1. 2. Heart attacks and height
2. Heart attacks and height. Researchers who examined health records of thousands of males found that men who died of myocardial infarction (heart attack) tended to be shorter than men who did not.
Is this an experiment? If not, what kind of study is it?
No, this is not an experiment. There are no imposed treatments. This is a retrospective observational study.
Is it correct to conclude that shorter men are at higher risk for heart attack? Explain.
We cannot conclude that shorter men are at a higher risk of heart attack. There may be lurking variables that are associated with both height and risk of heart attack.

2. 4. When spending large amounts to purchase advertising time, companies want to know what audience they'll reach. In January 2007, a poll asked 1008 American adults whether they planned to watch the upcoming Super Bowl. Men and women were asked separately whether they were looking forward more to the football game or to watching the commercials. Among the men, 16% were planning to watch and were looking forward primarily to the commercials. Among women, 30% were looking forward primarily to the commercials.
Was this a stratified sample or a blocked experiment? Explain.
This is a stratified sample. The question was about population values, namely the proportions of men and women who look forward to more commercials. No treatment was applied, so this is not an experiment.
Was the design of the study appropriate for the advertisers' questions?
Yes, the design was appropriate.

3. 6. Coffee stations in offices often just ask users to leave money in a tray to pay for their coffee, but many people cheat. Researchers at Newcastle Univer­sity replaced the picture of flowers on the wall behind the coffee station with a picture of staring eyes. They found that the average contribution increased signifi­cantly above the well­ established standard when peo­ple felt they were being watched, even though the eyes were patently not real.
Was this a survey, an observational study, or an experiment? How can we tell?
This is an experiment. The picture is the controlled factor. Randomization may have been used to decide which days each picture appeared.
Identify the variable.
The treatment was the picture behind the coffee station. The response variable was the average contribution.
What does "increased significantly" mean in a statistical sense?
The differences in money contributed were larger than could be reasonably attributed to usual day­ to­day variation.

4. For 7 – 18
whether it was an observational study or an experiment. If it was an observational study, identify (if possible)
whether it was retrospective or prospective.
the subjects studied and how they were selected.
the parameter of interest.
the nature and scope of the conclusion the study can reach.
If it was an experiment, identify (if possible)
the subjects studied.
the factor in the experiment and the levels.
the number of treatments.
the response variable measured.
the design (completely randomized, blocked, or matched).
whether h was blind (or double­blind).
the nature and scope of the conclusion the experiment can reach.

5. Among a group of disabled women aged 65 and older who were tracked for several years, those who had a vitamin B12 deficiency were twice as likely to suffer severe depression as those who did not.
whether it was an observational study or an experiment.
This is an observational study. The researchers are simply studying traits that already exist in the subjects, not imposing new treatments.
whether it was retrospective or prospective.
This is a prospective study. The subjects were identified first, then traits were observed.
the subjects studied and how they were selected.
The subjects were disabled women aged 65 and older, with and without a vitamin B­12 deficiency. The selection process is not stated.
the parameter of interest.
The parameter of interest is the percentage of women in each group who suffered severe depression.
the nature and scope of the conclusion the study can reach.
There is no random assignment, so a cause­and­effect relationship between B­12 deficiency and depression cannot be established.
The most that can be determined is an association, if this is supported by the data.

6. Researchers have linked an increase in the incidence of breast cancer in Italy to dioxin released by an industrial accident in The study identified 981 women who lived near the site of the accident and were under age 40 at the time. Fifteen of the women had developed breast cancer at an unusually young average age of 45. Medical records showed that they had heightened concentrations of dioxin in their blood and that each tenfold increase in dioxin level was associated with a doubling of the risk of breast cancer.
whether it was an observational study or an experiment. This is an observational study.
whether it was retrospective or prospective.
The study is retrospective. Results were obtained from pre­- existing medical records.
the subjects studied and how they were selected.
The subjects in this study were 981 women who lived near the site of dioxin release.
the parameter of interest.
The parameter of interest is difference in average lifespan between mothers of sons and daughters
the nature and scope of the conclusion the study can reach.
As there is no random assignment, there is no way to know that
the dioxin levels caused the increase in breast cancer. There may have been lurking variables that were not identified.

7. 7. Over a 4­month period, among 30 people with bipolar disorder, patients who were given a high dose (10 g/day) of omega­3 fats from fish oil improved more than those given a placebo.
whether it was an observational study or an experiment. This is an experiment, since treatments were imposed.
the subjects studied.
The subjects studied were 30 patients with bipolar disorder
the factor in the experiment and the levels.
The experiment has 1 factor (omega­3 fats from fish oil), at 2 levels (high dose of omega­3 fats from fish oil and no omega­3 fats from fish­oil).
the number of treatments.
The parameter of interest is the percentage of women in each group who suffered severe depression
the response variable measured.
There is no random assignment, so a cause­and­effect relationship between B­12 deficiency and depression cannot be established.
The most that can be determined is an association, if this is supported by the data.
the design (completely randomized, blocked, or matched). There is no information about the design of the experiment.

8. whether it was blind (or double­blind).
The experiment is blinded, since the use of a placebo keeps the patients from knowing whether or not they received the omega­4 fats from fish oils. It is not stated whether or not the evaluators of the “improvement” were blind to the treatment, which would make the experiment double­blind.
the nature and scope of the conclusion the experiment can reach. Although it needs to be replicated, the experiment can determine whether or not omega­3 fats from fish oils cause improvements in patients with bipolar disorder, at least over the short term. The experiment design would be stronger if it were double­blind.