Madeline M Brooks1, Scott D Siegel2, Anne E Corrigan3, Frank C Curriero3. 1. Institute for Research on Equity and Community Health (iREACH), Christiana Care Health System, 4000 Nexus Drive, Newark, DE 19803, United States. Electronic address: madeline.m.brooks@christianacare.org. 2. Institute for Research on Equity and Community Health (iREACH), Christiana Care Health System, 4000 Nexus Drive, Newark, DE 19803, United States; Helen F. Graham Cancer Center & Research Institute, Christiana Care Health System, Newark, DE, United States. 3. Department of Epidemiology, Johns Hopkins Spatial Science for Public Health Center, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, United States.
Abstract
BACKGROUND: Aggregating point-level events to area-level units can produce misleading interpretations when displayed via choropleth maps. We developed the aggregated intensity method to share point-level location information across unit boundaries prior to aggregation. This method was applied to tobacco retailers among census tracts in New Castle County, DE. METHODS: Aggregated intensity uses kernel density estimation to generate spatially continuous expected counts of events per unit area, then aggregates these results to area-level units. We calculated a relative difference measure to compare aggregated intensity to observed counts. RESULTS: Aggregated intensity produces estimates of event exposure unconstrained by boundaries. The relative difference between aggregated intensity and counts is greater for units with many events proximal to their borders. The appropriateness of aggregated intensity depends on events' spatial influence and proximity to unit boundaries, as well as computational inputs. CONCLUSIONS: Aggregated intensity may facilitate more spatially realistic estimates of exposure to point-level events.
BACKGROUND: Aggregating point-level events to area-level units can produce misleading interpretations when displayed via choropleth maps. We developed the aggregated intensity method to share point-level location information across unit boundaries prior to aggregation. This method was applied to tobacco retailers among census tracts in New Castle County, DE. METHODS: Aggregated intensity uses kernel density estimation to generate spatially continuous expected counts of events per unit area, then aggregates these results to area-level units. We calculated a relative difference measure to compare aggregated intensity to observed counts. RESULTS: Aggregated intensity produces estimates of event exposure unconstrained by boundaries. The relative difference between aggregated intensity and counts is greater for units with many events proximal to their borders. The appropriateness of aggregated intensity depends on events' spatial influence and proximity to unit boundaries, as well as computational inputs. CONCLUSIONS: Aggregated intensity may facilitate more spatially realistic estimates of exposure to point-level events.
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