Access to Health Services and
Locating Health Services
March 12, 2013
Haynes RM et al. 1999. Effects of distances to hospital and GP surgery on hospital inpatient episodes, controlling for
needs and provision. Social Science and Medicine 49(3): 425-433.
from Athas WF et al. 2000. Travel Distance to Radiation Therapy and Receipt of Radiotherapy
Following Breast-Conserving Surgery. Journal of the National Cancer Institute 92(3): 269-271.
Distance Decay function example
Firla 2007
Fulcher C, Kaukinen C. 2005. Mapping and visualizing the location HIV service providers: an exploratory spatial
analysis of Toronto neighborhoods. AIDS Care 17(3): 386-396.
Firla 2007
Finding the shortest path
London TravelTime Map
http://www.mysociety.org/2006/travel-time-maps/
Health care
accessibility in
southern Malawi
A. Walking only
B. Car + walking
C. Bus + walking
D. Bicycle + walking
Ray and Ebener, Int J Health Geographics 2008; 7: 63.
Klein et al., JAMA 2009; 302: 1774-1781.
Klein et al., JAMA 2009; 302: 1774-1781.
Klein et al., JAMA 2009; 302: 1774-1781.
Dykstra’s shortest-path algorithm
1.
2.
3.
4.
5.
Assign to every node a distance value: set it to zero for our initial
node and to infinity for all other nodes.
Mark all nodes as unvisited. Set initial node as current.
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.
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.
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
Boscoe, Henry, Zdeb 2012
Mike Zdeb - Driving Distances and Drive Times using SAS and Google Maps:
http://www.sascommunity.org/wiki/Driving_Distances_and_Drive_Times_using
_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): 188-196.
Fu LY et al. 2009. Spatial accessibility to providers and vaccination compliance among children with Medicaid.
Pediatrics 124: 1579-1586.
Fu LY et al. 2009. Spatial accessibility to providers and vaccination compliance among children with Medicaid.
Pediatrics 124: 1579-1586.
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
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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. 1998. The geographical assignment of cancer units: patient accessibility as
an optimal allocation problem. Public Health 112: 379-383.
Predictions of NO and NO2 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: 657-670.
Bell 2013