^aTaxable income is not necessarily always the best measure from the perspective of tax efficiency. Piketty et al. (2014) argue that a reduction in the top income tax rate raises taxable income partly because, as taxation is reduced, high-income individuals put effort into negotiating a pay rise for themselves without otherwise working harder. In that case, the taxable income of some other individuals predictably falls. Their strongest empirical evidence for this mechanism concerns CEOs of large corporations, whose bargaining position is likely very different from that of most individuals affected by the top marginal tax rate in Finland.