While our method is not affected by biases introduced by regional differences in research intensity, the SPD could showcase spurious patterns if there is evidence of a temporally heterogeneous dating process
When examined on its own, we can consider a number of alternative causes that might have led to the observed fluctuations in the SPDs. A general time-dependent taphonomic loss would not affect our analyses (the exponential model mimics the process and the permutation-based comparison of the SPDs uses the observed 14 C dates directly, hence already integrating the effects of time-dependent loss), but a spatially divergent, inhomogeneous thinning process might produce some fluctuations that are not related to the underlying population dynamics. This problem is clearly not limited to SPDs and applies to all count-based time-series, but we are not aware of any study suggesting and quantifying this type of bias.
For instance, scholars might focus on dating sites of specific chronological interval rather than others, effectively leading to a higher density of 14 C dates
We are confident that this research bias is not affecting the samples from Hokkaido and Aomori Prefecture, but the strong interest in reconstructing the Middle Jomon pottery-sequence of the Kanto area might have generated a higher density of 14 C dates during this interval (see for instance ). This might indeed be the reason why we observe a strong positive deviation around 5,000 cal BP in Kanto. Read more