Bar Charts & Pictograms (Edexcel GCSE Maths)

Line Charts, Bar Charts & Pictograms

What is a line chart and what is it used for?

• Sometimes called a vertical line chart, this a visual way to represent discrete data
  

  • Line charts are used for numerical data (rather than categorical data)

    • They are particularly useful when there are lots of different options to show
      e.g.  Results of a test where scores are given as percentages

• The vertical axis shows the frequency

  • The scale should start at zero and increase in equal amounts

• The horizontal axis shows the different outcomes

  • A vertical line is drawn for each outcome and its height is its frequency

• You can easily identify the mode using a line chart
  

  • The mode is the most common outcome

  • This will be the outcome with the highest (tallest/longest) line

  • e.g.  In the line chart above, 11 was the modal test score, with a frequency of 7

• You can quickly see how the data is spread using a line chart

  • Lines may be crowded around a particular group of options with only a few elsewhere

  • This may help identify anomalies or outliers in the data

  • e.g.  In the line chart above we can see

    • the majority of the test scores, out of 20, were between 7 and 12

    • one pupil scored 19 out of 20, much higher than anyone else in the class

What is a bar chart?

• A bar chart is a visual way to represent discrete data

  • Discrete data is data that can be counted 

    • This can be numerical like shoe sizes in a class

    • Or non-numerical (categorical) like colours of cars down a road

• The horizontal axis shows the different outcomes

• The vertical axis shows the frequency

• The heights of the bars show the frequency

  • Bars should be separated by gaps

  • Bars should have equal widths

• The mode is the outcome with the highest bar

• You can also get dual bar charts to compare two data sets

  • Bars are in pairs (side-by-side) for each outcome

What is a pictogram?

• A pictogram is an alternative to a bar chart

  • It is used in the same situations

• There are no axes

  • Frequency is represented by symbols

  • A key shows the value of 1 symbol

    • For example, 1 symbol represents a frequency of 2

  • Half and quarter symbols are often used

• The pictogram above shows the shoe sizes of students in a class

  • As 1 picture of a shoe represents 2 students

    • Half a shoe represents 1 student

  • The number of students with a shoe size of 7, is 3