Spatial Accessibility
2023-7-18
Spatial accessibility of pre-exposure prophylaxis (PrEP): different measure choices and the implications for detecting shortage areas and examining its association with social determinants of health
This paper compares different measures of spatial accessibility to pre-exposure prophylaxis (PrEP) clinics and finds Gaussian two-step floating catchment area (G2SFCA) provides the most consistent results for detecting shortage areas and examining associations with social determinants of health.
Abstract:
Purpose: We examine how various PrEP accessibility measures impact the detection of PrEP shortage areas and the relation of shortage areas to social determinants of health (SDOH).
Methods: Using ZIP Code Tabulation Areas (ZCTAs) in New York City as a case study, we compared 25 measures of spatial PrEP accessibility across four categories, including density, proximity, two-step floating catchment area (2SFCA), and Gaussian 2SFCA (G2SFCA). Bayesian spatial regression models were used to examine how PrEP accessibility is associated with SDOH.
Results: Using density to measure PrEP accessibility for small areas such as ZCTAs poses challenges to statistical modeling because the measured accessibility values are highly skewed with excess zeros, leading to the necessity of using complex models such as the two-part mixture model. When G2SFCA measures are used, which account for distance decay effects and the competition from the PrEP demand side, findings on PrEP shortage area detection and the association between PrEP accessibility and SDOH were more consistent and less sensitive to spatial scales (i.e., varying from 10- to 30-min driving).
Conclusions: This research adds to the nascent research on PrEP accessibility measurement and sheds lights on selecting an appropriate measure to assess spatial disparities in PrEP accessibility and its associations with SDOH.
Summary:
- Examines how different measures of PrEP accessibility impact detecting shortage areas and association with social determinants of health (SDOH)
- Uses ZIP Code Tabulation Areas (ZCTAs) in New York City as a case study
- Compares 25 measures across 4 categories: density, proximity, two-step floating catchment area (2SFCA), Gaussian 2SFCA (G2SFCA)
- G2SFCA accounts for distance decay and competition between supply and demand
- Weak correlation between some measures like density and 2SFCA at large scale
- Density poses modeling challenges due to skewness and excess zeros
- Spatial patterns and shortage areas sensitive to choice of measures and spatial scales
- G2SFCA findings on SDOH association more consistent across scales than 2SFCA
- Study demonstrates importance of appropriate measure selection for policy
Study questions and answers:
| Study Questions | Answers |
|---|---|
| What was the main objective? | Examine how measure choice impacts detecting PrEP shortage areas and association with SDOH |
| How many accessibility measures compared? | 25 across 4 categories |
| What is G2SFCA? | Gaussian 2SFCA, accounts for distance decay and supply/demand competition |
| What was a key finding? | G2SFCA gave more consistent results on SDOH across spatial scales |
| What city was used as a case study? | New York City |
| Why is this research important? | Highlights need for appropriate measure selection to inform resource allocation |