Statistics / Unit 1: Data and Displays
1.2 Bar Graphs and Pie Charts
Notes
A bar graph shows the count or percent for each category of a categorical variable.
- Bars have equal widths with gaps between them. The height shows the count or percent.
- Categories with no natural order can be rearranged without changing the message.
- A pie chart shows how a whole splits into parts. The slices must add to $100\%$.
- Central angle of a slice $=$ percent $\times\ 360^\circ$. Example: $25\%$ of $360^\circ$ is $90^\circ$.
- Use a pie chart only when the categories make up a whole. A bar graph works in more situations and is easier to compare.
Practice
In a survey, $15\%$ of students say they bike to school. In a pie chart, that slice has a central angle of:
$0.15 \times 360^\circ = 54^\circ$.
Which statement about bar graphs is true?
Bar graphs show categorical data. The gaps remind us that the categories are separate.
The slices of a pie chart of survey answers add up to $85\%$. The most likely problem is:
The parts of a whole must total $100\%$, so something was left out.
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