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      Comparing alternative approaches to measuring the geographical accessibility of urban health services: Distance types and aggregation-error issues

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          Over the past two decades, geographical accessibility of urban resources for population living in residential areas has received an increased focus in urban health studies. Operationalising and computing geographical accessibility measures depend on a set of four parameters, namely definition of residential areas, a method of aggregation, a measure of accessibility, and a type of distance. Yet, the choice of these parameters may potentially generate different results leading to significant measurement errors.

          The aim of this paper is to compare discrepancies in results for geographical accessibility of selected health care services for residential areas (i.e. census tracts) computed using different distance types and aggregation methods.


          First, the comparison of distance types demonstrates that Cartesian distances (Euclidean and Manhattan distances) are strongly correlated with more accurate network distances (shortest network and shortest network time distances) across the metropolitan area (Pearson correlation greater than 0.95). However, important local variations in correlation between Cartesian and network distances were observed notably in suburban areas where Cartesian distances were less precise.

          Second, the choice of the aggregation method is also important: in comparison to the most accurate aggregation method (population-weighted mean of the accessibility measure for census blocks within census tracts), accessibility measures computed from census tract centroids, though not inaccurate, yield important measurement errors for 5% to 10% of census tracts.


          Although errors associated to the choice of distance types and aggregation method are only important for about 10% of census tracts located mainly in suburban areas, we should not avoid using the best estimation method possible for evaluating geographical accessibility. This is especially so if these measures are to be included as a dimension of the built environment in studies investigating residential area effects on health. If these measures are not sufficiently precise, this could lead to errors or lack of precision in the estimation of residential area effects on health.

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          Most cited references 45

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          Revisiting the behavioral model and access to medical care: does it matter?

           John Andersen (1995)
          The Behavioral Model of Health Services Use was initially developed over 25 years ago. In the interim it has been subject to considerable application, reprobation, and alteration. I review its development and assess its continued relevance.
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            Place effects on health: how can we conceptualise, operationalise and measure them?

            In this paper we highlight what we consider to be a lack of adequate conceptualisation. operationalisation and measurement of "place effects". We briefly review recent historical trends in the study of the effects of place on health in industrial countries, and argue that "place effects" often appear to have the status of a residual category, an unspecified black box of somewhat mystical influences on health which remain after investigators have controlled for a range of individual and place characteristics. We note that the distinction between "composition" and "context" may be more apparent than real, and that features of both material infrastructure and collective social functioning may influence health. We suggest using a framework of universal human needs as a basis for thinking about how places may influence health, and recommend the testing of hypotheses about specific chains of causation that might link place of residence with health outcomes.
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              The concept of access: definition and relationship to consumer satisfaction.

              Access is an important concept in health policy and health services research, yet it is one which has not been defined or employed precisely. To some authors "access" refers to entry into or use of the health care system, while to others it characterizes factors influencing entry or use. The purpose of this article is to propose a taxonomic definition of "access." Access is presented here as a general concept that summarizes a set of more specific dimensions describing the fit between the patient and the health care system. The specific dimensions are availability, accessibility, accommodation, affordability and acceptability. Using interview data on patient satisfaction, the discriminant validity of these dimensions is investigated. Results provide strong support for the view that differentiation does exist among the five areas and that the measures do relate to the phenomena with which they are identified.

                Author and article information

                [1 ]Spatial Analysis and Regional Economics Laboratory, Université du Québec, Institut national de la recherche scientifique, Urbanisation, Culture et Société, 385 rue Sherbrooke est, Montréal (Québec), H2X 1E3, Canada
                [2 ]Department of Geography, Université du Québec à Montréal, Pavillon Hubert-Aquin, 1255 rue Saint-Denis, Montréal (Québec), H2X 3R9, Canada
                [3 ]Department of Social and Preventive Medicine, Faculty of Medicine, University of Montréal, P.O. Box 6128, Downtown Station, Montréal (Québec), H3C 3J7, Canada
                Int J Health Geogr
                International Journal of Health Geographics
                BioMed Central
                18 February 2008
                : 7
                : 7
                Copyright © 2008 Apparicio et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


                Public health


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