  The density function of product life cycles in convenience stores is found to
follow the Weibull distribution. To clarify the parameters that determine these
life cycles, we introduce the conditional market share-defined as the
probability that a product is selected by customers only if it had been
previously purchased-and the market share without any conditions. The product
life cycle is more strongly correlated with the conditional market share of the
product than with the latter type of market share.
