late the 95% confidence interval for the (population) mean di¤erence of
the LDL cholesterol level (mmol/L; cornflakes—oat bran).4.24 An experiment was conducted at the University of California–Berkeley
to study the psychological environment e¤ect on the anatomy of the
brain. A group of 19 rats was randomly divided into two groups. Twelve
animals in the treatment group lived together in a large cage, furnished
with playthings that were changed daily; animals in the control group
lived in isolation with no toys. After a month, the experimental animals
were killed and dissected. Table E4.24 gives the cortex weights (the
thinking part of the brain) in milligrams. Calculate separately for each
treatment the 95% confidence interval for the (population) mean of the
cortex weight. How do the means compare?
TABLE E4.24
Treatment Control
707 696 669
740 712 650
745 708 651
652 749 627
649 690 656
676 642
699 6984.25 The systolic blood pressures (mmHg) of 12 women between the ages of
20 and 35 were measured before and after administration of a newly
developed oral contraceptive (Table E4.25).
TABLE E4.25Subject Before AfterAfter–Before
Di¤erence,di
1 122 127 5
2 126 128 2
3 132 140 8
4 120 119 1
5 142 145 3
6 130 130 0
7 142 148 6
8 137 135 2
9 128 129 1
10 132 137 5
11 128 128 0
12 129 133 4182 ESTIMATION OF PARAMETERS