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Experimental Design Flashcards

7 cards from real AP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Experimental Design flashcards as text

  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?

    Answer: To create equivalent groups and allow causal inference

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

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

    Answer: Double-blind

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

  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:

    Answer: An observational study

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

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

    Answer: An unmeasured variable that affects both the explanatory and response variables

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

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

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

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

  6. In a completely randomized design with three treatments, 60 subjects are randomly assigned so that each treatment group has 20 subjects. What is the key advantage of this design over a block design?

    Answer: It is simpler to implement when no major sources of variation are known

    A completely randomized design is appropriate and simpler when no important blocking variables are identified.

  7. A researcher uses a table of random digits to assign subjects to treatment groups. Subject 1 gets the first digit, subject 2 gets the second, etc., assigning odd digits to Treatment A and even digits to Treatment B. This procedure ensures:

    Answer: Random assignment to treatments

    Using a random digit table to assign subjects to treatments is a valid method of random assignment in an experiment.