Home » Further Maths Unit 3 & 4 » A1 - Data Analysis » 1.7 Box Plots and the Five Number Summary

1.7 Box Plots and the Five Number Summary

The Box Plot

  • The box plot is a graphical tool used to analyse the shape, spread and outliers of a numerical distribution.
  • It consists of a box with the bottom drawn at the value of quartile 1 and the top at quartile 3, a line drawn through the box at the median and a line either end of the box drawn to the lower and upper fences.
  • If the median line is in the middle of the box, the distribution is approximately symmetric, if it is drawn closer to the bottom of the box, it is positively skewed, if it is drawn closer to the top of the box, it is negatively skewed.
  • If the distribution has any outliers, they are represented as dots or crosses at their respective value along the y-axis and placed parallel to box.
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