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5 Descriptive Statistics

# 5 Descriptive Statistics - Dr Harvey A Singer School of...

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© 2002 by Harvey A. Singer 1 OM 210:  Statistical Analysis for Management Descriptive Statistics: An Overview Dr. Harvey A. Singer School of Management George Mason University

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© 2002 by Harvey A. Singer 2 The Problem Characterize and represent the population of interest. But … The population may be too big to conduct a full audit or census. It would take too much effort, time, or money, or all three, to survey everybody or everything in the population. The population may not be known yet. An ongoing process whose future performance is to be predicted now. The population is too complex to model from basic principles.
© 2002 by Harvey A. Singer 3 The Approach Need a shortcut method. Don’t directly characterize the population. Don’t even try to query everybody or everything in the population. Sampling and statistics is that shortcut. Statistics is supposed to make life easier, not harder.

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© 2002 by Harvey A. Singer 4 Why Sample? The population or process may be so large that to determine some quantity of interest for it may take too much money, time, and/or effort. Sample to avoid the expense of money, time, and effort. Market research for new products and services. Controlled experiments. The population or process may be so complex that it is too difficult to determine some quantity of interest from first principles. Sample as an end-run around first-principles understanding. Turbulence.
© 2002 by Harvey A. Singer 5 The Objective The objective of statistics is to be able to say something smart about a population based on just a sample of data in hand. That is, through a process of inductive reasoning, generalize results for the sample to the population. If the sample is representative of the population, then what is true for those sampled may be true for everyone or everything else that wasn’t sampled. Statistics is the approach for this inductive process of generalization.

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© 2002 by Harvey A. Singer 6 First Steps Before anything can be inferred about the population, must first know and understand the sample. “Understand” in terms of characterizing the sample in terms of representative values or ranges of values and patterns. Making inferences about the population will come later.
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5 Descriptive Statistics - Dr Harvey A Singer School of...

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