Question 1

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.

Accepted Answer

The new study's random assignment of treatments provides a more controlled and therefore convincing approach to understanding the effect of vitamins on colon cancer, while the earlier studies' results could be influenced by other factors related to lifestyle choices, such as eating lots of vegetables.

Question 2

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

Accepted Answer

When an observed effect is of a size that is unlikely to occur by chance, we call it a statistically significant effect. It means that the probability of obtaining the result by chance is very low. The other options do not fit the description given. The placebo effect refers to a response to a treatment that has no therapeutic effect. The confounding effect is when an extraneous variable affects the outcome of a study. The randomized effect is not a commonly used term in statistics.

Question 3

An experiment on the effect of vitamin A on cancer uses two randomly chosen groups of 200 men each, one given vitamin A and the other a placebo. An estimate from a similar experiment using two groups of 1000 men each would have

Accepted Answer

Larger sample sizes reduce variability in the estimates of the effects being studied, making the results more reliable and precise.

Question 4

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.
The explanatory variable in the study is

Accepted Answer

The explanatory variable in the study is birth weight because the researchers wanted to know if there is a specific birth weight below which infant death and illness increases sharply. The other options are not the focus of the study and do not serve as the explanatory variable.

Question 5

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.
Does the new study (properly designed) give good reason to think that vitamins prevent colon cancer?

Accepted Answer

The study did not find any significant difference among the groups in the formation of polyps in the colon that precede cancer, which means that taking these particular vitamins did not prevent colon cancer in the studied population. Therefore, the new study does not provide good evidence to support the idea that vitamins can prevent colon cancer.

Question 6

A magazine article on preventing cancer says, "Eating one serving of tofu a week may cut your risk of breast cancer 15%, recent research suggests."
If 15% is a statistically significant amount, then

Accepted Answer

If the 15% reduction in risk is statistically significant, it means that the results probably did not occur by chance. This does not necessarily mean that eating tofu prevents breast cancer or that the results of the study are false. However, it does suggest that there is a relationship between eating tofu and a lower risk of breast cancer. Additionally, the article does not provide enough information to determine whether the study was an experiment or not.

Question 7

A magazine article on preventing cancer says, "Eating one serving of tofu a week may cut your risk of breast cancer 15%, recent research suggests."
The data come from an observational study; therefore,

Accepted Answer

The answer of A magazine article on preventing cancer says,...

Question 8

Hearing loss is more common among premature infants than among full-term infants. This was thought to be an effect of premature birth. It has recently been suggested that hearing loss may be caused by the high noise level of the incubators in which the premature infants are placed. This is an example of

Accepted Answer

The suggested relationship between hearing loss and incubator noise level suggests that there may be a confounding variable at play; that is, the relationship between prematurity and hearing loss may not be as direct as previously thought, as it may be mediated by the noise level in the incubator.

Question 9

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)

Accepted Answer

This study is an observational study because the researchers did not intervene or manipulate any variables. Furthermore, the sample was not a probability sample as it only included infants born at Parkland Hospital in Dallas and excluded certain groups such as multiple births and infants with birth defects. Therefore, choice D is the best answer.

Question 10

One method that can be used to avoid problems with confounding variables in observational studies is to

Accepted Answer

Matching similar subjects from each of the study groups can help control for confounding variables by ensuring that the groups being compared are as similar as possible in terms of potentially influential factors. Randomly assigning subjects to study groups can also help control for confounding variables, but this option is typically not available in observational studies. Using very large samples can help increase the precision of the study results, but it will not directly address issues with confounding variables. Voluntary response sampling can introduce bias and is generally not recommended for observational studies.

Quiz 5: Experiments, Good and Bad

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

An experiment on the effect of vitamin A on cancer uses two randomly chosen groups of 200 men each, one given vitamin A and the other a placebo. An estimate from a similar experiment using two groups of 1000 men each would have

A magazine article on preventing cancer says, "Eating one serving of tofu a week may cut your risk of breast cancer 15%, recent research suggests." If 15% is a statistically significant amount, then

A magazine article on preventing cancer says, "Eating one serving of tofu a week may cut your risk of breast cancer 15%, recent research suggests." The data come from an observational study; therefore,

One method that can be used to avoid problems with confounding variables in observational studies is to