Defining Poverty Lines as a Fraction of Central Tendency

We show under lognormality that when the Gini coefficient is stable over time, defining the poverty line as a fraction of a central tendency of the living standard distribution restricts the evolution of the poverty measures to stability. That is, poverty does not change if the Gini coefficient does not change. Moreover, when the Gini coefficient slightly changes, most of the poverty changes can be considered a change in inequality. The consequences of using different poverty lines are then analyzed. Thus, important features in studies of poverty change based on these lines may result from methodological choices, rather than from economic mechanisms.