Samples and populations

• The population is the entire collection of units about which we would like to ask questions, draw information and make claims.
• The sample is the collection of units that is actually measured or classified.
• A case is single object or individual to be measured (if numerical) or classified (if categorical).

Although any subset of a population can be considered as a sample, the purpose of the sample is to be representative of the population. The sample should be a small-scale replica of the population. In this way, any claims based on the sample can also confidently be made about the population.

A sample should be carefully planned in the context of the question being asked.