Probability Sampling

In many scientific inquiries, it is impossible to individually appraise all the elements that comprise a population of interest. Instead, there is a need to infer collective properties of the whole population from a select subset of its elements. Probability sampling is an approach to selecting elements from a fixed population in such a way that

• 1.
  elements are selected by a random process,
• 2.
  every element has a nonzero chance of selection, and
• 3.
  [Page 1263]the relative frequency with which an element is included in a sample is deducible.

A collection of elements drawn in such a way is referred to as a probability sample. The first condition imparts a degree of objectivity to a probability sample and, in combination with the other two conditions, secures a basis for statistical inferences ...