Introductory Biostatistics

Applying the formulas, we obtain estimates for the slope and intercept as
follows:

b 1 ¼

94 ; 322 
ð 1207 Þð 975 Þ= 12

123 ; 561 
ð 1207 Þ^2 = 12

¼
 1 : 74

x¼

1207

12

¼ 100 : 6

y¼

975

12

¼ 81 : 3

b 0 ¼ 81 : 3 
ð
 1 : 74 Þð 100 : 6 Þ

¼ 256 : 3

For example, if the birth weight is 95 oz, it is predicted that the increase be-
tween days 70 and 100 of life would be

yy^¼ 256 : 3 þð
 1 : 74 Þð 95 Þ

¼ 90 :1% of birth weight

Note: An SAS program would include these instructions:

DATA;
INPUT WEIGHT GAIN;
DATALINES;
112 63
111 66
...
103 90
94 91
;
PROC REG;
MODEL = WEIGHT;
PLOT GAINWEIGHT;

for which we will get the analysis as well as the scatter diagram.

Example 8.2 In Table 8.2 the first two columns give the values for age (x,in
years) and systolic blood pressure (y, in mmHg) for 15 women. We first let

SIMPLE REGRESSION ANALYSIS 287