Skip to main content
Home
plus.maths.org

Secondary menu

  • My list
  • About Plus
  • Sponsors
  • Subscribe
  • Contact Us
  • Log in
  • Main navigation

  • Home
  • Articles
  • Collections
  • Podcasts
  • Maths in a minute
  • Puzzles
  • Videos
  • Topics and tags
  • For

    • cat icon
      Curiosity
    • newspaper icon
      Media
    • graduation icon
      Education
    • briefcase icon
      Policy

      Popular topics and tags

      Shapes

      • Geometry
      • Vectors and matrices
      • Topology
      • Networks and graph theory
      • Fractals

      Numbers

      • Number theory
      • Arithmetic
      • Prime numbers
      • Fermat's last theorem
      • Cryptography

      Computing and information

      • Quantum computing
      • Complexity
      • Information theory
      • Artificial intelligence and machine learning
      • Algorithm

      Data and probability

      • Statistics
      • Probability and uncertainty
      • Randomness

      Abstract structures

      • Symmetry
      • Algebra and group theory
      • Vectors and matrices

      Physics

      • Fluid dynamics
      • Quantum physics
      • General relativity, gravity and black holes
      • Entropy and thermodynamics
      • String theory and quantum gravity

      Arts, humanities and sport

      • History and philosophy of mathematics
      • Art and Music
      • Language
      • Sport

      Logic, proof and strategy

      • Logic
      • Proof
      • Game theory

      Calculus and analysis

      • Differential equations
      • Calculus

      Towards applications

      • Mathematical modelling
      • Dynamical systems and Chaos

      Applications

      • Medicine and health
      • Epidemiology
      • Biology
      • Economics and finance
      • Engineering and architecture
      • Weather forecasting
      • Climate change

      Understanding of mathematics

      • Public understanding of mathematics
      • Education

      Get your maths quickly

      • Maths in a minute

      Main menu

    • Home
    • Articles
    • Collections
    • Podcasts
    • Maths in a minute
    • Puzzles
    • Videos
    • Topics and tags
    • Audiences

      • cat icon
        Curiosity
      • newspaper icon
        Media
      • graduation icon
        Education
      • briefcase icon
        Policy

      Secondary menu

    • My list
    • About Plus
    • Sponsors
    • Subscribe
    • Contact Us
    • Log in
    • Plus Advent Calendar Door #14: What's average?

      14 December, 2016

      Most people have more than the average number of ears. This might seem odd, but it's true. The vast majority of people have two ears, but the few who have only one or none bring the average down to less than two. It's easy to illustrate this by imagining there are only five people in the world with one of them having only one ear. The average number of ears is

      2+2+2+2+15=95=1.8.
      Money

      What's the best way of measuring a population's income?

      The average (technically called the arithmetic mean) is computed by adding up the number of ears of all people in the world and then dividing by the total number of people. The example illustrates that the average isn't always the best measure to use when you want to make a wholesale statement about something. For example, a few super-high earners can drive up the average income in a population, giving the impression that people on the whole are much better off than they actually are.

      But luckily, there are other measures you can use that might be more appropriate. One is the median. You compute it by listing all the numbers in question (ears, income, etc) in order and picking the middle one. For example, if there are five people earning £1000, £1000, £3000, £3500 and £4000 a month, then the median is £3000. It tells you that roughly half the people earn less than that and the other half more (if there were an even number of people, the median would be the number lying exactly half-way between the middle two — in other words, it would be the arithmetic mean of the middle two).

      Alternatively, you could compute the mode. That's the number that appears most frequently in your list. In the example above the mode is £1000, telling you that most people in your list earn that amount. Or you might go for the midrange: add the smallest and the largest number and divide by two. In our example that gives (£1000+£4000)/2 = £2500. (Statisticians don't use the midrange very often though, partly because, like the arithmetic mean, it is easily skewed by outliers.)

      So, next time you hear an average quoted in the news, keep in mind that it may be misleading.

      You can find out more in the articles All about averages and Damn lies, or try our puzzle Meddling with averages.

      Return to the Plus advent calendar 2016.

      This article comes from our Maths in a minute library.

      • Log in or register to post comments

      Read more about...

      advent calendar 2016
      University of Cambridge logo

      Plus Magazine is part of the family of activities in the Millennium Mathematics Project.
      Copyright © 1997 - 2025. University of Cambridge. All rights reserved.

      Terms