Minitab Express 2014: Comparative graphs and statistics
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Comparative graphs and statistics
To compare the shape, center, and spread of two distributions graphically, it is useful to show the two
graphs on the same horizontal scale. In statistical software, we do not do that by manipulating the
scales, but by choosing an option to make comparative graphs.
There are two complications to consider.


How the data on the two groups is given (in one column with a “group variable” value in another
column OR the two groups in separate columns.)
Whether the type of graph is available in a comparative mode, and, if so, whether it allows for
both ways the group data can be given.
In Minitab Express, the types of graphs on the left will only handle comparative graphs with the data in
one column and a “group variable” value in another column. The types of graphs on the right will
handle comparative graphs in both ways. The second way (separate columns) is called “multiple y’s.”
To compute comparative statistics, of course if the values are in separate columns, just compute the
statistics on each column. If the values are in one column, with a separate “group variable” then notice
that the “Descriptive Statistics” dialog box gives you the option to identify a group variable.
Minitab Express 2014: Comparative graphs and statistics
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Examples:
1.
Comparative dotplots for the percentage Democratic in 1980 for the Southern and nonSouthern states. After choosing Graphs > Dotplot > With Groups put the following into the
dialog box.
2.
Comparative summary statistics for the percentage Democratic in 1980 for the Southern and
non-Southern states. After choosing Statistics > Descriptive Statistics fill in the dialog box.
3.
Comparative boxplots for both years AND both groups of “Southern” and “Non-Southern.”
After choosing Graphs > Dotplots > Multiple Y variables > With Groups fill in the dialog box with
both variable names and the name of the Group variable.