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Statistical Process Control for Quality Improvement: A Training Guide to Learning SPC by James R. Evans - Department of Quantitative Analysis and Information Systems, College of Business Administration University of Cincinnati

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2 Measures of Location and Variability

In this chapter, we will discuss several important numerical measures for sample data that are used extensively in quality control. These numerical measures are often called sample statistics since they are computed from sample data. Measures of location describe the “centering” of the data; that is, they are used to represent the central value of the data. Measures of variability describe the “spread” of data. By spread, we mean how the data varies from the central value.

2-1. Simple Measures of Location

Three measures that are used most often to describe the central tendency of data are the mean, median, and mode. The mean of a set of data is simply the average value of the data. Let us use a simple ...

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