4. Both the concentration and Herfindahl indices computed by the U. S. Bureau of Census tends to overstate the actual level. In addition, they understate the degree of concentration in local markets (gasoline, for example). Explain why we make these statements.

The use of data aggregation leads to overstatement of the  concentration and Herfindahl indices

while the use of National/state data leads to understatement of the degree of concentration in local markets.

Explanation:

The ratio of concentration and Herfindahl indices computed are mainly made up of foreign players while  the contributions of small local unorganized players are not considered, which leads to the increase in the value of  indices and ratios been used, ( i.e. The use of data aggregation ) .  hence the overstatement of the actual level.

The understatement of the degree of concentration in local markets happens because of the use of national and state data while computing the concentration in the local markets like gasoline and this is mainly caused by the presence of fewer industries in the market. The state and national data does not reflect the true concentration in the local market hence the degree of concentration is understated at the local level.