Boxplots
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Graph > Boxplot

Use boxplots (also called box-and-whisker plots) to assess and compare sample distributions. The figure below illustrates the components of a default boxplot.  

 

Outlier - an unusually large or small observation. Values beyond the whiskers are outliers.

 

By default, the top of the box is the third quartile (Q3) - 75% of the data values are less than or equal to this value.

 

 

 

 

By default, the bottom of the box is the first quartile (Q1) - 25% of the data values are less than or equal to this value.

 

 

By default, the upper whisker extends to the highest data value within the upper limit.

Upper limit = Q3 + 1.5 (Q3 - Q1)

 

 

 

Median - the middle of the data. Half of the observations are less than or equal to it.

 

By default, the lower whisker extends to the lowest value within the lower limit.

Lower limit = Q1- 1.5 (Q3 - Q1)

 

Note

By default, Minitab uses the quartile method for calculating box endpoints. To change the method for a specific graph to hinge or percentile, use Editor > Edit Interquartile Range Box > Options. To change the method for all future boxplots, use Tools > Options > Individual Graphs > Boxplots.

Dialog box items

One Y: Choose one of these options to display a separate graph for each column.

Simple

With Groups

Multiple Y's: Choose one of these options to display multiple columns of data on the same graph.

Simple

With Groups

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