Box plots

Japanese school year: Junior high 2

What you learn

Learn how to construct boxplots using minimum, maximum, and quartile values to analyze data spread and compare multiple groups. By visualizing summary statistics, boxplots clearly illustrate the skewness and variability of distributions. This technique is widely utilized to compare trends across experimental and survey datasets.

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Key points

A boxplot is a chart used to visualize the spread and distribution of data at a glance. It is drawn using five key summary numbers: the minimum, $Q_1$ , the median, $Q_3$ , and the maximum.

This formula defines the length of the box in a boxplot. The difference between $Q_3$ and $Q_1$ (the $\mathrm{IQR}$ ) determines the box length, representing the range of the central 50% of data.

\mathrm{IQR} = Q_3 - Q_1

This provides a guide for reading data proportions from a boxplot. Roughly 50% of all data points lie inside the box, and each whisker holds approximately 25% of the data.

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Practice 1Coming soon