Comment on Chapters 3 and 4

Abstract

The two papers by Ansar et al. and by Muysken and van Zon (further referred to as AITU and MvZ respectively) extend existing putty-clay vintage labour demand models into different, though related, directions. AITU focus on long-run and short-run substitution possibilities between the production factors. The dual approach adopted allows the authors to test the often-used putty-clay, putty-putty or clay-clay production models against their maintained hypothesis of a putty-semi-putty model. The latter vintage model allows for both ex ante and ex post substitution possibilities, though the ex post substitution characteristics for each vintage are reduced by the ex ante choice of production technique. Nevertheless, for active vintages factor proportions are, among other things, influenced by actual factor prices.