In this section, we learned about using graphs and tables for summarizing quantitative (numerical) data.
Quantitative variables can be summarized using frequency and relative frequency distributions.
Histograms are a graphical display of a frequency or a relative frequency distribution with class intervals on the horizontal axis and the frequencies or relative frequencies on the vertical axis. A frequency polygon is constructed as follows: for each class, plot a point at the class midpoint, at a height equal to the frequency for that class; then join each consecutive pair of points with a line segment.
Stem-and-leaf displays contain more information than either a frequency distribution or a histogram because they retain the original data values in the display. In a dotplot, each data point is represented by a dot above the number line.
The point of making graphs and tables is so that we may obtain information from them. We illustrate how to obtain useful information from the graphs and tables we have made in this section.
An image or distribution has symmetry (or is symmetric) if a line (axis of symmetry) splits the image in half, so that one side is the mirror image of the other. Nonsymmetric distributions with a long right-hand tail are called right-skewed, whereas those with a long left-hand tail are called left-skewed.