The symmetric island model with D demes and equal migration rates is often chosen for the investigation of the consequences of population subdivision. Here we show that a stepping-stone model has a more pronounced effect on the genealogy of a sample. For samples from a small geographical region commonly used in genetic studies of humans and Drosophila, there is a shift of the frequency spectrum...

Empirically, teenagers who use alcohol or marijuana in one period are more likely to use hard drugs in the future. This pattern can be explained by a causal effect of soft drug consumption on future consumption of hard drugs (i.e., state dependence between drugs or stepping-stone effects) or by unobserved characteristics that make people more likely to use both soft and hard drugs (i.e., correl...