Fractal analysis of time series in epidemiology: Is there information hidden in the noise?

Monthly total cancer incidence rates for women and monthly thyroid cancer incidence rates for women were retrieved from the Cancer Registry of Norway for the period 1953-2000, that is, 246-1061 cases per month and a total of 331 196 cases, and 0-24 female thyroid cases per month, a total of 5045, during this half-century. De-trended fluctuation analysis ad modum Peng et al., briefly explained in the article, are used to show that these two morbidity curves are statistical fractals, self-affine and non-Euclidean. The self-affinity parameter α = 0.87 of the female thyroid cancer curve indicates persistent long-range power-law time-correlations of the curve fluctuations. This finding indicates that exposure has occurred in the female population leading to the occurrence of thyroid cancer cases spread over a wide period. For the total female cancer curve, on the other hand, the self-affinity parameter α = 1.35 indicates time- correlations, but not the long-range, power-law type.