Figure 4From: Varicella and Herpes Zoster in Madrid, based on the Sentinel General Practitioner Network: 1997–2004 Periodogram depicting the time series of cumulative varicella incidence. Madrid Region Sentinel General Practitioner Network: 1997–2004. The figure shows the periodicity of peaks in varicella incidence using a week as time unit. The peaks in periodogram reveal when the pattern repeats.Back to article page