impact of having access to an irrigation system that uses gravity for getting water from one place to another. Plots just below the canal receive access to irrigation, while plots just above the canal do not. By comparing plots just below or just above the canal, you can get at causal impacts of the canal.
So what's the difference between spatial RD and regular RD?
1. In regular RD, there's a single score that determines whether you're just above or just below the cutoff---let's say one test score determines whether you get into your college of choice or not. Spatial RD is often about distance so there's a longitude and latitude component.
2. If you use, let's say, county of residence to determine distance to a state border, some people in that county may be very close to the border and others quite farther away.
3. Speaking of exploiting distance from state borders---the problem is that there are often many policies that differ when you cross a state border, not just one.
Read the full blog entry for more details about practical issues when using spatial RD techniques.
Go off and search for those jumps! jumps! :)
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