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Open Access Research article

Optimizing the two-step floating catchment area method for measuring spatial accessibility to medical clinics in Montreal

André Ngamini Ngui12* and Philippe Apparicio2

Author Affiliations

1 Douglas Mental Health University Institute, 6875 Bld. Lasalle, Verdun, Montréal (Québec), H4H 1R3, Canada

2 Spatial Analysis and Regional Economics Laboratory, Université du Québec, Institut national de la recherche scientifique, Centre Urbanisation, Culture Société, 385 rue Sherbrooke est, Montréal (Québec), H2X 1E3, Canada

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BMC Health Services Research 2011, 11:166  doi:10.1186/1472-6963-11-166

Published: 11 July 2011



Reducing spatial access disparities to healthcare services is a growing priority for healthcare planners especially among developed countries with aging populations. There is thus a pressing need to determine which populations do not enjoy access to healthcare, yet efforts to quantify such disparities in spatial accessibility have been hampered by a lack of satisfactory measurements and methods. This study compares an optimised and the conventional version of the two-step floating catchment area (2SFCA) method to assess spatial accessibility to medical clinics in Montreal.


We first computed catchments around existing medical clinics of Montreal Island based on the shortest network distance. Population nested in dissemination areas were used to determine potential users of a given medical clinic. To optimize the method, medical clinics (supply) were weighted by the number of physicians working in each clinic, while the previous year's medical clinic users were computed by ten years age group was used as weighting coefficient for potential users of each medical clinic (demand).


The spatial accessibility score (SA) increased considerably with the optimisation method. Within a distance of 1 Km, for instance, the maximum clinic accessible for 1,000 persons is 2.4 when the conventional method is used, compared with 27.7 for the optimized method. The t-test indicates a significant difference between the conventional and the optimized 2SFCA methods. Also, results of the differences between the two methods reveal a clustering of residuals when distance increases. In other words, a low threshold would be associated with a lack of precision.


Results of this study suggest that a greater effort must be made ameliorate spatial accessibility to medical clinics in Montreal. To ensure that health resources are allocated in the interest of the population, health planners and the government should consider a strategy in the sitting of future clinics which would provide spatial access to the greatest number of people.

Spatial accessibility; medical clinics; health services; optimized two step-floating catchment area; Montreal