Dear Student,
The average income of a country is not increasing over period of time, but the records of National Income show a rise. This situation shows that the income of the people in the society is increasing. In other words that some sections of society are going economically stronger but we should remember that this development is happening in just some sections of the society not in all sections. So, there is lack of overall development in the country whereas the income is increasing. Because the average income shows the development in the country.
Regards.