The sales life cycle is used to describe the phases a product goes through from introduction to withdrawal from the market. The four phases are: (a) introduction, (b) growth, (c) maturity, and (d) decline and withdrawal. In the introduction phase, the firm relies on product differentiation to attract new customers to the product. In the growth phase, the product attracts competition, although differentiation is still an advantage for the firm. In the maturity phase, competition is keen, and cost control and quality considerations become important. In the final phase, differentiation again becomes important as do cost control and quality (see Chapter 13 and Chapter 18 for more detail).

Required
At which phases of the sales life cycle, if any, should investment-center evaluation methods be used, and why?