Why and how innovations get adopted: A tale of four models

Scholars studying innovation have proposed several different models of the adoption process. This essay identifies two broad dimensions which differentiate the principal models: the strength of the evidence regarding an innovation's efficacy and the extent of increasing returns. In this essay, we propose that differences across these dimensions map to four models of the adoption/diffusion process prominent in the literature. We then analyze the diffusion patterns of six well-studied innovations in terms these variables, and discuss which models seems to fit them best.