Data Presentation (Edexcel International A Level Maths: Statistics 1)

What graphs and diagrams should I be familiar with?

• You will be expected to be able to use a variety of graphs such as:
  • Stem-and-leaf diagrams
    •  Can be used with ungrouped data of a single variable
    • Shows all the data and the shape of its distribution
  • Box plots
    • Can be used with ungrouped data of a single variable
    • Shows the range, interquartile range and quartiles clearly
    • Very useful for comparing data patterns quickly
  • Histograms
    • Can be used with continuous grouped data of a single variable
    • Can be used with varying group sizes
    • Shows the frequencies of the group, represented by the area of each bar
  • Frequency polygon

• • • Displays the shape of continuous grouped data
    • Created by joining the midpoints at the top of each bar of a histogram
  • Scatter diagrams
    • Can be used with ungrouped bivariate data (data for two variables)
    • Shows the pattern of the relationship between the variables

• You will not be expected to draw the graphs from scratch but you may be asked to add to a graph
  • You should make sure you know how to draw them anyway as it will help strengthen your understanding of the graphs

What should I look out for when interpreting graphs?

• Look carefully at the context of the information given in the graph
• Check the scales on both axes carefully, including units
  • Sometimes the numbers will be abbreviated to fit on the scale, for example if a population is given in millions then the number 60 will represent 60 000 000
  • Look carefully at the labels and units to determine how a value should be read
• If there is more than one graph represented on the same set of axes take extra care to ensure you are reading from the correct one
• Beware of misleading graphs, the scales on the axes, units and representation can be manipulated to make a graph look more/less convincing