Smallpox and Season: Reanalysis of Historical Data

Figure 2

The spectral density plots for smallpox occurrences. (a)–(f) correspond to locations as chronologically ordered in Figure 1. A sharp peak at a period of 12 months corresponds to the annual cycle (seasonality), while other longer peaks may reflect a super-annual cycle (periodicity). No adjustment was made in drawing the plots.

(a)

(b)

(c)

(d)

(e)

(f)

(g)