Statistics is about using data to solve problems or make decisions. There are two types of data:

• Numerical data are expressed using numbers that can be put in order. For example, the question “How tall are the students in this class?” would involve measuring the height of each student, resulting in numerical data.
• Categorical data are expressed using characteristics. For example, the question “What brand of phones do people use?” would involve surveying several people, with their answers resulting in categorical data.

The question that you ask determines the type of data that you collect and whether or not there is variability in the data collected. In earlier grades, you learned that there is variability in a data set if not all of the values in the data set are the same. These are examples of statistical questions because they are answered by collecting data that have variability:

• “What is the average class size at this school?” would produce numerical data with some variability.
• “What are the favorite colors of students in this class?” would produce categorical data with some variability.

These are examples of non-statistical questions because they are answered by collecting data that does not vary:

• “How many students are on the roster for this class?” has only one possible answer. There is only one value in the data set, so there is no variability.
• “What color is this marker?” has only one answer. There is only one value in the data set, so there is no variability.