Figure 1.

Time course of the incidence of stroke mortality in Minnesota during the span from 1950 to 1998, shown with 4-component model including a prominent circannual rhythm (top left). Least squares spectrum illustrates how prominent the circannual variation is, and indicates the presence of a weak second harmonic with a period of 6 months (top right). Reconstructed waveform of the circannual rhythm shows a peak incidence in winter (bottom left). Similar results are found for the incidence of all adverse cerebrovascular events in Khanty, Siberia, during the span from 2001 to 2014 (N = 2485), based on much fewer data collected from calls for an ambulance (bottom right). © Halberg Chronobiology Center.