Skill: Collect categorical data

Categorical data place each observation into a group based on a quality or type, not a numerical measurement. Examples include favorite color, type of pet, or way of getting to school.

To collect categorical data:

1. Decide exactly what question to ask.
2. Choose categories that do not overlap.
3. Record one category for each person or object.
4. Use tally marks to count each category.
5. Count the tallies and write the frequency, or total number, for each category.

Example: A teacher asks 12 students, “How did you get to school today?”

The possible categories are:

• Walk
• Bus
• Car
• Bike

These categories are clear and non-overlapping because each student chooses the one method they used.

The students’ responses are:

$$\text{Bus, Car, Walk, Bus, Bike, Car, Bus, Walk, Car, Bus, Bike, Bus}$$

Now record each response with a tally mark.

Transportation	Tally	Frequency
Walk	$\vert \vert$	2
Bus	$\vert \vert \vert \vert /$	5
Car	$\vert \vert \vert$	3
Bike	$\vert \vert$	2

The tally marks show each response as it is recorded. A group of five is written as four vertical marks crossed by a fifth mark, making it easier to count.

The frequency column gives the total number of students in each category. Check the total:

$$2+5+3+2=12$$

Because the total is 12, every student’s response was recorded. This table can later be used to make a bar graph, with one bar for each transportation category.