Dentifrice A: xA¼ 9 : 78
sA¼ 7 : 51
Dentifrice D: xD¼ 12 : 83
sD¼ 8 : 31Do the results provide strong enough evidence to suggest a real e¤ect of
fluoride inreducingthe mean DMFS?7.13 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, while animals in the control
group lived in isolation with no toys. After a month the experimental
animals were killed and dissected. Table E7.13 gives the cortex weights
(the thinking part of the brain) in milligrams. Use the two-samplettest
to compare the means of the two groups and draw appropriate con-
clusions.
TABLE E7.13
Treatment Control
707 696 669
740 712 650
745 708 651
652 749 627
649 690 656
676 642
699 6987.14 Depression is one of the most commonly diagnosed conditions among
hospitalized patients in mental institutions. The occurrence of depression
was determined during the summer of 1979 in a multiethnic probability
sample of 1000 adults in Los Angeles County, as part of a community
survey of the epidemiology of depression and help-seeking behavior. The
primary measure of depression was the CES-D scale developed by the
TABLE E7.14
CES-D Score
Cases xs
Male 412 7.6 7.5
Female 588 10.4 10.3276 COMPARISON OF POPULATION MEANS