Box plots
Five-number summary: min, LQ, median, UQ, max. Compare distributions.
Box plot displays minimum, lower quartile, median, upper quartile, maximum on a single number line. The box (LQ to UQ) is the IQR; whiskers extend to the extremes. Used to compare distributions side-by-side.
Worked examples
Min 12, LQ 18, median 22, UQ 26, max 35: box from 18 to 26, line at 22.
IQR = UQ − LQ.
Skewed if median isn't centred in the box.
Frequently asked questions
Outliers?
GCSE: above UQ + 1.5×IQR or below LQ − 1.5×IQR. Often shown as crosses outside the whiskers.
Comparing two box plots?
Compare medians (centre), IQRs (spread), and ranges. Always interpret in context.