As discussed in the section on variables in Chapter 1, quantitative variables are variables measured on a numeric scale. Height, weight, response time, subjective rating of pain, temperature, and score on an exam are all examples of quantitative variables. Quantitative variables are distinguished from categorical (sometimes called qualitative) variables such as favorite color, religion, city of birth, and favorite sport in which there is no ordering or measuring involved.
There are many types of graphs that can be used to portray distributions of quantitative variables. The upcoming sections cover the following types of graphs:
- stem and leaf displays
- frequency polygons
- box plots
- bar charts
- line graphs
- scatter plots (discussed in a different chapter)
- dot plots
Some graph types such as stem and leaf displays are best-suited for small to moderate amounts of data, whereas others such as histograms are best-suited for large amounts of data. Graph types such as box plots are good at depicting differences between distributions. Scatter plots are used to show the relationship between two variables.