Grosswage illusion in a real effort experiment

In a controlled laboratory experiment, subjects had to fold letters in order to earn money. While the net income per letter was the same in the three treatments, the gross income varied and the tax rate was 0, 25% and 50%. Although work incentives should be the same in all treatments, subjects worked harder and longer when they were taxed. We conclude that this is due to a ‘gross-wage illusion effect’. The existence of this effect demonstrates that not only the tax rate and the tax base are of importance for work incentives, but also the perception of a tax.