Spencer, J. & Angeles, G. Health Serv Outcomes Res Method (2007) 7: 145. doi:10.1007/s10742-007-0022-7
Typically, accessibility ratios have been calculated through a simple mathematical division of the number of people in an area by the number of facilities (or staff) in that area. This approach does not take into account the service area of the facility or its proximity to population centers, and is often performed using aggregate numbers for an administrative region. This paper describes an approach to calculating accessibility ratios such as population to facility ratios or population to staff ratios using Kernel density estimation (KDE) within a geographic information system. KDE disperses discrete phenomena across continuous space and is unrestrained by administrative boundaries. Therefore it provides a better representation of the spread of people and services across the landscape. Two types of accessibility ratios are calculated on a national level for Nicaragua: population-per-facility and population-per-staff; the merits of using KDE over traditional approaches are discussed.