Discussing the difference between random sampling and stratified random sampling. When is it most appropriate to use stratified random sampling techniques?

According to the U.S. Census Bureau (U.S. 2009.), the population of the United States is 307,196,751 and the population of the world is 6,778,171,325 people. One can see how expensive research could be to access every individual just in our country, not to mention the personnel resources and time needed to perform such a research study. Even if a researcher implements a study to a specific group, such as single mothers living in the Midwest, the number of individuals in this group would be astronomical to reach. . .

This article addresses: Discussing the difference between random sampling and stratified random sampling. When is it most appropriate to use stratified random sampling techniques?