Sampling is a method to understand whole part by a little number of data. For example, quick news of election. I always wonder because the news is reported so quickly after the start of the vote.
"Sampling" is often introduced in "questionnaire". And sampling, the process to prepare data, is an important pre-process of Multi-Variable Analysis and Data Mining . And it is important to define levels and factors in Design of Experiments .
The points of sampling are stratification , clustering and randomness.
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