HW Review: H1.3-1.5

Which of the following is used to summarize two potentially related categorical​ variables? Stacked table A​ two-way table Frequency table Histogram

A​ two-way table

Of the​ following, which is the only method of data collection suitable for making conclusions about causal​ relationships? A. Controlled experiments B. Anecdotes C. Observational studies D. All three are suitable.

A. Controlled experiments

Which of the following is NOT one of the criteria for the​ "gold standard" for​ experiments? A. Equal sample sizes for control and treatment group B. Large sample size C. Double-blinding, in which neither the subjects nor researchers know who is in which group D. Random assignment of subjects to treatment or control groups

A. Equal sample sizes for control and treatment group

In a 2017 study designed to investigate the effects of exercise on​ second-language learning, 40 subjects were randomly assigned to one of two​ conditions: an experimental group that engaged in simultaneous physical activity while learning the vocabulary in a second language and a control group that learned the vocabulary in a static learning environment. Researchers found that learning​ second-language vocabulary while engaged in physical activity led to higher performance than learning in a static environment. What features of a​ well-designed controlled experiment does this study​ have? Select all that apply. A. Random assignment B. A large sample size C. Double-blindedness D. Two-group division

A. Random assignment

Cartilage is a​ smooth, rubber-like padding that protects the long bones in the body at the joints. A study by Lu et. al. in Arthritis Care​ & Research found that women who drank one glass of milk daily had​ 32% thicker, healthier cartilage than women who did not. Researchers obtained information on milk consumption through questionnaires and measured cartilage through​ x-rays. In the​ article, research​ concluded, "Our study suggested that frequent milk intake may be associated with reduced OA progression in​ women." Does this study show drinking milk causes increased cartilage​ production? Why or why​ not? A. The study is an observational​ study, because there is no mention of random assignment.​ No, we cannot conclude causation when there is not random assignment. B. The study is a controlled​ experiment, because there is mention of random assignment.​ Yes, assuming that the results are​ significant, it would be reasonable to conclude causation because there is random assignment. C. The study is an observational​ study, because there is mention of random assignment.​ Yes, assuming that the results are​ significant, it would be reasonable to conclude causation because there is random assignment. D. The study is a controlled​ experiment, because there is no mention of random assignment.​ No, we cannot conclude causation when there is not random assignment.

A. The study is an observational​ study, because there is no mention of random assignment.​ No, we cannot conclude causation when there is not random assignment.

Why are percentages or rates often better than counts for making​ comparisons? A. Percentages are better than counts when there is categorical data. B. They take into account possible differences among the sizes of the groups. C. They are more accurate than counts. D. They are more statistically significant than counts.

B. They take into account possible differences among the sizes of the groups.

Indicate whether the following study is an observational study or a controlled experiment. A local public school​ encourages, but does not​ require, students to wear uniforms. The principal of the school compares the grade point averages of students at this school who wear uniforms with the GPAs of those who do not wear uniforms to determine whether those wearing uniforms tend to have higher GPAs. A. This is a controlled experiment. The principal separates the students into at least two​ groups, one of which is the control group. This is essential to conducting a controlled experiment. B. This is an observational study. The principal does not randomly assign students to either wear or not wear uniforms. Random assignment is essential to conducting a controlled experiment. C. This is a controlled experiment. The principal does not actually observe any characteristics of the​ students; the only data collected are the GPAs of the students. Observation in a natural environment is essential to conducting an observational study. D. This is an observational study. The principal does not assign a third party to identify the GPA of each student. Preventing bias so as to make the study​ double-blind is essential to conducting a controlled experiment.

B. This is an observational study. The principal does not randomly assign students to either wear or not wear uniforms. Random assignment is essential to conducting a controlled experiment.

Why is random assignment used to assign people to treatment groups and control groups in a controlled​ experiment? A. To ensure that the researchers do not know which groups subjects are members of. B. To make the groups as similar as​ possible, minimizing bias. C. To ensure that the groups have equal numbers. D. To make sure that the percentage of men and women in each group is exactly the same.

