An important implication of "new growth" models is taht they exhibit "scale effects", meaning that variations in the levels of key variables such as the investment rate, research effort, and policy variables (tax rates) exert permanent influences on national growth rates.

In this paper we design two split-sample tests for subsets of structural coefficients in a linear Instrumental Variables (IV) regression. Sample splitting serves two purposes – 1) validity of the resultant tests does not depend on the identifiability of the coefficients being tested and 2) it...