We supplement the ‘Idea Production Function’ (IPF) with measures of R&D capital. We construct the R&D capital stock in the US, and estimate the IPF with patent applications as R&D output, allowing for a flexible treatment of R&D productivity (over 1968-2019). The estimated substitution...

We generalize the normalized Constant Elasticity of Substitution (CES) production function by allowing the elasticity of substitution to vary isoelastically with (i) relative factor shares, (ii) marginal rates of substitution, (iii) capital-labor ratios, or (iv) capital-output ratios. Ensuing...