1.1 - Cases & Variables

When conducting a research study, information is collected concerning cases. Cases are also sometimes known as units or experimental units.

variable is a characteristic that is measured and can take on different values. In other words, something that can vary. This is in contrast to a constant which is the same for all cases in a study.

An experimental unit from which data are collected
Characteristic of cases that can take on different values (in other words, something that can vary)

Example: Student Data Section

Data are collected from a sample of STAT 200 students. Each student's major, quiz score, and lab assignment score is recorded.

The cases are the STAT 200 students. There are three variables: major, quiz score, and lab assignment score.

Example: Study Time & Grades Section

A third grade teacher wants to know if students who spend more time studying at home get higher homework and exam grades.

The third grade students are the cases. There are numerous variables: the amount of time spent studying at home, the homework grades, and the exam grades. 

Example: Dog Food Section

A researcher wants to know if dogs who are fed only canned food have different body mass indexes (BMI) than dogs who are fed only hard food. They collect BMI data from 50 dogs who eat only canned food and 50 dogs who eat only hard food.

The cases are the dogs. There are two variables: type of food and BMI.

Example: Chocolate Chip Cookie Section

Research question: What is the average weight of a chocolate chip cookie?

The cases are the cookies. The variable is weight.