B. To make the groups as similar as​ possible, minimizing bias.

In a 2017 study designed to investigate the effects of exercise on​ second-language learning, 40 subjects were randomly assigned to one of two​ conditions: an experimental group that engaged in simultaneous physical activity while learning the vocabulary in a second language and a control group that learned the vocabulary in a static learning environment. Researchers found that learning​ second-language vocabulary while engaged in physical activity led to higher performance than learning in a static environment. What features of a​ well-designed controlled experiment are missing from this​ study? Select all that apply. A. Random assignment B. Two-group division C. A large sample size D. Double-blindedness

C. A large sample size D. Double-blindedness

A group of educators want to determine how effective tutoring is in raising​ students' grades in a math​ class, so they arrange free tutoring for those who want it. Then they compare final exam grades for the group that took advantage of the tutoring and the group that did not. Suppose the group participating in the tutoring tended to receive higher grades on the exam. Does that show that the tutoring​ worked? If​ not, explain why not and suggest a confounding variable. A. The study shows that the tutoring worked. B. Because this was an observational​ study, it only shows an​ association; it does not show that the tutoring worked. It could be that an insufficient number of students were studied to show that the tutoring worked. C. Because this was an observational​ study, it only shows an​ association; it does not show that the tutoring worked. It could be that more motivated students attended the tutoring and that was what caused the higher grades.

C. Because this was an observational​ study, it only shows an​ association; it does not show that the tutoring worked. It could be that more motivated students attended the tutoring and that was what caused the higher grades.

Two sections of statistics are​ offered, the first at 8 a.m. and the second at 10 a.m. The 8 a.m. section has 25​ women, and the 10 a.m. section has 15 women. A student claims this is evidence that women prefer earlier statistics classes than men do. What information is missing that might contradict this​ claim? A. The professor may be female in one class and male in the​ other, which could affect the female​ students' class preference. B. The age and class standing of the students is unknown. Older female students may prefer later​ classes, so it may be only younger female students who prefer earlier classes. C. The percentage of female students in the two classes is unknown. There may be more females in the 8 a.m. because there are more students in the 8 a.m. class than the 10 a.m. class. This claim could be true only if the classes were the same size. D. No information is​ missing, this claim is true.

C. The percentage of female students in the two classes is unknown. There may be more females in the 8 a.m. because there are more students in the 8 a.m. class than the 10 a.m. class. This claim could be true only if the classes were the same size.

Which of the following is a reason we can never draw​ cause-and-effect conclusions from observational​ studies? A.Researchers may be biased in the observations they choose to record. B.Observational studies often do not involve a large enough sample to draw​ cause-and-effect conclusions. C.Potential confounding variables may explain the differences between groups rather than the treatment variable. D.Observational studies are not scientific in nature.

C.Potential confounding variables may explain the differences between groups rather than the treatment variable.

Which of the following is an identifying mark of an observational​ study? A. Observational studies are controlled experiments. B. Subjects are often given a placebo or harmless pill that they believe is actually an effective treatment. C. Researchers observe but do not interact with subjects in an experiment. D. Subjects in the study are put into the treatment group or the control group either by their own actions or by the decision of someone not involved in the research study.

D. Subjects in the study are put into the treatment group or the control group either by their own actions or by the decision of someone not involved in the research study.

Patients with high blood pressure are asked to keep food diaries recording all items they eat for a​ one-week period. Researchers analyze the food diary data for trends. Indicate whether the study is an observational study or a controlled experiment. A. The study is a controlled​ experiment, because there is mention of random assignment. B. The study is an observational​ study, because there is mention of random assignment. C. The study is a controlled​ experiment, because there is no mention of random assignment. D. The study is an observational​ study, because there is no mention of random assignment.

D. The study is an observational​ study, because there is no mention of random assignment.

In an experiment studying the association between a treatment variable and an outcome​ variable, the group of people who do NOT receive the treatment are called​ what? The​ non-treatment group The control group The placebo group The treatment group

The control group

The outcome variable in a question about causality is also referred to as​ what? The response variable The predicting variable The treatment variable The control group

The response variable

A group of boys is randomly divided into two groups. One group watches violent cartoons for one​ hour, and the other group watches cartoons without violence for one hour. The boys are then observed to see how many violent actions they take in the next two​ hours, and the two groups are compared. The study is ...

a controlled experiment.

The number of times a value is observed in a data set is called a ...

frequency

In a 2017 study designed to investigate the effects of exercise on​ second-language learning, 40 subjects were randomly assigned to one of two​ conditions: an experimental group that engaged in simultaneous physical activity while learning the vocabulary in a second language and a control group that learned the vocabulary in a static learning environment. Researchers found that learning​ second-language vocabulary while engaged in physical activity led to higher performance than learning in a static environment. Assuming that the study was properly​ conducted, can we conclude that the physical activity while learning caused the higher performance in learning​ second-language vocabulary? Explain. The sample size of the study was ... , so we ... conclude that ...

small, should not, physical activity while learning caused higher performance.