Time Series Graphs (Edexcel GCSE Statistics): Revision Note

Time Series Graphs

What is a time series graph?

• A time series graph is a type of line graph

  • A line graph plots data points, with successive points connected by lines

  • If time is plotted on the horizontal axis the line graph is called a time series graph

• A time series graph shows how a quantity (continuous data) changes over time

  • e.g. how the outside temperature changes during a week

• Measurements of the quantity are taken at particular times

  • Measurements should be taken at regular time intervals

• These are then plotted as points and joined together with straight lines

  • The lines help us to identify patterns in the data

• Time series graphs can show changes over short or long periods of time

  • e.g. changes to the temperature of two chemicals for the first few minutes after they've been mixed

  • or changes to the temperature of the earth over several years

How do I draw a time series graph?

• The horizontal axis (x-axis) will be the time axis

• The vertical axis (y-axis) will be the quantity being measured/recorded

• Plot the data as a series of points

  • Plot the points carefully

  • The points should be able to be plotted along the horizontal axis at regular intervals

    • otherwise the graph could be misleading

• Join one point to the next, in order, with straight lines

  • Use a ruler

• You should join the points with dashed lines if

  • you don’t know the values in between the data points

    • e.g. if the data is the amount of money in a club’s bank account at the start of each month

  • the parts of the graph in between the points are meaningless

    • e.g. if the data points are the number of ice creams sold on each day of the week

    • the parts of the graph between Monday and Tuesday (for example) don’t mean anything

  • Dashed lines will usually be appropriate for the time series graphs seen on the exam