# Plotting and Interpreting Statistical Diagrams

Students learn how to plot and interpret various statistical diagrams ranging from pie charts to  histograms with unequal class widths.  Throughout the unit emphasis is place on interpreting the diagrams as much as it is plotting them.

This unit takes place in Year 9 Term 3 and is followed by calculating statistical measures such as averages and range.

##### Prerequisite Knowledge
• Interpret and construct:
• frequency tables
• bar charts
• pictograms
• for categorical data.
• Construct and interpret stem and leaf diagrams
• Apply statistics to describe a population
##### Success Criteria
• Infer properties of populations or distributions from a sample, whilst knowing the limitations of sampling
• Interpret and construct tables and line graphs for time series data and know their appropriate useconstruct and interpret diagrams for grouped discrete data and continuous data, i.e. histograms with equal and unequal class intervals and cumulative frequency graphs, and know their appropriate use.
##### Key Concepts
• Students need to spend time interpreting the diagrams as well as creating them.
• When using pie charts to compare distributions the frequency of corresponding sectors is dependent on the total sample size.
• Frequency diagrams are used to represent discrete data whereas histograms are used for continuous data.
• Histograms with unequal class widths represent data with an unequal spread. Frequency is found using the area of a bar rather than its height.
• Cumulative frequency is the running total of the frequency.
• The interquartile range (IQR) shows the boundaries of where the most representative data is located.
##### Common Misconceptions
• Histograms are often confused with frequency diagrams.
• Students tend to be more competent with constructing the various representations than using them to analyse and make summative comments about distributions.

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