Describing Variables (College Board AP® Statistics)

Study Guide

Naomi C

Written by: Naomi C

Reviewed by: Dan Finlay

Categorical & quantitative variables

What is categorical data?

  • Categorical data is data that is usually given in words and not numbers to describe something

    • It is also known as qualitative data

    • e.g. the colour of a teacher's car, a student's grade level, movie genres etc.

What is quantitative data?

  • Quantitative data is data that is given using numbers which count or measure something

    • e.g. the number of pets that a student has, the mass of a kitten, the time taken to run 100 m etc.

Discrete & continuous variables

What is discrete data?

  • Discrete data is quantitative data that uses a countable number of values

    • Discrete data takes specific values from a set of values

    • e.g. shoe size, 6, 6.5, 7, 7.5, 8, ... etc.

    • The number of values may be finite (e.g. integers from 1 to 5) or may be countably infinite (e.g. positive integers)

What is continuous data?

  • Continuous data is quantitative data that needs to be measured

    • Continuous data can take any value within a range of infinite values

      • e.g. the height of a student

    • Given any two values, it is always possible to find another value in between

      • e.g. 4.58 and 4.59 has 4.585 in between

When are variables discrete or continuous?

  • Some variables can be considered as discrete or continuous depending on the context and how it is defined

    • For example, age can be discrete or continuous

      • If you mean how many years old a person is then this is discrete

      • If you mean how long a person has been alive then this is continuous

  • When data is collected it is always collected in a discrete manner

    • However, when considering a model of the data, it is important to remember that it may be continuous

    • E.g. data may be collected on the length of leaf from a particular type of tree

      • The data collected may be measured to the nearest cm

      • but the data itself is continuous

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Naomi C

Author: Naomi C

Expertise: Maths

Naomi graduated from Durham University in 2007 with a Masters degree in Civil Engineering. She has taught Mathematics in the UK, Malaysia and Switzerland covering GCSE, IGCSE, A-Level and IB. She particularly enjoys applying Mathematics to real life and endeavours to bring creativity to the content she creates.

Dan Finlay

Author: Dan Finlay

Expertise: Maths Lead

Dan graduated from the University of Oxford with a First class degree in mathematics. As well as teaching maths for over 8 years, Dan has marked a range of exams for Edexcel, tutored students and taught A Level Accounting. Dan has a keen interest in statistics and probability and their real-life applications.