Неравенство по налоговым данным

In most of the tasks about inequality that you might encounter, the data on income or wealth is given and is not questioned. In reality, however, the estimates of these numbers can be biased, and these biases can make an unjustified impression about whether inequality is high or low. Unjustified impressions, in their turn, may lead to unreasonable policy-making. In this task, we will discuss what these biases might be and where they can come from.

(a) (10 rp) Ann uses the administrative (tax) microdata to estimate the income inequality in country N. In particular, she takes the amounts of income tax paid by all households per year, calculates incomes dividing tax payments by the tax rates and gets the Gini coefficient based on this income distribution. Bob argues that due to this approach, Anna is likely to overlook a substantial part of the real income distribution. What part is it? Does this bias lead to overestimating or underestimating the extent of income inequality?