Chapter 4: Descriptive Statistics

This chapter provides some basic descriptive statistical techniques and introduces the reader to the usage of calculators .

OVERVIEW

Any manufacturing process includes the following factors:

• Method

• Machinery

• Materials

• Personnel

• Measurement

• Environment

Each of these factors may change, causing variation in the process and in the product. To decrease variation, information about the variation needs to be examined. The information, however, must be communicated either qualitatively or quantitatively. To do that, generally speaking, we begin with data and descriptive statistics.

Data are the input for everything we do in the improvement process. They are the raw material of all our analyses. If the data are questionable, then the results are not trustworthy. A more detailed discussion on data will be given in Chapter 7.

Descriptive statistics, on the other hand, are numerical summaries of data sets (frequency distributions). Measures of central tendency describe the location of the data sets. Measures of dispersion describe the spread (or variation) of data sets.