Summed probability distribution (SPD) of radiocarbon dates is commonly presented as a proxy for prehistoric demographic fluctuation. However, some skepticism remains.
The paper discusses a few problems based on the simulations of hypothetical radiocarbon dates. It is argued that SPD may generate misleading patterns when population size did not change over time, that summed probability and population fluctuation are not directly proportional, that the so-called “edge effect” makes it difficult to specify the times of population inflow and extinction, and that anomalous ups and downs in probability graphs are vulnerable to over-interpretation. The examination of archaeological SPD suggests that Chulmun population increased from ca. 4000 BCE. and decreased after 3000 BCE. However, the ratio of the summed probability is not likely to be correlated with the degree of demographic fluctuations. It also remains ambiguous when the Chulmun people first appeared and eventually vanished. The current analysis highlights that SPD is susceptible to false interpretation, and that the interpretation of SPD graphs should take into account the slope and shape of the 14C calibration curve.