11The identification strategy relies on two steps. In the first step, the effect of growth on urban concentration and on urban infrastructure is identified using rainfall as an instrument for growth. From these estimations residuals are obtained: Resid(UC) and Resid(G). These residuals have been “purged” from the reverse effect of growth. In the second step, the effect of urban concentration and the role of infrastructure is identified using these residuals. Standard tests were performed and support the relevance and validity of rainfall and rainfall squared as instrument for growth in the first step, and the relevance and validity of the residual variation in primacy and sanitation (once the reverse causality from growth has been removed) as instruments for actual primacy and sanitation in the second step.