Methodology

Survey takers usually do not provide their real income figures to official researchers, a situation that results in underestimated income or a refusal to answer survey questions.

The National Bureau of Statistics (NBS) official study relies on random sampling that follows standard statistical procedures. There are several defects in this approach, namely that it lacks ways to persuade survey takers to provide confidential income information and a means to verify the data. The sampling is based on the principle of voluntary participation, whereas a considerable proportion of high-income people are unwilling to be included. The high-income earners who do participate are reluctant to provide accurate information about their income, especially "gray income" from unidentified sources.