Fig. 3.

Prominent annual variation in natality data from Japan covering over 100 years (after detrending by second-order polynomials over four separate spans), seen by spectral peaks at frequencies of 1 cycle per year (100 cycles/100 years). Harmonic terms at two, three, and four cycles per year (vertical dashed lines) likely account for the circannual waveform. Note absence of spectral peak in the transyear region of the spectrum (around 75 cycles/100 years), by contrast to Fig. 1.