A sizeable body of literature has been devoted to the diffusion of innovation. Research studies tend to fall into two broad categories; general diffusion research - an approach that seeks to understand the general process of diffusion and applied diffusion research - studies that describe the diffusion of specific products at particular moments in time or within given social communities. Collectively these studies suggest a certain regularity in the adoption process; initially few members adopt the innovation but over time, successive, overlapping waves of people begin to adopt the innovation. This pattern contributes to a generalised S-shaped curve, as shown in the figure at right. However, the exact shape and timing of curves varies in different product markets such that some innovations are diffused relatively quickly, while others can take many years to achieve broad market acceptance.