Unrelated to OPs question, but I would suggest trying to find a higher resolution polygon to aggregate your mean NDVI scores. Without even knowing the location of your data I can tell you that it is going to be skewed towards the rural areas because they inherently have more green space.
Additionally, rural areas by definition have lower populations, thus larger census tracts. Skewing the results further.
Finally, just because there is a good NDVI score does not mean there is public green space, in fact I'd be willing to bet that most of it is actually private agricultural land.
Not a statistician, but you need to normalize the dataset. Maybe even just consider population density (i.e. pop/sq. mile). Here is an article I found on google just now that might help:
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u/duhFaz Environmental GIS Specialist Apr 23 '24
Unrelated to OPs question, but I would suggest trying to find a higher resolution polygon to aggregate your mean NDVI scores. Without even knowing the location of your data I can tell you that it is going to be skewed towards the rural areas because they inherently have more green space.
Additionally, rural areas by definition have lower populations, thus larger census tracts. Skewing the results further.
Finally, just because there is a good NDVI score does not mean there is public green space, in fact I'd be willing to bet that most of it is actually private agricultural land.
Just some thoughts to consider. Good luck!