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A simple random sample is one in which each and every member of the population has an equal and independent chance of being selected. If the sample is large, this method is the best way yet devised to obtain a sample representative of the population of interest. Let’s take an example: Defi ne a population as all eighth-grade students in school district Y. Imagine there are 500 students. If you were one of these students, your chance of being selected would be 1 in 500, if the sampling procedure were indeed random. Everyone would have the same chance of being selected.

The larger a random sample is in size, the more likely it is to represent the population. Although there is no guarantee of representativeness, of course, the likelihood of it is greater with large random samples than with any other method. Any differences between the sample and the population should be small and unsystematic. Any differences that do occur are the result of chance, rather than bias on the part of the researcher

Fraenkel, J. R., Wallen, N. E., & Hyun, H. H. (2011). How to design and evaluate research in education. New York: McGraw-Hill Humanities/Social Sciences/Languages.