Bar Charts & Pictograms (OCR GCSE Maths)

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 and what is it used for?

• A bar chart is a visual way to represent qualitative and/or discrete data
  • e.g.  colours of cars, shoe sizes, names of students
• A bar chart is very similar to a line chart
  • but tend to be used when there are only a small number of possible outcomes 
  • and tend to be used for categorical (non-numerical) data
• The vertical axis shows the frequency
  • The scale should start at zero and increase in equal amounts
• The horizontal axis shows the different outcomes
• Bars are used for each outcome and the height is the frequency
  • Each bar should have the same width
  • There should be a gap between each bar

• You can easily identify the mode using a bar chart
  • The mode is the most common outcome
  • This will be the outcome with the highest bar
  • e.g.  In the bar chart above, 10 is the modal shoe size with a frequency of 11 
• You can use a comparative bar chart to compare two (or more) data sets
  • For each outcome you would have a bar for each data set to show the frequencies
  • The bars for each data set for each outcome would be side-by-side with no gap
  • You would use colours or shading and a key to clearly show which bars belong to which data set

What is a pictogram and what is it used for?

• A pictogram is an alternative to a bar chart
  • It is a visual way to represent qualitative and/or discrete data
  • Like bar charts, pictograms tend to be used for categorical (non-numerical) data
• There are no axes on a pictogram
  • Frequency is represented by symbols
  • It is essential a key is included in a pictogram to state the frequency shown by one symbol
  • Half and quarter symbols are often used
• Pictograms should adhere to similar rules to bar charts to make them easy to read and interpret
  • All symbols should be the same size/shape
  • Symbols should be lined up so the highest frequency (the mode) and other features can be easily seen
• A pictogram for the shoe sizes of class 11A would look like this