Threats to Validity for Upcoming Chicago Green Space Reproduction
Embarking on my most individual reproduction study yet, I will be doing a final project for this class by attempting to reproduce the lab “Urban Environmental Justice of Green Space Access in Chicago” from the Human Geography with GIS class that I took last semester. This study assesses people’s access to green space designated by parks and forests in segregated neighborhoods of Chicago. A benchmark of 60% is used to create racial majority groups which is used as an indicator to assess which populations have the greatest access to greenspace.
While this is a relatively simple study, in good research practice it is still important to think about any possible threats to validity that could challenge the integrity of the results before conducting the study. The main threats to validity present themselves in the form of boundary effects, modifiable aerial unit problem, and spatial heterogeneity.
Boundary Effects: Restricted to the extent of the city of Chicago the hard boundary of the city’s border could cut off people along the edges who might access a park within 0.25 miles outside of the city making it seem like they have less access to green space than people within the city.
Modifiable Aerial Unit Problem: The population with access to green space is calculated based on block groups which is one of the smallest enumeration units. This decreases the chances that diversity in spatial trends is generalized. The racial majority groups are calculated at the tract level, however, which might ignore varying trends between racial majority groups at the block group level.
Spatial Heterogeneity: This poses an issue when looking at the differences in greenspaces. Not all greenspaces have the same amenities or quality for their communities to access–just because it technically counts as a greenspace does not mean it has the same inherent value as other greenspaces. The size of the greenspace presents a parallel problem. Since access to greenspace is determined by a constant buffer of 0.25 miles it does not account for the fact that smaller spaces can reach more people proportionally to the size of the green space. Perhaps smaller green spaces should have a smaller buffer since they do not have a proportional capacity of use when compared to larger parks with the same 0.25-mile buffer.
Once again, given the relative simplicity of this spatial analysis, it is negligible whether these threats to validity have a significant impact on the final results, however, as a GIScientist, it is my responsibility to consider their possibility, especially given the potential for this study to have the impact of highlighting racial disparities in environmental justice. The greatest of the above threats is the spatial heterogeneity of varying green space types. The following lab from this previous course attempts to address this threat by implementing new tree canopy raster data which is a great step forward if I can get that far.
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