THE SIGMOIDAL INVESTMENT FUNCTION

Based on the investment theory of Abel and Eberly (1994), we develop an analytical model of adjustment costs, which produces a sigmoidal investment function. We also estimate the piecewise linear investment function, which includes as special cases linear models, models with one threshold, the original model of Abel and Eberly, which has two thresholds, and sigmoidal models. Empirical evidence clearly supports the sigmoidal model. The threshold estimate of Tobinfs q is 0.91. The investment ratio does not respond at value of Tobinfs q below 0.91, but begins to react sensitively as Tobinfs q passes 0.91.