Example of exploring data with brushing
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Suppose you want to look at the effects of several variables on blood pressure. After making three scatterplots, you brush points of interest to examine them in the context of each graph and set ID variables to learn more about these points.

Step 1: Create the Graphs

1    Open the worksheet PERU.MTW.

2    Choose Graph > Scatterplot > Simple > OK.

3    In the first row of Y variables, enter Pulse; in X variables, enter Years.

4    In the second row of Y variables, enter Systol; in X variables, enter Diastol. Click OK.

5    Choose Graph > Scatterplot > With Regression > OK.

6    In Y variables, enter Pulse; in X variables, enter Height. Click OK.

Step 2: Brush the outliers

In the first graph, two points are much higher on the Years scale than the rest. You want to see whether these two points are outliers in different graphs.

1    Choose Editor > Brush.

2    Drag the cursor to create a brushing region around those two points.

The brushing palette shows that rows 38 and 39 are associated with those points. Look at rows 38 and 39 in the Data window to see the values of other variables for these individuals.

Points in the other graphs that have the same row number are also brushed, allowing you to compare different characteristics visually. In the second graph, you see that neither of the brushed points appear to be outliers.

Step 3: Set ID variables

In the first two graphs, two points are much higher on the Years scale than the rest. You want to get more information on these two points.

1    Choose Editor > Set ID Variables.

2    Enter Age, Weight, Height, and Systol. Click OK.

With the added ID variables in the brushing window you can see information related to the brushed points not otherwise expressed in the graph. In the third graph,the brushed point near the regression line shows a subject with a height and weight that are very close to the general relationship between height and weight. Another subject (the second brushed point) is quite overweight which may contribute to his high pulse rate. Further exploration may reveal more about the cause of this subject's high pulse rate.