Students study median as a measure of center and interquartile range as a measure of variability. Students learn that these measures are preferred when the shape of the distribution is skewed. Students develop the idea that a measure of center provides a summary of all its values in a single number, while a measure of variation describes how values vary, also with a single number.
For students, box plots are the most difficult of the graphical displays covered in this module. This is because they differ from dot plots and histograms in that they are not really a display of the data but rather a graph of five summary measures (minimum, lower quartile, median, upper quartile, and maximum). For these reasons, box plots are introduced late in the module after the IQR and after students have already developed some fundamental understanding of data distributions, which is easier to do in the context of dot plots and histograms.
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