PSYC 2520 Chapter Notes - Chapter 9: Quota Sampling, The Literary Digest, Observational Error
1 Feb 2013
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Beginning behavioral research: a conceptual primer (7th ed. Opportunity samples are the first units that are available, whereas probability sampling plans use a random procedure for selecting a sample that is expected to be representative of the target population. However, to be absolutely sure that a sample is representative, we would have to know the true population value in advance, in which case (practically speaking) there would be no reason to study the sample. The term probability sampling implies that randomness enters into the selection process at some stage so that the laws of mathematical probability apply. Probability refers to the mathematical chance of an event"s occurring. Two important statistical requirements of a probability sampling plan are. A biased sample overestimates or underestimates the true population. An unstable sample is characterized by sampling units that vary greatly from one another (sample is highly variable) Generally speaking, the more homogenous the population, the fewer the sampling units needed.
