National income estimates can be used to compare a country's growth rate with that of another over a period of time.
National income estimates refer to the total income earned by a country's residents, including individuals, firms, and the government, in a given period, usually a year. By comparing the national income estimates of two or more countries over a period of time, analysts can determine which country is growing at a faster rate than the others.
This information is useful for making important economic decisions, such as determining which countries to invest in or which policies to implement. It also helps in assessing the level of development of a country's economy.
Therefore, the correct answer is "compare a country's growth rate with that of another over a period of time."