Throughout this book, you have learned about variables. You have learned about random variables, discrete variables, continuous variables, numerical (or quantitative) variables, and categorical (or qualitative) variables. The various forms of graphical representations you have learned about in the previous chapters can be added to your learning of variables. The graphic below may help to summarize what you have learned.
Broken-line graphs, histograms, pie charts, stem-and-leaf plots, and box-and-whisker plots all represent useful (often very useful) tools in determining trends. Broken-line graphs, for example, allow you to show situations such as the distance traveled in specific time spans. Histograms use continuous grouped data to show the frequency trend in the data. Bar charts are a little different from histograms in that they use grouped discrete data, as do stem-and-leaf plots. Bar graphs, as you know, have gaps between the columns, while histograms do not. Stem-and-leaf plots are excellent for giving you a quick visual representation of data. Used for only smaller sets of data, stem-and-leaf plots are a good example of representations of grouped discrete data. Box-and-whisker plots are a final visual way of representing grouped data that you have learned about in the previous chapters. In a box-and-whisker plot, you are able to find the five-number summary to describe the spread of the data.
This chapter reviews graphs of the previous chapter, and adds four more complex graph types. The new types are summarized in the following table:
Graph Types Summary
|Double line graph
||Basic plot in two dimensions showing two different dependent variables on the same scale. The points are connected if the variable is continuous.
|Two-sided stem-and-leaf plot
||A graph that splits each data point from two sets into "stem" and "leaf". The middle column is all the stems, while either side are leaves from that stem in the two groups.
|Double bar graph
||A bar graph with two bars for each category or bin. The heights (vertical bars) or lengths (horizontal bars) represent the frequencies of each category.
|Double Box-and-whisker plot
||Two box-and-whisker plots set above the same line. For each, 50 percent of the data values are in the box, and the remaining 50 percent are divided equally on the whiskers.