Access to Health Services and Locating Health Services March 12, 2013

Haynes RM et al Effects of distances to hospital and GP surgery on hospital inpatient episodes, controlling for needs and provision. Social Science and Medicine 49(3):

from Athas WF et al Travel Distance to Radiation Therapy and Receipt of Radiotherapy Following Breast-Conserving Surgery. Journal of the National Cancer Institute 92(3):

Distance Decay function example

Firla 2007

Fulcher C, Kaukinen C Mapping and visualizing the location HIV service providers: an exploratory spatial analysis of Toronto neighborhoods. AIDS Care 17(3):

Firla 2007

Finding the shortest path

London Travel- Time Map

A.Walking only B.Car + walking C.Bus + walking D.Bicycle + walking Health care accessibility in southern Malawi Ray and Ebener, Int J Health Geographics 2008; 7: 63.

Klein et al., JAMA 2009; 302:

Dykstra’s shortest-path algorithm 1. Assign to every node a distance value: set it to zero for our initial node and to infinity for all other nodes. 2.Mark all nodes as unvisited. Set initial node as current. 3.For current node, consider all its unvisited neighbors and calculate their tentative distance. For example, if current node (A) has distance of 6, and an edge connecting it with another node (B) is 2, the distance to B through A will be 6+2=8. If this distance is less than the previously recorded distance, overwrite the distance. 4.When we are done considering all neighbors of the current node, mark it as visited. A visited node will not be checked ever again; its distance recorded now is final and minimal. 5.If all nodes have been visited, finish. Otherwise, set the unvisited node with the smallest distance (from the initial node, considering all nodes in graph) as the next "current node" and continue from step 3.

Shortest path example

Boscoe, Henry, Zdeb 2012

Mike Zdeb - Driving Distances and Drive Times using SAS and Google Maps: _SAS_and_Google_Maps Also: Boscoe FP, Henry KA and Zdeb MS. A Nationwide Comparison of Driving Distance Versus Straight Line Distance to Hospitals. Professional Geographer 2012; 64(2):

Fu LY et al Spatial accessibility to providers and vaccination compliance among children with Medicaid. Pediatrics 124:

Spatial accessibility = ratio of pediatric providers to pediatric population Provider density: Number of providers, weighted by specialty, smoothed with a Gaussian kernel density function of 3 miles Population density: Number of children under 18, using 2000 census block group data, smoothed over a 1 mile radius Results: Areas with the highest spatial accessibility had 36% more vaccination compliance than areas with the lowest spatial accessibility

Total population to be served = 10,000 Mean location = 6 Median location = 5 Modal location = 2 Range midpoint = 8

Allocation model – given a fixed set of facilities, figure out how to assign resources optimally Location model – identifies the best NEW location for a facility Location-allocation models do both of these things.

Smallman-Raynor MR, Muir KR, Smith SJ The geographical assignment of cancer units: patient accessibility as an optimal allocation problem. Public Health 112:

Predictions of NO and NO 2 concentrations. A location-allocation model was used to site the 102 air monitors. Criteria were (1) monitors should be in areas where pollution exhibits high variability (2) where population density is high Su et al. Environmental Research 2009; 109:

Bell 2013