Key Concepts

• A stem-and-leaf plot is a graphical display for a small data set. Side-by-side stem-and-leaf plots can be used to compare two sets of data.
• Line graphs can be used to show changes in frequencies for quantitative data for discrete data sets.
• Bar graphs are used for comparing frequencies across categories in a data set.

Glossary

bar graph: a graph for displaying categorical data, where the length of the bar for each category is proportional to the number or percent of individuals in each category. Bars may be vertical or horizontal.

line graph: a graph for quantitative data where a the frequency of each value is recorded as a point and the frequencies are connected by line segments

outlier (extreme value): an observation that does not fit the rest of the data

quadrant: the sections created from intersecting x- and y-axes of the coordinate plane. Quadrants are named using the Roman numerals I, II, III, and IV, beginning with the top right quadrant and moving counter clockwise.

stem-and-leaf plot (stemplot): a graph for quantitative data where each value is split into two parts, the stem and the leaf.  The stem is usually a larger value, like tens and the leaves is usually a smaller value, like ones.  Note: Stem-and-leaf plots work better for small data sets of 50 values or less. The original data can often be reconstructed from stem-and-leaf plots.

side-by-side stem-and-leaf plot: a way to compare two different distributions by using a common stem.

x-axis: horizontal axis on a coordinate plane

y-axis: vertical axis on a coordinate plane