Distinguishing groups in a scatterplot matrix

We described earlier how a scatterplot matrix can help to describe the relationships between 3 or more numerical variables. If each individual belongs to one of several groups, different symbols or colours can be used to distinguish the groups in the scatterplot matrix.

Swiss bank notes

The scatterplot matrix below shows four measurements that were made from 200 old Swiss 1000-franc bank notes. Two measurements describe the overall dimensions of the notes (the heights of the bills at their left and right edges) and two describe the printing within the bills (the heights of the margins at the top and bottom of the notes).

These data were actually collected to help distinguish forged bank notes from genuine ones, and half of the notes were know to be forgeries whereas the other half were genuine.

Click the checkbox Show Groups to display the different types of note. You should notice that ...

You may select points (with or without the brush) to further investigate this data set.