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Data collection methods and study design — ACT practice questions

Data collection methods and study design on the ACT Mathematics test covers how studies are set up, especially confounding and random assignment, and what those choices let you conclude. Students must spot when a treatment is mixed with another factor, such as a work shift changing along with a training program, and explain why randomly assigning similar units to treatments, like seedlings to light conditions or plots to fertilizers, makes groups comparable. Items typically give a short study and ask which factor is confounded or why randomization strengthens a comparison. Choices often confuse random assignment with random sampling or treat randomization as a guarantee of identical results.

  • Section: Mathematics 45 questions on the paper
  • 40 practice questions in the app

Sample questions

Question 1

Marcus measures soil quality in 72 greenhouse plots, then randomly assigns fertilizer A or B. Which of the following best explains why the fertilizers are assigned at random?

  1. AIt is required in order to measure each plot's soil quality.
  2. BIt lets the results generalize to every farm without random sampling.
  3. CIt tends to balance soil quality between the fertilizer groups.
  4. DIt makes the 72 plots a random sample of all farms.
Show answer

Answer: C — It tends to balance soil quality between the fertilizer groups.

Random assignment tends to distribute soil quality and other lurking factors across the fertilizer groups. This makes the groups more comparable before outcomes are measured.

Question 2

Anika randomly assigns 120 similar seedlings to either constant light or alternating light and darkness. Why does random assignment strengthen a comparison of their growth after 4 weeks?

  1. AIt makes every seedling grow at the same rate
  2. BIt ensures exactly equal initial average heights in both groups
  3. CIt tends to balance other growth-related variables between groups
  4. DIt permits the results to represent every plant species
Show answer

Answer: C — It tends to balance other growth-related variables between groups

Random assignment tends to distribute lurking variables, such as initial health, across treatment groups. This makes a difference in growth more plausibly attributable to the light condition.

Question 3

At a factory, morning-shift workers receive a new training program, and evening-shift workers receive the old training program. The morning group produces 14 more units per day. Which of the following factors is confounded with the training program?

  1. AUnits produced per day
  2. BWork shift
  3. CThe new training program
  4. DNumber of workers
Show answer

Answer: B — Work shift

Every worker receiving the new program is on the morning shift, and every worker receiving the old program is on the evening shift. The effects of shift and training cannot be separated.

Practice 40 Data collection methods and study design questions in the app

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