Affiliation: | 1. Université Paris‐Dauphine, LEDa, F‐75016 Paris, France (e‐mail: octavio.escobar@dauphine.fr);2. and IRD, UMR225‐DIAL, F‐75010 Paris, France;3. I would like to thank Fernando Borraz for providing useful data used on this paper. I am also grateful for comments from two anonymous referees that substantially improved the paper. |