Question 1

Which of the following best describes the purpose of randomization in an experiment?

Accepted Answer

To ensure that the treatment groups are as similar as possible with respect to both known and unknown variables.

Question 2

A researcher wants to test the effect of two different fertilizers on plant growth. She randomly assigns 50 plants to each fertilizer group and ensures all plants receive the same amount of water and sunlight. Which principle of experimental design is she applying by keeping water and sunlight constant?

Accepted Answer

Control

Question 3

In a clinical trial, patients are grouped by age (under 50, 50 and over) before being randomly assigned to treatments. What experimental design principle is being used?

Accepted Answer

Blocking

Question 4

Which of the following statements about replication in experiments is TRUE?

Accepted Answer

Replication allows us to estimate the variability of responses and increases the reliability of results.

Question 5

A student wants to test if two brands of sunscreen protect equally well. She applies each brand to 20 volunteers, randomly assigning which arm gets which brand. She measures the percent of sunburn after exposure. What is the response variable?

Accepted Answer

The percent of sunburn on each arm

Question 6

Which of the following is a reason to use blocking in an experiment?

Accepted Answer

To account for identifiable sources of variability among experimental units.

Question 7

Suppose you conduct an experiment comparing two diets and find a difference in average weight loss between groups. Which of the following would indicate that this difference is statistically significant?

Accepted Answer

The difference is larger than what would be expected due to natural variability alone.

Question 8

In a survey, random selection is used to choose participants from a population. What is the main benefit of this approach?

Accepted Answer

It creates a representative sample, reducing sampling bias.

Question 9

Which of the following is TRUE about the difference between random selection and random assignment?

Accepted Answer

Random assignment is used in experiments to create similar groups, while random selection is used in surveys to obtain a representative sample.

Question 10

A researcher wants to generalize her experimental results to a larger population. Under which condition is this most appropriate?

Accepted Answer

If the sample was randomly selected from the population.

Question 11

Which of the following best describes a lurking variable?

Accepted Answer

A variable that is not included in the study but could affect the response variable.

Question 12

In a nail polish experiment, 30 artificial nails are randomly assigned to two colors and then exposed to chlorine. The percent of polish chipped is measured. Which principle is being used by using artificial nails instead of natural nails?

Accepted Answer

Control

Question 13

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

Accepted Answer

Elimination

Question 14

A boxplot comparison of two treatments shows that the medians are outside the typical values of each other. What does this suggest?

Accepted Answer

The difference is statistically significant.

Question 15

Which formula would you use to calculate the mean difference between two treatment groups?

Accepted Answer

$$	ext{Mean Difference} = \overline{X}_1 - \overline{X}_2$$

Question 16

Which of the following scenarios best illustrates the use of blocking?

Accepted Answer

Grouping subjects by a variable such as gender, then randomizing within each group.

Question 17

Why is it important to replicate an experiment on a different population?

Accepted Answer

To test whether the results hold under different conditions and populations.

Question 18

Which of the following is a key difference between an experiment and an observational study?

Accepted Answer

Experiments involve random assignment of treatments, while observational studies do not.

Question 19

If an experiment does not use random assignment, which of the following is TRUE?

Accepted Answer

It is not possible to make conclusions about causality.

Question 20

A researcher uses side-by-side boxplots to compare two treatments. What is the main purpose of this comparison?

Accepted Answer

To visually assess differences in the distribution and central tendency of the response variable between treatments.

Experiments and Observational Studies: Principles of Experimental Design

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