poverty lines defined as a proportion of the mean or median are strongly relative in the words of ravallion 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 indeed their proposed poverty schedule has elasticity zero for mean incomes up to usd a day and then elasticity rising from at usd 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