CHAPTER 17 More of a Good Thing: Multiple Regression 239
soon as your data are available in electronic format, you should run error-checks,
and generate summaries and histograms for each variable you plan to use in your
regression. You need to assess the way the values of the variables are distributed
as we describe in Chapter 11. And if you plan to analyze your data using multiple
regression, you need special preparation. Namely, you should chart the relation-
ship between each predictor variable and the outcome variable, and also the rela-
tionships between the predictor variables themselves.
Imagine that you are interested in whether the outcome of systolic blood pressure
(SBP) can be predicted by age, body weight, or both. Table 17-2 shows a small data
file with variables that could address this research question that we use through-
out the remainder of this chapter. It contains the age, weight, and SBP of 16 study
participants from a clinical population.
TABLE 17-2
Sample Age, Weight, and Systolic Blood Pressure Data for a
Multiple Regression Analysis
Participant ID
Age (years)
Weight (kg)
SBP (mmHg)
1
60
58
117
2
61
90
120
3
74
96
145
4
57
72
129
5
63
62
132
6
68
79
130
7
66
69
110
8
77
96
163
9
63
96
136
10
54
54
115
11
63
67
118
12
76
99
132
13
60
74
111
14
61
73
112
15
65
85
147
16
79
80
138