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A statistical procedure where some individual units are chosen for study from a population (the total number of units) to make inferences about the entire population. A sample is chosen because it is usually not possible to include or study every member of the population (the universe). A sample is drawn from a population based on several factors, including the size of the sample needed and access to the population. There are a number of sampling methods, including random sampling, where each member of the population has an equal and known chance of being included in the sample. It is vital that the sample be representative of the population if inferences are to be made about the larger group.