What are the differences between probability and nonprobability sampling? When is one more appropriate than the other?

Question

What will be an ideal response?

Answer 1

Probability sampling requires the specification of the probability that each sample element will be included in the sample. The process of random sampling consists of using a sampling frame and some random procedure of selection that makes probability estimation and the use of inferential statistics possible. Nonprobability sampling does not require the specification of the probability that each sample element will be included in the sample. Typically, nonrandom procedures are used to select sampling elements. Nonprobability sampling may not be representative of the population of interest, and therefore may not be generalizable to the population. Nonprobability sampling is much more convenient, less expensive, and less time-consuming than probability sampling and may be useful when probability sampling methods cannot be used.

Probability sampling methods are generally used at later rather than exploratory phases of research, when accuracy of samples is critical so that sample finding may be validly generalized to the population. Nonprobability sampling is often used in the early or exploratory stage of a study, where the purpose is to find out more information about the topic, discover interesting patterns, and generate hypotheses for later, more formal investigation. It is also used when data accuracy is not very important, when resources such as time and money are very limited, or when certain subjects are difficult to locate or access. Nonprobability sampling may also be used when there are very few population elements, when random sampling may not generate a representative sample, or when sampling based on expert judgment may be more reliable.