Boxplot

Use Boxplot to assess and compare the shape, central tendency, and variability of sample distributions and to look for outliers. A boxplot works best when the sample size is at least 20.

In This Topic

Continuous variables
Categorical variables (optional)
Layout
By variables
Whiskers and outliers
Custom percentiles
Y-scale
Variable display order

For information about data considerations, examples, and interpretation, go to Overview of Boxplot.

Continuous variables

Enter one or more numeric columns that you want to graph.

Categorical variables (optional)

Enter up to five columns of categorical data that define the groups. The first variable is the outermost on the scale and the last variable is the innermost.

Layout

Choose one of the following layout options.

Separate graphs for each continuous variable: Creates a separate boxplot for each column in the Continuous variables field.
Overlay continuous variables: Columns in the Continuous variables field are overlaid on a single boxplot.

By variables

Enter one or more grouping variables in By variables to create a separate boxplot for each level of the grouping variables. The columns that you enter can be numeric or text, and must be the same length as the columns in Continuous variables and Categorical variables. The y-scales for each variable are the same across the multiple boxplots.

Show all combinations

When you enter multiple By variables, Minitab enables the Show all combinations checkbox. Select this option to create a separate boxplot for each combination of groups created by the By variables. If you do not select this option, Minitab creates a plot for each group of each By variable.

For example, the first By variable has 2 groups, Male and Female, and the second By variable has 2 groups, Employed and Unemployed. If you select Show all combinations, Minitab creates 4 separate plots for the combinations of Male/Employed, Male/Unemployed, Female/Employed, and Female/Unemployed. If you do not select Show all combinations, Minitab creates 4 separate boxplots for Male, Female, Employed, and Unemployed.

Whiskers and outliers

The whiskers extend from either side of the box. The whiskers represent the ranges for the bottom 25% and the top 25% of the data values, excluding outliers.

Jitter outliers: If you have identical data values on your graph, outlier symbols could hide behind each other. Choose this option to move symbols slightly to reveal overlapping points.

Custom percentiles

With large data sets, where outliers are common, you can display custom percentiles instead of outliers to gather more information about the data. Custom percentiles occur outside of the interquartile box and typically occur in the tails of the distribution. In addition, lines are placed at the minimum and maximum values. By default, these percentile values are 0.5, 2.5, 10, 90, 97.5, and 99.5, but you can add, delete, or change them.

Y-scale

Select how you want to display the y-scale.

Original units: Use the original units of measure for numeric variables.
Standardized units: Convert different units of measure to a standard unit to make numeric variables comparable.
Same Y-scale: Make the Y-scale the same across multiple graphs.

Variable display order

Minitab uses the terms "innermost" and "outermost" to indicate the relative position of the scales for multiple levels of groups displayed on a graph. For a horizontal scale, outermost refers to the scale at the bottom of the graph, and innermost refers to the scale farthest from the bottom, closest to the horizontal axis. For a vertical scale, outermost refers to the scale to the far left, and innermost refers to the scale closest to the vertical axis.

Choose one of the following options when you have multiple Y variables with groups.

Categorical variables first, Y's below: Graph variables are the outermost groups and the categorical variables are the innermost groups.
Y's first, categorical variables below: Graph variables are the innermost groups and the categorical variables are the outermost groups.