Variability of cancer risk within an area: time to complement the incidence rate

The aim of this study was to show that age-adjusted cancer incidence rates for an area may not be representative of the incidence in subareas. We propose a simple measure to show the amount of geographical variability. European age-standardized incidence rates (ASRs) for 'all sites excluding nonmelanoma skin cancer', for men, in 2014, for Nordic countries as a whole, for each country (Denmark, Faroe Islands, Finland, Greenland, Iceland, Sweden and Norway) and for their regions, were retrieved from the Nordcan with corresponding standard errors SEs. We compared the ASR for Nordic countries versus single country and single country versus specific regions. The overlapping of 95% confidence intervals was used for ASRs comparisons. As a measure of variability, we computed the range between the highest and the lowest ASR within an area and the ratio between this range and the ASR of the overall area, r/R=(range/ASR)×100. The 95% confidence interval of the ASR for Nordic countries as a whole did not overlap those of the majority of the single countries; in fact, the r/R - which provides a clue for the amount of underlying geographical variability - was rather large (57.1%). Within countries, the variability was negligible in Iceland (r/R=9.6%), whereas the highest value was found in Sweden (37.1%). The ASR does not provide any information on underlying geographical variability. Therefore, its interpretation could be misleading. When data for subareas are available, the r/R, which is simple to compute and to understand, should be added to the ASR for providing more truthful information.