4.2 Drawing Scatter Diagrams

When drawing a scatter diagram, plot the variables along a pair of axes in the same way as you would for a line graph, the only difference being that you don’t (in fact can’t) join them up with a line. As usual, the variable which, it is suspected, is dependent on the other is plotted vertically and the independent variable is plotted horizontally.

Example 4.2a

This table shows the diameters (in inches) of a variety of cylindrical components produced on a lathe and the time taken (in seconds) by the machinist to make them.

Draw a scatter diagram to illustrate this.

Solution:
If anything, the time taken to make the component will depend on the diameter of the component (although they might both depend on something else), so we plot time vertically and diameter horizontally.
Component
Diameter
Time
A
3.006
195
B
3.012
205
C
3.001
200
D
2.998
185
E
3.015
210
F
3.009
215
G
3.013
200
H
3.000
190
I
2.997
195
J
3.005
205
K
3.010
200
L
3.016
220

The lowest diameter is 2.997 and the highest is 3.016, so a horizontal scale from 2.990 to 3.020 will suffice.

The lowest time is 185 and the highest is 220 so a vertical scale from 180 to 220 will do.