Bar charts and pie charts turn a frequency table into a picture. Bar charts make comparisons between categories easy; pie charts show how one whole is divided. Switch between them, then see how a truncated axis can mislead.
Bar charts and pie charts both show how a categorical variable's individuals are split among categories. Switch views and see what each one makes easy to read.
A bar chart's vertical axis should start at 0, because readers compare bar heights. Raise the starting value and watch a small difference look huge.
One bar per category, height equal to its count or proportion. Bars are separated by gaps, and the vertical axis starts at 0.
Each slice's angle is its share of the whole. Use it only when the categories are parts of one whole that adds to 100%.
A bar chart can show frequencies or relative frequencies. The shapes are identical; only the axis labels change.
Describe categorical graphs by naming the most and least common categories and how much they differ. Don't use shape words like skewed.
Truncated axes, pictographs with growing areas, and 3-D effects distort comparisons. Readers compare areas and heights, so those must be proportional to the data.
Some categorical variables have a natural order (sizes, letter grades, agree to disagree). Keep that order on the graph.
Which graph fits, and what it is best at.
| Display | Best for | Rules | Avoid when |
|---|---|---|---|
| Bar chart (counts) | Comparing categories within one group | Axis from 0, gaps between bars, labeled axes | Comparing groups of different sizes |
| Bar chart (relative frequency) | Comparing groups of different sizes | Proportions add to 1 within each group | You need the actual counts |
| Pie chart | Showing parts of one whole | Slices must add to 100% | Categories overlap, many tiny slices, or close percents |
AP-style multiple choice. Pick an answer to see the explanation.
The vocabulary for topic 1.4. Read the list, flip through flashcards, or quiz yourself. For every term in the unit, see the Unit 1 terminology guide.