Graphical Display of Data

This chapter introduces the analysis of SPC data through computer graphics with the help of the statistical software called eZ SPC. This is a simple program in the form of a spread-sheet with commands selected from a drop-down menu, very much like Microsoft Excel. The kind of data we run across in SPC problems can be categorized as qualitative and quantitative. To a statistician, qualitative data analysis is a less informative way to describe a set of data. Similar in function to the bar chart, the pie chart is a circular graph to show frequencies, but now the plot features the relative frequencies of the observations with regard to the other categories. The Pareto chart is a relatively new tool in SPC, but it is an old standby in economics. Histogram is a graphical display of frequency data with bars. With a histogram we can check the distribution of data. Controlled Vocabulary Terms bar chart; graphical model; histogram; pareto chart; pie chart