StatisticalPlots`

BoxQuantile

is an option for BoxWhiskerPlot that specifies how far the box extends from the median.

Details and Options

To use BoxQuantile, you first need to load the Statistical Plots Package using Needs["StatisticalPlots`"].
Valid settings for BoxQuantile are numbers between zero and 0.5, with a default of 0.25.
With BoxQuantile->q, the box is drawn from the 0.5-q quantile to the 0.5+q quantile.

The default covers the middle 50% of the data:

Cover the middle 90%:

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