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 Practice
Problems
These come from Dan Teague.
The Question: Suppose a dentist wants to know if a daily dose
of 500 mg of vitamin C will result in fewer canker sores in the mouth
than taking no vitamin C. Consider four scenarios.
1. The dentist, working though the local dental society,
convinces all of the dental patients in town with appointments in the
first two weeks in December to be subjects of a study. He divides them
into two groups, those who take at least 500 mg of vitamin C each day
and those who do not. He asks them how often they have canker sores in
their mouths and checks their dental record to see who has complained
of canker sores. He compares the proportion of those who take vitamin C
and complain about canker sores with the proportion of those who don’t
take vitamin C daily and complain of canker sores. There is a
significantly difference in the two proportions, with a significantly
smaller proportion of those taking vitamin C having canker sores. What
can we conclude?
2. The dentist, working though the local dental society, convinces all
of the dental patients in town with appointments in the first two weeks
in December to be subjects of a study. He randomly assigns half of them
to take 500 mg of vitamin C each day and half to abstain from taking
Vitamin C for three months. At the end of this time he determines the
proportion of each group that has suffered from canker sores during
those three months. There is a significant difference in the two
proportions, with a significantly smaller proportion of those taking
vitamin C having canker sores. What can we conclude?
3 The dentist, working though the local dental society, selects a
random sample of the dental patients in town and convinces them to be
subjects of a study. He divides them into two groups, those who take at
least 500 mg of vitamin C each day and those who do not. Then he asks
them how often they have canker sores in their mouths and then checks
their dental record to see who has complained of canker sores. He
comparers the proportion of those who take vitamin C and complain of
canker sores with the proportion of those who do not take vitamin C and
complain of canker sores. There is a significantly difference in the
two proportions, with a significantly smaller proportion of those
taking vitamin C having canker sores. What can we conclude?
4. The dentist, working though the local dental society, selects a
random sample of dental patients in town and convinces them to be
subjects of a study. He randomly assigns half of them to take 500 mg of
vitamin C daily for three months. At the end of this time he determine
that proportion of each group that has suffered canker sores during
those thee month. There is a significant difference in the two
proportions with a significantly smaller proportion of those taking
vitamin C having canker sores. What can we conclude?
Check your
answers.
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