7.1 Relationship Between Two Variables and the Scatter Plot 97Table 7.1 is a listing of systolic and diastolic pressure for 48 elderly
men. Figure 7.1 is a scatter plot of this data.
A scatter plot is used to portray the relationship between two vari-
ables. It displays the relationship by marking the data on a grid of ( X ,
Y ) pairs. This is a plot in Cartesian coordinates of the measurements X
and Y for the individual subjects. In the case of Figure 7.1 , X is the
Table 7.1
Systolic and Diastolic Blood Pressure for a
Sample of 48 Elderly Men
Subject
numberSystolic blood
pressureDiastolic
blood pressure
01 140 78
02 170 101
03 141 84
04 171 92
05 158 80
06 175 91
07 151 78
08 152 82
09 138 81
10 136 80
11 173 95
12 143 84
13 117 75
14 141 83
15 120 76
16 163 89
17 155 97
18 114 76
19 151 90
20 136 87
21 143 84
22 163 75
23 141 81
24 163 94