Chapter12 - Chapter 12 Sample Surveys A population is all...

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1 Chapter 12 – Sample Surveys A population is all individuals of interest to your study A sample is a subset of the population The sampling frame is a list of individuals from which the sample is drawn. For example, let’s say the population is all Santa Fe students, and a sample of 80 students is randomly selected from those students with local telephone numbers. In this case, the sampling frame is a list of students with local telephone numbers. Because not all students have a local telephone number, the sampling frame is not the same as the population being studied. In a perfect world, the sampling frame would match the entire population. But…the world is not perfect… Since populations are generally very large, it is time consuming and costly to collect data from all individuals in the population. In fact, it often impossible to even define who is in the population at any given time. Consider the population of all U.S. citizens. The Census Bureau tries to collect census data at the beginning of each decade. Collecting census data is inherently inaccurate because there are some people who refuse to return the census forms, others that cannot be contacted (homeless people, for example), and still others that are being born or dying each minute of every day. These are just a few of the many problems plaguing census data. Consequently, statisticians generally collect a random sample from the population being studied and use the sample results to draw conclusions about the entire population of interest. This technique is commonly referred to as inferential statistics (drawing inferences about the entire population using sample data). Although this may sound odd, inferences made from sample data are usually more accurate than census data. Why?
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Chapter12 - Chapter 12 Sample Surveys A population is all...

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