Poverty lines defined as a proportion of the mean or median are "strongly relative" in the words of Ravallion (2010), in the sense that the elasticity of the poverty line to mean income is unity. This property implies that a proportional increase in all incomes (or all levels of consumption) in an economy leaves the poverty measure unaltered (Ravallion and Chen, 2011). Indeed, their proposed poverty schedule has elasticity zero for mean incomes up to USD 1.95 a day and then elasticity rising from 0.5 at USD 1.95 a day up to an asymptotic value of unity. Indeed, when all incomes increase by a given proportion, the median increases by the same proportion.