Seasonal parameters obtained from mortality data of two different sites ("a" and "b"). The time series in light blue represents three years of raw data, whereas the overlapped red curve represents the model trend and seasonality. In the last year of the series the primary peak and trough of each series are highlighted. The amplitude of the periodic annual function is obtained by dividing the wave height (difference between the peak and trough values) by the peak value. Despite the troughs of both “a” and “b” being similar, the standardized wave is much bigger in "a" (making it easier to infer that the resulting amplitude will be higher in "a"). Note that series "b" has a secondary peak - i.e. is a bimodal periodic annual function (the calculation of the amplitude for this secondary peak follows the same logic as that used for the primary peak).
Alonso and McCormick BMC Public Health 2012 12:982 doi:10.1186/1471-2458-12-982