Question 1

Which of the following best describes the main difference between an observational study and an experiment?

Accepted Answer

An experiment deliberately imposes treatments on individuals to observe their response, while an observational study does not attempt to influence the response.

Question 2

In a study, researchers collect data on the dietary habits of 500 adults over the past 10 years to investigate the relationship between sugar intake and diabetes. What type of study is this, and why?

Accepted Answer

It is a retrospective observational study because it uses past data without influencing the subjects.

Question 3

A pharmaceutical company tests a new drug by randomly assigning 100 patients to receive either the drug or a placebo. After 6 months, they measure blood pressure in both groups. What is the response variable in this experiment?

Accepted Answer

The patients' blood pressure after 6 months

Question 4

In an experiment with two factors, Factor A has 3 levels and Factor B has 4 levels. How many different treatments are possible?

Accepted Answer

$$3 	imes 4 = 12$$

Question 5

Which of the following is a confounding variable in an experiment testing the effect of fertilizer on plant growth?

Accepted Answer

The amount of sunlight each plant receives, if not controlled

Question 6

Why is random assignment important in an experiment?

Accepted Answer

It reduces bias and allows for generalization of results to the population.

Question 7

A researcher wants to test if a new teaching method improves math scores. She randomly assigns 60 students to two groups: one uses the new method, the other uses the traditional method. After 3 months, both groups take the same test. Which principle of experimental design is illustrated by having more than one student in each group?

Accepted Answer

Replication

Question 8

In a double-blind experiment, who is unaware of which treatment each subject receives?

Accepted Answer

Both the subjects and the people in contact with them

Question 9

A study finds that people who exercise regularly have lower rates of heart disease, but the researchers did not assign exercise routines. What is the main limitation of this study?

Accepted Answer

It cannot establish a cause-and-effect relationship because it is observational.

Question 10

Which of the following best describes the placebo effect?

Accepted Answer

Subjects improve because they believe they are receiving the real treatment, even if they are not.

Question 11

A botanist grows 30 rosebushes in identical conditions and randomly assigns 15 to receive coffee grounds and 15 to receive none. After 3 months, she counts the number of roses on each bush. What is the experimental unit in this study?

Accepted Answer

The rosebushes

Question 12

Which of the following is a statistical disadvantage of using a very homogeneous group of subjects in an experiment?

Accepted Answer

It prevents generalizing the conclusions to a broad spectrum of subjects.

Question 13

In a clinical trial, 200 patients are randomly assigned to receive either a new medication or a placebo. Neither the patients nor the doctors know who receives which treatment. What is the primary purpose of this design?

Accepted Answer

To reduce hidden bias due to human expectations

Question 14

A researcher repeats an experiment several times and consistently finds that the treatment group has higher scores than the control group. What does this suggest about the results?

Accepted Answer

The results are statistically significant.

Question 15

Which of the following is NOT a principle of a well-designed experiment?

Accepted Answer

Retrospective analysis

Question 16

In an experiment, what is the main purpose of having a control group?

Accepted Answer

To provide a baseline for comparison to determine if the treatment has a causal effect

Question 17

A study tracks 200 men and women with high blood pressure over five years and finds they perform worse on memory tests than those with normal blood pressure. What type of study is this?

Accepted Answer

Prospective observational study

Question 18

Which of the following best describes blocking in experimental design?

Accepted Answer

Limiting the experiment to a homogeneous group to reduce variation in responses

Question 19

A sports science team randomly assigns cyclists to listen to music or silence during a workout and measures the distance traveled. What is the explanatory variable?

Accepted Answer

Whether the cyclist listened to music or silence

Question 20

Which of the following statements about the scope of conclusions from experiments is correct?

Accepted Answer

Results can only be generalized to populations similar to those in the study.

Experimental Design in Introductory Statistics: Observational Studies and Experiments

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