Why not use the entire population to draw our conclusions? This is a very good question that a smart researcher would ask. But when dollars are tight, human resources are limited, and time is of the essence, sampling is a wonderful option. And the reason is that for most purposes we can obtain suitable accuracy quickly and inexpensively on information gained from a sample.
The bottom line is it would be wasteful and foolish to use the entire population when a sample, drawn scientifically, provides accuracy in representing your population of interest. Assessing all individuals may be impossible, impractical, expensive or even inaccurate.
Here are some reasons why doctoral students should not even try to use the entire population in their dissertation research.
*We hardly ever know who makes up the entire population.
*It is too costly in terms of human resources and other expenses.
*It is time consuming and costly.
*There is alot of error to control and monitor.
*Lists are rarely up to date.