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Accounting for neighboring geospatial values in SAS

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Accounting for neighboring geospatial values in SAS

I originally asked this question on Stack Overflow/Exchange and was directed here. I don't remember if I posted this already (since the other post is likely in moderation if I did). If this is a double-post I apologize.

I'm trying to model the number of parks in a neighborhood as a function of education, land area (both continuous variables), and poverty perScentage (categorical). There may be other covariates included but for the sake of the question I will exclude them for now. I chose a Poisson model because to my understanding this is the model that is ideal for count data and my data has a lot of sampling zeroes.

My unit of analysis for the neighborhood is the census tract. Using ArcGIS, I joined geocoded point information about parks to a census tract shape file, exported this information into SAS, and generated counts. I then ran the following Poisson model.

proc genmod data = parks;

class povper / descending;

model cnt = povper edu area / link=log dist=poi;

run;

My issue with this model is that it doesn't take into account the number of parks in neighboring census tracts. I've been reading about possibly creating a spatially lagged dependent variable, but according to this answer, spatial lag and poisson don't necessarily mix. All of the census tracts in my table have x/y coordinates. Does anyone have advice on how I could incorporate the park counts from neighboring census tracts into my model using SAS?

Respected Advisor
Posts: 2,655

Re: Accounting for neighboring geospatial values in SAS

A possibility here would be PROC GLIMMIX, which allows for spatial covariance structures.  Check out the thread at

https://communities.sas.com/message/150416

where this is discussed, looking at counts.

Steve Denham

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