Article: Sampling in health geography: reconciling geographical objectives and probabilistic methods. An example of a health survey in Vientiane (Lao PDR).Julie Vallée, Marc Souris, Florence Fournet, Audrey Bochaton, Virginie Mobillion, Karine Peyronnie, Gérard Salem[show abstract] [hide abstract]
ABSTRACT: Geographical objectives and probabilistic methods are difficult to reconcile in a unique health survey. Probabilistic methods focus on individuals to provide estimates of a variable's prevalence with a certain precision, while geographical approaches emphasise the selection of specific areas to study interactions between spatial characteristics and health outcomes. A sample selected from a small number of specific areas creates statistical challenges: the observations are not independent at the local level, and this results in poor statistical validity at the global level. Therefore, it is difficult to construct a sample that is appropriate for both geographical and probability methods. We used a two-stage selection procedure with a first non-random stage of selection of clusters. Instead of randomly selecting clusters, we deliberately chose a group of clusters, which as a whole would contain all the variation in health measures in the population. As there was no health information available before the survey, we selected a priori determinants that can influence the spatial homogeneity of the health characteristics. This method yields a distribution of variables in the sample that closely resembles that in the overall population, something that cannot be guaranteed with randomly-selected clusters, especially if the number of selected clusters is small. In this way, we were able to survey specific areas while minimising design effects and maximising statistical precision. We applied this strategy in a health survey carried out in Vientiane, Lao People's Democratic Republic. We selected well-known health determinants with unequal spatial distribution within the city: nationality and literacy. We deliberately selected a combination of clusters whose distribution of nationality and literacy is similar to the distribution in the general population. This paper describes the conceptual reasoning behind the construction of the survey sample and shows that it can be advantageous to choose clusters using reasoned hypotheses, based on both probability and geographical approaches, in contrast to a conventional, random cluster selection strategy.Emerging Themes in Epidemiology 02/2007; 4:6. · 2.59 Impact Factor
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ABSTRACT: Since Lao PDR opened up to free market economy at the beginning of the 1990s, public health care has coexisted with a private one, which is strongly growing. The phenomenon is particularly obvious in Vientiane. This article aims at studying the structures and motivations of the spatial distribution of each of the two systems in the capital. With this intention, we listed and located the whole of these offers in the urban area and interviewed the various sanitary administrations. It appears that the location of health care is prompted by very different motivations according to whether it is public or private: the first aims at controlling territories, the latter is mainly motivated by the financial contributions implied.