Technological-Knowledge Dynamics in Lab-Equipment Models of Quality Ladders

The Perpetual Inventory Model (PIM) assumes that, in each period, an arbitrary constant fraction of technological-knowledge stock is lost. By connecting the aggregate resource constraint with firms’ market value, we give a theoretical background to the PIM by showing that the technological-knowledge accumulation follows a dynamic process with an endogenous depreciation rate, which remains stable in steady state. Moreover, we relate different concepts of technological-knowledge used in the literature.