In general, empirical studies on growth consider, at most, three factors, physical capital, labor and human capital. Land, however, is also a production factor for many activities. In this study, we make growth regressions considering land as factor. We also propose an explanation for why labor and capital shares do not seem to have a trend: It is possible that an increasing trend in physical capital share is compensated by a decreasing trend in land share. Similarly, an increasing trend in human capital share may be compensated by a decreasing trend in raw labor share. We find empirical support for the claim that the elasticity of output with respect to reproducible factors, human and physical capital, is positively correlated with the income level. This result has important implications for economic growth theory and for empirical exercises related to economic growth.
