Measures of Spread


the spread of a set of data can be measured using the range, quartiles, percentiles or the standard deviation.

the range is the difference between the highest and the lowest values.

the percentiles split a set of data into a hundred equal parts.

the standard deviation of a set of data is a measure of how each value differs or deviates from the mean.

Key Skills

  • calculate the range, quartiles and percentiles of a set of data
  • find the interquartile range for a set of data
  • calculate the standard deviation of a set of data using a table, spreadsheet or calculator.


spread, quartilelower quartileupper quartilemedianmean,percentile,
interquartile rangestandard deviation.