AP Stats Experimental Design 2

Question 1

A researcher wants to test whether a new fertilizer increases crop yield. She randomly assigns 40 plots to fertilizer and 40 plots to no fertilizer. What is the primary purpose of random assignment in this experiment?

Accepted Answer

To create equivalent groups and allow causal inference

Answer

Random assignment balances confounding variables across treatment groups, enabling valid causal conclusions.

Question 2

In a study on pain relief, neither patients nor doctors know who received the actual medication. This design feature is called:

Accepted Answer

Double-blind

Answer

Double-blind means both subjects and evaluators are unaware of treatment assignment, reducing bias from both sides.

Question 3

A school district tests a new math curriculum in 5 classrooms while 5 others use the old curriculum. Students were not randomly assigned to classrooms. This study is best described as:

Accepted Answer

An observational study

Answer

Without random assignment of subjects to treatments, the study is observational and cannot establish causation.

Question 4

Which of the following is an example of a lurking variable?

Accepted Answer

An unmeasured variable that affects both the explanatory and response variables

Answer

A lurking variable is not measured but influences both the explanatory and response variables, potentially confounding results.

Question 5

Researchers block by gender before randomly assigning participants to treatment groups. The main reason for blocking is to:

Accepted Answer

Reduce variation within treatment groups by accounting for a known source of variability

Answer

Blocking groups similar experimental units together so that variation due to the blocking variable does not obscure treatment effects.

AP Practice Test

AP Practice Test

AP Stats Experimental Design 2