Evolutionary trends of industry variables

The paper offer's empirical evidence on the evolutionary trends of industry variables. It investigates the time path of patents, product price and quantity, and number of firms from the first introduction of a product to maturity of the market. The paper extends earlier work by Gort and Klepper by expanding the data on products through 1991, and augmenting it with new products and new data sources. The reexamination of the aging patterns reveal the Gort and Klepper results to be robust. The time trends follow the expected patterns with remarkable consistency and are strongly significant for most products. New evidence on patenting activity reveal an eventual decline in technological activity over the later years of the product market life-cycle. (C) 1998 Elsevier Science B.V.