Sales of a product are assumed to follow an S-shaped curve, growing slowly in the early stages, achieving rapid and sustained growth in the middle stages, slowing up in the mature stage, and then declining. This should help in the selection of an appropriate forecasting method. For example, different methods should be used in the concept phase than in the test marketing. However, no empirical evidence exists for this claim. An analyst who has never heard of the product life cycle might still use an appropriate forecasting method.