"The negative income tax involves a positive guarantee that has a pure income effect of reducing work effort. It also involves a tax increase on the earned income of recipients, and this has both an income and a substitution effect working in the opposite direction in their effect on work incentives. Consequently, we are unable to predict unambiguously the static, partial-equilibrium effects a negative income tax plan would have on work incentives." Is the last statement true or false? Explain your answers and show in a graph.