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Managing and Improving Quality by Amar Sahay

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CHAPTER 5

Process Variation—How It Affects Product Quality

Introduction

Variation reduction is one of the major objectives of a quality program. Therefore, measuring variation is critical to reducing variation in the products and processes. One of the common ways of measuring variation in the data is by calculating the variance and standard deviation. The Greek letter σ2 (read as sigma-squared) represents the variance of a population data and σ represents the standard deviation. The corresponding symbols for the variance and standard deviation of a sample data are s2 and s. The standard deviation σ is a measure of spread or deviation around the mean. Larger the variation, more spread out the data is. Two or more sets of data may have the same ...

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