How do fashion trends emerge evolve over time? Why were dresses with rectangular silhouettes all the rage in the 1920’s, followed by dresses with defined waists in the 1940’s? One theory is that some trends in fashion are influenced by trends in the economy. Specifically, the “hemline index” theory posits a connection between the economy and skirt lengths – skirts have gotten longer during some economically troubling times (such as the Great Depression) and shorter during some prosperous times (such as the 1920’s and 1960’s) 1.