Statistics / Unit 1: Data and Displays
1.1 Individuals and Variables
Notes
Statistics is the science of learning from data. Data describe individuals (the people or things being studied) using variables (characteristics that can differ from one individual to the next).
- A categorical variable places each individual in a group or category, such as eye color, favorite sport or zip code.
- A quantitative variable is a number that makes sense to add and average, such as height or number of siblings.
- Quantitative variables are discrete (counts, like 0, 1, 2, 3) or continuous (any value in an interval, like time or weight).
- Numbers can be labels. Zip codes and jersey numbers are categorical because averaging them means nothing.
- Example: In a survey of students, favorite color is categorical, and height in centimeters is quantitative and continuous.
Practice
A spreadsheet has 200 rows (one per student) and columns for name, grade level and height. The individuals are:
Individuals are the people or things described; each row is one student.
Which variable is categorical?
Zip codes are labels. Adding or averaging them has no meaning.
The number of text messages a student sends in one day is:
It is a count (0, 1, 2, ...), so it is quantitative and discrete.
Ready for more? Take the Unit 1 test.