Figure 5. (Rare) examples of a pronounced exogenous factor that affects first name dynamics.

Panel (a) shows three girls’ time series in which large and sudden changes are manifested. The two sharp rises in the frequency of Regnhild and Astrid in 1932 and 1933 are related to the birth of the princesses that carry these names at these years, correspondingly. The birth of prince Harald on 1937 explains the sudden popularity that this name gains in that year as shown in panel (b) for boys names. Fred (peace) became popular at the end of WWII, but we have no explanation for the dramatic rise of Emma on 2003.