Experimental Design · Overview

Experimental Design

Experimental design questions ask how a study was built rather than what it found: which factor the researchers changed, what they measured, what they held constant, which trial is the control, why a step was included, and how the experiment could be changed to answer a new question. They come mostly with Research Summaries passages, the ones that describe Study 1, Study 2 and so on.

Nearly every answer is on the page; the rest needs only basic science, such as ice water being at 0 °C. The setup text says what was changed and what was kept the same, and the tables and graphs show the results with units. You need no advanced science, only a habit: read each step of a procedure as a choice made on purpose, and ask what it keeps fair.

How often it appears

ACT reports Science results in three categories. Scientific Investigation, which covers experimental tools, procedures and design and how to modify or extend an experiment, makes up about 18–32% of the section, roughly 7 to 13 of its 40 questions.

The Science section is optional: 40 questions in 40 minutes, about 60 seconds a question, with no calculator. Once you have mapped an experiment, design questions are often quick to answer, which buys time for the data-heavy ones.

The question you’ll see

Which new trial, compared with a trial already performed, would show the effect of water volume alone?

In this module

  1. Overview Paid
  2. Independent, dependent and controlled variables Paid
  3. Control groups and why they matter Paid
  4. Why was this step done? Tools and procedures Paid
  5. Designing the next trial Paid
  6. Precision, repeated trials and sources of error Paid
  7. Strategy summary Paid
  8. Mastery quiz Paid
  9. Pace check Paid