Chapter 2

Data Display, Summary and Manipulation

In God we trust; all others must bring data! (Attributed to W Edwards Deming)


Data are essential in the monitoring and improvement of processes and in the measure and control phases of Six Sigma projects. Such data are often obtained in time sequence. For example, a critical dimension might be measured every hour on each member of a sample of machined automotive components during production in a factory, the number of mortgage agreements completed successfully each day might be recorded by a building society. A run chart of such data can frequently be highly informative and forms the basis for some control charts. The construction of run charts using Minitab will be used to introduce the reader to the software and the key features of sessions, projects, worksheets, menus, dialog boxes, graphs, and ReportPad™, etc. The facility for calculation of derived data will also be introduced.

The use of histograms for the display of data will be described, and widely used summary statistics that indicate location and variability defined. The chapter concludes with consideration of a variety of methods for data entry in Minitab, of data manipulation and of the detection of missing and erroneous data values.

2.1 The Run Chart – a First Minitab session

2.1.1 Input of Data Via Keyboard and Creation of a Run Chart in Minitab

In their book Building Continual Improvement, Wheeler and Poling 1998, p. 31) introduce run charts as follows: ...

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