Nuevas perspectivas sobre el Problema de la Unidad Espacial Modificable (PUEM) en relación con la representación cartográfica de enfermedades raras

This study analyses the effect of the modifiable areal unit problem (MAUP) comparing mortality data of a specific rare disease (Huntington) in three levels of spatial aggregation in Spain. The objective is to compare mortality indicators and cartographic visualisations in order to soundly advise on the optimal aggregation level according to population, covered area, and number of cases. We designed an adjacency ratio to observe the effect of neighbourhood relationships among three geographic units: province; district (comarca); municipality. For each level of aggregation, we performed epidemiological indicators of mortality as well as local indicators of spatial association. Maps were plotted with user-defined intervals to compare visual and statistical differences. MAUP-related effects are particularly noticeable in relatively infrequent events such as rare diseases. We found that district displayed the highest indicator for stability in the adjacency ratio and showed optimal characteristics for spatial resolution and the amount of information revealed through plotting. This helps in the choice of the working scale that can be used with other diseases or the levels of aggregation as a first step for more advanced epidemiological analyses.