Local standardized incidence ratio estimates and comparison with other mapping methods for small geographical areas using Slovenian breast cancer data

Abstract

Cancer maps are important tools in the descriptive presentation of the cancer burden. The objective is to explore the advantages and disadvantages of mapping methods based on point data in comparison with maps based on aggregated data. Four types of maps were prepared based on the same underlying data set on breast cancer incidence in Slovenian females, 2002–2004. First, the standardized incidence ratios (SIR) by municipalities are mapped in a traditional way. Second, two maps applying widely used smoothing methods are presented, both based on aggregated municipalities’ data: floating weighted averages and the Bayesian hierarchical modelling. Finally, the new alternative method based on exact cancer cases and population coordinates is applied – called the local SIR estimates. The decreasing west to east trend is visible on all map types. Smoothing produced more stable and less noisy SIR estimates. The map of the local SIR estimates emphasizes extremes, but unlike the map, based on the observed SIR, these estimates are statistically stable, enabling more accurate evaluation. The main advantages of local SIR estimates over the other three methods are the abilities of revealing more localized patterns and ignoring the arbitrary administrative borders. The disadvantage is that the geocoded data are not always available.

Keywords:

• cancer
• small-area mapping
• exploratory spatial analysis
• spatial smoothing
• standardized incidence ratio

Acknowledgements

The collaboration and dialogue with Finnish colleagues prof. Eero Pukkala and Toni Patama, MSc, from Finnish Cancer Registry, and Kari Pasanen, MSc, from University of Kuopio, Department of Environmental Sciences is sincerely appreciated. Many thanks to Prof. Anuška Ferligoj (Faculty of Social Sciences, University of Ljubljana) and prof. Vera Pompe Kirn (Cancer Registry of the Republic of Slovenia) for their encouragement and critical revision of the text.