She has conducted in-depth research ... a sample. Cluster sampling is a two-step sampling procedure. It may be used when completing a list of the entire population is difficult. For example ...

The number of observations in a population, the number of observations in a sample, and the procedure ... or a new product. Sampling distributions are used in statistics and research.

Proprietary research is not exempted. Methodologically, in all or nearly all cases, ABC News requires a probability-based sample, with high levels of coverage of a credible sampling frame.