Question 1

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

Accepted Answer

In an observational study, researchers only observe and record data without manipulating variables, while in an experiment, they assign treatments to study their effects.

Question 2

A researcher wants to study the effect of a new drug on blood pressure. She randomly assigns 100 patients to receive either the drug or a placebo and measures their blood pressure after 6 weeks. What type of study is this?

Accepted Answer

Experiment

Question 3

Which principle of experimental design is best illustrated by randomly assigning subjects to treatment groups?

Accepted Answer

Randomization

Question 4

In a study investigating the relationship between smoking and lung cancer, researchers collect data from medical records of patients diagnosed in the past 20 years. What type of study is this?

Accepted Answer

Retrospective study

Question 5

Which of the following is a purpose of replication in experimental design?

Accepted Answer

To increase the reliability of results by applying treatments to multiple subjects

Question 6

A clinical trial is conducted to compare two therapies for insomnia. Patients are randomly assigned to either therapy A or therapy B, and neither the patients nor the evaluators know which therapy is being administered. What is this design called?

Accepted Answer

Double blinding

Question 7

Which of the following best describes a blocking variable in an experiment?

Accepted Answer

A variable that is used to group subjects so that treatments are applied within each group to control for its effect

Question 8

Suppose a researcher wants to study the effect of fertilizer type and watering frequency on tomato yield. She divides 24 tomato plants into groups based on soil type and applies all combinations of fertilizer and watering frequency within each group. What experimental design is she using?

Accepted Answer

Randomized Block Design (RBD)

Question 9

Which of the following is NOT a basic principle of experimental design?

Accepted Answer

Blinding

Question 10

A researcher wants to estimate the effect of a new teaching method on student performance. She selects two classes, applies the new method to one and the traditional method to the other, and compares test scores. What is a major concern with this design?

Accepted Answer

Lack of randomization may lead to confounding variables affecting the results

Question 11

Which formula represents the calculation of the mean of $$n$$ observations $$x_1$$, $$x_2$$, ..., x_n$$?

Accepted Answer

$$\frac{x_1$ + x_2$ + ... + x_n}{n}$$

Question 12

In a randomized block design, why is it important to apply all treatments within each block?

Accepted Answer

To ensure that the effects of the blocking variable are evenly distributed across treatments

Question 13

Which of the following scenarios best illustrates the concept of a confounding factor?

Accepted Answer

A study finds that people who exercise regularly have lower cholesterol, but fails to account for their diet

Question 14

Which of the following statements about statistical significance is TRUE?

Accepted Answer

A result can be statistically significant even if the difference is very small

Question 15

In the context of experimental design, what is the main purpose of blinding?

Accepted Answer

To prevent subjects and evaluators from knowing which treatment is being administered, reducing bias

Question 16

A researcher is studying the effect of two different diets on weight loss. She assigns 50 subjects to each diet and measures their weight after 3 months. She also records their exercise habits. Which variable is the response variable?

Accepted Answer

Weight after 3 months

Question 17

Which of the following best describes a prospective study?

Accepted Answer

Researchers follow subjects into the future to collect data as events unfold

Question 18

In a completely randomized design (CRD), what is the key assumption about the experimental units?

Accepted Answer

Experimental units are homogeneous and treatments are assigned randomly

Question 19

Which of the following is an example of controlling for a confounding factor in an experiment?

Accepted Answer

Measuring and adjusting for age in the analysis

Question 20

A researcher wants to study the effect of temperature and speed on the lifetime of electric motors. She tests motors at three different temperatures and three different speeds, applying all combinations. What type of experiment is this?

Accepted Answer

Two-factor factorial experiment

Observational Studies and Experimental Design in Statistics

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