Statistics / Unit 1: Data and Displays
1.3 Frequency Tables and Relative Frequency
Notes
A frequency table lists each category with its frequency (count). The relative frequency is the fraction or percent of the total in each category.
- Relative frequency $\displaystyle = \frac{\text{count in category}}{\text{total count}}$.
- Relative frequencies add to $1$ (or $100\%$). Use them to compare groups of different sizes.
- Example: 40 students, 10 chose pizza. Relative frequency $\displaystyle = \frac{10}{40} = 0.25 = 25\%$.
| Lunch | Count | Relative frequency |
|---|---|---|
| Pizza | 10 | 0.25 |
| Tacos | 14 | 0.35 |
| Salad | 6 | 0.15 |
| Burgers | 10 | 0.25 |
Practice
In a survey of 40 students, 6 walk to school, 18 take the bus, 12 ride in a car and 4 bike. The relative frequency of riding the bus is:
$\displaystyle \frac{18}{40} = 0.45 = 45\%$.
In the same survey of 40 students (6 walk, 18 bus, 12 car, 4 bike), what percent walk or bike?
$\displaystyle \frac{6 + 4}{40} = \frac{10}{40} = 25\%$.
The relative frequencies of all categories of a variable should add to:
Every individual falls in exactly one category, so the parts make up the whole.
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