Mining data cost-effectively

All statistical analysis requires gathering data.
Data may either be gathered for the entire target population, or only a portion or “sample.”
In most cases, gathering all data (population) is unrealistic in terms of cost and time. For example, if desiring to study the effects of an environmental cause on patients in the US it would be impossible to know everyone affected let alone locate them for inquiry.
Therefore, obtaining a selected portion of the population is more desirable for conducting such a study.
Sampling provides a most cost and time-effective means of mining such data.