Definition Random sample

A sample to be representative of a population must be random. In a random sample, the probability of ending up in the sample is the same for each element of a population. An example of a simple random sample is the drawing of a ball from a drum or tombola, such as the weekly lottery draw.

In a stratified random sampling, the elements of a population are divided into groups based on a previously determined attribute. Subsequently, a simple random sample is performed within each of those groups. An example would be the random selection of 100 residents from each of the 50 United States. 

Other methods of random samplings are cluster samples and multi-stage samples.

Please note that the definitions in our statistics encyclopedia are simplified explanations of terms. Our goal is to make the definitions accessible for a broad audience; thus it is possible that some definitions do not adhere entirely to scientific standards.