Conventional or New? Optimal Investment Allocation across Vintages of Technology

This paper develops and analyzes a growth model that consists of complementary long-lived and short-lived vintage-specific capital. As a result of the existence of complementary capital that is vintage compatible but has different longevity, the model generates two distinct investment patterns: (i) if the rate of vintage-specific technological progress is above a threshold–which is the product of long-lived capital’s share and the difference in the rates of depreciation–then all new investment is allocated to the capital that embodies the frontier technology; (ii) otherwise, some investment is allocated to obsolete, short-lived capital to exploit the existing stock of obsolete long-lived capital. The result provides a new explanation for observed investment in obsolete technologies. An important implication of this result is that equipment price-changes do not necessarily reflect the rate of progress, since the prices of obsolete short-lived capital remain the same when the rate of the progress is slow enough (as mentioned in (ii) above). Another implication is that acceleration in the rate of vintage-specific technological progress can cause an abrupt reallocation of investment towards modern capital–consistent with investment booms that are concentrated in certain “high-tech” equipment.