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# topic00 - Sampling without replacement is the usual and...

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Topic 0 Basic Concepts of Statistics 0.1 Population : The complete collection of Individuals that are of interest in the study. Sample: A portion, or part, of the population of interest. 0.2 Random sample: A random sample is a sample selected from a population so that: each population individual has the same chance of being selected as every other individual. That is, each possible sample(of the same size) has the same chance of being selected Example : How to have a random sample with sample size =2 from a group of 5 people? 0.3 Sample with replacement: Replace each sampled individual before picking next individual . The individual is placed back into the population for possible reselection Sample without replacement : A sampled individual is withheld from possibly being selected again in the same sample. Guarantees a sample of different units.
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Unformatted text preview: ## Sampling without replacement is the usual and customary sampling method 0.4 Finite/Infinite population: Finite if it is of fixed and limited size Finite if it can be counted even if very large; Infinite if it is unlimited Infinite if listing or counting every element is impossible 0.5 Sample without replacement from infinite population : Consider a infinite population, and two individuals A and B, get sample with size=2: In the first drawing, what is the chance you get A? If A is picked, but you don ’ t return it to the population, What is the chance you pick the B in the second drawing , what is the chance you get A again ? 0.6 Problems of Random Sample Under-coverage : Some of the population was excluded Non-response: When a sampled unit cannot be contacted or refuses to participate Response bias: Responses of selected units are not truthful...
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