Exam 5: Experiments, Good and Bad

Confounding often defeats attempts to show that one variable causes changes in another variable. Confounding means that

A psychologist recently said that, "For relatively mild medical problems, the placebo effect will produce positive results in roughly two-thirds of patients." The placebo effect is

An observed effect that is of a size that would rarely occur by chance is called

An important reason for the use of randomization in designing experiments is that it tends to

A study compares the effect on college students of two different TV advertisements for spring break in Gulf Shores, Alabama. Call the ads "Ad #1" and "Ad #2." We want to know which ad makes more students want to visit Gulf Shores during spring break. The subjects are 90 students taking a course in hotel management. The design of the study looks like this: The statistical name for this study design is

A study compares the effect on college students of two different TV advertisements for spring break in Gulf Shores, Alabama. Call the ads "Ad #1" and "Ad #2." We want to know which ad makes more students want to visit Gulf Shores during spring break. The subjects are 90 students taking a course in hotel management. The design of the study looks like this: A weakness of this study is that

Do doctors in managed care plans give less charity care? Researchers chose 60 communities at random, then chose doctors at random in each community. In all, they interviewed 10,881 doctors. Overall, 77.3% of the doctors said they had given some care free or at reduced rates because of the patient's financial need in the month before the interview. Doctors who received at least 85% of their practice income from managed care plans were significantly less likely than other doctors to provide charity care. This study is a(n)

Were the extinctions that occurred in the last ice age more frequent among species of animals with large body sizes? A researcher gathers data on the average body mass (in kilograms) of all species known to have existed at that time. What are the explanatory and response variables?

Does taking vitamins prevent colon cancer? A study assigned 864 subjects at random to four groups. One group took beta-carotene, another took vitamins C and E, a third took all three, and the fourth group took only a dummy pill. After four years, there was no difference among the groups in the formation of polyps in the colon that precede cancer. Earlier studies had shown that people who choose to eat a lots of vegetables containing these vitamins tend to have less colon cancer.

A recent issue of the New England Journal of Medicine reports a study of all 122,754 infants born over an 8.5-year period at Parkland Hospital in Dallas, leaving out multiple births and infants with birth defects. The researchers wanted to know if there is a specific birth weight below which infant death and illness increases sharply. This study is a(n)