How Misleading is Linearization? Evaluating the Dynamics of the Neoclassical Growth Model

The standard procedure for analyzing transitional dynamics in non-linear macro models has been to employ linear approximations. This paper investigates the reliability of this procedure in evaluating the dynamic adjustments to policy changes or structural shocks. We analyze this issue using the example of a Ramsey growth model, with two alternative specifications of productive government spending. If government expenditure is introduced as a flow and the dynamic adjustment is fast, linearization may be a reasonably good approximation of the true dynamics even for fairly large policy shocks. If government expenditure assumes the form of a stock, leading to more sluggish adjustment, linearization is more problematic. It may yield misleading predictions, both qualitatively and quantitatively. These errors occur at the beginning of the transition and weigh heavily in welfare calculations. The implications for these errors for temporary shocks and the speed of convergence are also considered