Question 1

Use the following information for questions:
 Suppose you were to read about a study showing that people who sleep less than five hours a night have twice as much risk of a premature death as people who sleep seven or eight hours a night.
-Can you conclude that sleeping the shorter hours causes a higher risk of premature death?

Accepted Answer

The study described is observational, as it observes and reports on the sleep habits and outcomes of individuals without manipulating any variables. Therefore, it cannot establish causation, only correlation.

Question 2

Use the following information for questions:
 Suppose you were to read about a study showing that people who sleep less than five hours a night have twice as much risk of a premature death as people who sleep seven or eight hours a night.
-The "baseline risk"in this context is

Accepted Answer

The "baseline risk" refers to the standard or reference risk against which other risks are compared. In this context, it is the risk of premature death for people who sleep the normal amount of seven or eight hours a night, serving as the comparison group for those who sleep less.

Question 3

Use the following information for questions:
 Suppose you were to read about a study showing that people who sleep less than five hours a night have twice as much risk of a premature death as people who sleep seven or eight hours a night.
-Which of the following is not an example of a possible "confounding variable"in this study?

Accepted Answer

The amount of sleep a person gets per night is not a confounding variable in this study because it is the primary variable being investigated for its effect on the risk of premature death. Confounding variables are external factors that could affect the outcome, such as medications, alcohol consumption, or stress levels, not the main variable under study.

Question 4

A randomized experiment was done by randomly assigning each participant either to walk for half an hour three times a week or to sit quietly reading a book for half an hour three times a week. At the end of a year the change in participants' blood pressure over the year was measured, and the change was compared for the two groups.
-This is a randomized experiment rather than an observational study because

Accepted Answer

The key feature that distinguishes a randomized experiment from an observational study is the random assignment of participants to different groups or treatments, which helps to eliminate selection bias and allows for causal inferences.

Question 5

A randomized experiment was done by randomly assigning each participant either to walk for half an hour three times a week or to sit quietly reading a book for half an hour three times a week. At the end of a year the change in participants' blood pressure over the year was measured, and the change was compared for the two groups.
-The two treatments in this study were

Accepted Answer

The two treatments directly involve the activities participants were assigned to do, which are walking for half an hour three times a week and sitting quietly reading a book for half an hour three times a week. These are the interventions being compared in the study.

Question 6

A randomized experiment was done by randomly assigning each participant either to walk for half an hour three times a week or to sit quietly reading a book for half an hour three times a week. At the end of a year the change in participants' blood pressure over the year was measured, and the change was compared for the two groups.
-If a statistically significant difference in blood pressure change at the end of a year for the two activities was found, then

Accepted Answer

The experiment's random assignment of participants to either walking or reading activities controls for confounding variables and pre-existing conditions, allowing for a causal inference between the activity and blood pressure change.

Question 7

Which of the following is not a component of "Statistics"as defined in Chapter 1?

Accepted Answer

Statistics involves gathering, analyzing data, and making decisions under uncertainty, but it does not claim to turn uncertainty into certainty. It provides tools and methodologies to make informed decisions based on data, but inherent uncertainty always remains in statistical conclusions.

Question 8

Which of the following is true about a dotplot and a five-number summary?

Accepted Answer

A dotplot shows each individual data point, making it possible to see all responses. A five-number summary, which includes the minimum, first quartile, median, third quartile, and maximum, summarizes the distribution without showing each data point.

Question 9

The five numbers in a five-number summary are the

Accepted Answer

The five-number summary consists of the lowest value, lower quartile (Q1), median (Q2), upper quartile (Q3), and the highest value. These values help describe the distribution of a dataset.

Question 10

Student grade point averages (GPAs) are calculated by assigning a number to each letter grade earned, with A = 4, B = 3, C = 2, D = 1 and F = 0, then finding the average. A student proposes using the median of the numbers instead and calls this medGPA. A student has taken five courses (all an equal number of credit hours) and the grades were A, A, F, B, A. The usual GPA for these grades is 3.0. Should the student prefer using the median (medGPA)?

Accepted Answer

The median of the grades A, A, F, B, A (when converted to numbers 4, 4, 0, 3, 4 and then arranged in order) is 4, which corresponds to an A grade. Therefore, the medGPA would be 4.0, which is higher than the usual GPA of 3.0.

Question 11

A pop quiz in a class resulted in the following eight quiz scores: 0, 60, 66, 78, 82, 96, 98, 100. The five-number summary for these test scores is

Accepted Answer

The five-number summary consists of the minimum, first quartile (Q1), median, third quartile (Q3), and maximum. For these scores: minimum = 0, Q1 = 63, median = 80, Q3 = 97, maximum = 100.

Question 12

Which of the following is true about the use of sample surveys?

Accepted Answer

Sample surveys use data from a subset of the population (the sample) to make inferences or gain information about the entire population, not the other way around. The sample is designed to represent the population, but it does not include everyone in the population, nor is the population a subset of the sample.

Question 13

Which of the following is true about the margin of error for the most common types of surveys?

Accepted Answer

Increasing the sample size decreases the margin of error, making the survey results more precise.

Question 14

Suppose a Gallup Poll using a sample of 400 individuals found that 25% of them supported a particular opinion. An interval that is 95% certain to contain the truth about the population percent who support that opinion is

Accepted Answer

The correct choice is C because it reflects a reasonable margin of error for a sample size of 400. The other options underestimate the variability inherent in sampling. A 95% confidence interval for a proportion typically extends beyond just a fraction of a percent, especially with a relatively small sample size like 400.

Question 15

If a magazine sends a survey to a random sample of 10,000 of its subscribers but only 3000 of them return the survey, the sample results may not be representative of the population of subscribers because

Accepted Answer

The low response rate (only 3000 out of 10,000 surveyed subscribers responded) can lead to nonresponse bias, as the opinions of those who did not respond might systematically differ from those who did, affecting the representativeness of the survey results.

Question 16

In the study described in Case Study 1.4, questionnaires were sent to 100,000 women asking about love, sex and relationships. Only 4.5% of the women responded. This means that

Accepted Answer

Nonresponse bias is a significant concern when a large portion of the surveyed population does not respond, as their lack of response could be related to their views on the survey topics, potentially skewing the results.

Question 17

"Does Prayer Lower Blood Pressure" was a question asked in Case Study 1.5. The moral of the story was

Accepted Answer

Cause-and-effect conclusions cannot generally be made in an observational study because such studies do not control for all other variables that might influence the outcome, making it difficult to determine if the observed effect is truly due to the factor being studied or something else.

Question 18

If a difference seen in sample results is "statistically significant"it means that

Accepted Answer

Statistical significance indicates that the observed difference in sample results is unlikely to have occurred by chance if there is no actual difference in the population, suggesting that the observed difference is not due to random variation in the sample selection.

Question 19

An organization would like to conduct a survey of a sample of their membership to make conclusions about the entire membership. Given that they have a limited budget, they should focus their attention on

Accepted Answer

A representative sample is crucial for making accurate conclusions about the entire membership. It ensures that the sample reflects the diversity and characteristics of the whole group, leading to more reliable and valid results. Options A, B, and D may lead to biased or unrepresentative data.

Question 20

One of the common elements of the eight case studies in Chapter 1 is

Accepted Answer

In each case study, data is utilized to make informed judgments about the situation, highlighting the importance of data-driven decision-making.

Quiz 1: Statistics Success Stories and Cautionary Tales

Use the following information for questions: Suppose you were to read about a study showing that people who sleep less than five hours a night have twice as much risk of a premature death as people who sleep seven or eight hours a night. -The "baseline risk"in this context is