Chapter 13

For his Statistics class experiment, researcher J. Gilbert decided to study how parents' income affects children's performance on standardized tests like the SAT. He proposed to collect information from a random sample of test takers and examine the relationship between parental income and SAT score. a) Is this an experiment? If not, what kind of study is it? b) If there is relationship between parental income and SAT score, why can't we conclude that differences in score are caused by differences in parental income?

. 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. a) Is this an experiment? If not, what kind of study is it? b) Is it correct to conclude that shorter men are at higher risk for heart attack? Explain.

Multiple sclerosis (MS) is an autoimmune disease that strikes more often the farther people live from the equator. Could vitamin D-which most people get from the sun's ultraviolet rays - be a factor? Researchers compared vitamin D levels in blood samples from 150 U.S. military personnel who have developed MS with blood samples of nearly 300 who have not. The samples were taken, on average, five years before the disease was diagnosed. Those with the highest blood vitamin D levels had a \(62 \%\) lower risk of MS than those with the lowest levels. (The link was only in whites, not in blacks or Hispanics.) a) What kind of study was this? b) Is that an appropriate choice for investigating this problem? Explain. c) Who were the subjects? d) What were the variables?

When spending large amounts to purchase advertising time, companies want to know what audience they'll reach. In January \(2007, \mathrm{a}\) 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. a) Was this a stratified sample or a blocked experiment? Explain. b) Was the design of the study appropriate for the advertisers' questions?

Researchers studied the herb black cohosh as a treatment for hot flashes caused by menopause. They randomly assigned 351 women aged 45 to 55 who reported at least two hot flashes a day to one of five groups: (1) black cohosh, (2) a multiherb supplement with black cohosh, (3) the multiherb supplement plus advice to consume more soy foods, (4) estrogen replacement therapy, or (5) receive a placebo. After a year, only the women given estrogen replacement therapy had symptoms different from those of the placebo group. [Annals of Internal Medicine \(145: 12,869-897]\) a) What kind of study was this? b) Is that an appropriate choice for this problem? c) Who were the subjects? d) Identify the treatment and response variables.

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. (NY Times \(12 / 10 / 06)\) a) Was this a survey, an observational study, or an experiment? How can we tell? b) Identify the variables. c) What does "increased significantly" mean in a statistical sense? 7-20. What's the design? Read each brief report of statistical research, and identify a) whether it was an observational study or an experiment. If it was an observational study, identify (if possible) b) whether it was retrospective or prospective. c) the subjects studied and how they were selected.

Scientists at a major pharmaceutical firm investigated the effectiveness of an herbal compound to treat the common cold. They exposed each subject to a cold virus, then gave him or her either the herbal compound or a sugar solution known to have no effect on colds. Several days later they assessed the patient's condition, using a cold severity scale ranging from 0 to \(5 .\) They found no evidence of benefits associated with the compound.

Athletes who had suffered hamstring injuries were randomly assigned to one of two exercise programs. Those who engaged in static stretching returned to sports activity in a mean of \(15.2\) days faster than those assigned to a program of agility and trunk stabilization exercises. ( Journal of Orthopaedic \(\mathcal{E}\) Sports Physical Therapy 34 [March \(2004]: 3)\)

describes an experiment that showed that high doses of omega-3 fats might be of benefit to people with bipolar disorder. The experiment involved a control group of subjects who received a placebo. Why didn't the experimenters just give everyone the omega-3 fats to see if they improved?

Exercise 10 describes an experiment showing that exercise helped people sleep better. The experiment involved other groups of subjects who didn't exercise. Why didn't the experimenters just have everyone exercise and see if their ability to sleep improved?