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The SAT’s study-design questions rarely ask you to calculate anything. They hand you a study and ask which conclusion is justified, and the answer turns on two decisions made before any data existed: who got into the study, and who got which treatment. Random sampling and random assignment sound like one idea. They are two independent switches, and each licenses a different conclusion.
Key takeaways
- Random sampling (who is in the study) lets you generalize to the population sampled.
- Random assignment (who gets the treatment) lets you conclude cause and effect.
- The switches are independent: a study can have both, either, or neither.
- On "which conclusion is best supported," eliminate every choice claiming more than the design earned.
Two switches, two permissions
Random sampling is about recruitment. Was every member of the population equally likely to end up in the study? If yes, the sample is a fair miniature, and results generalize to that population (with the precision described by the margin of error). If the participants were volunteers or one classroom, the results describe the participants and nobody else.
Random assignment is about treatment. Once people are in, did chance decide who got the treatment and who was the comparison group? If yes, the groups start out statistically alike, so a difference at the end points at the treatment: that’s an experiment, and causal language is earned. If people chose their own group, whatever made them choose rides along as a hidden variable, and the honest conclusion is an association. That’s an observational study.
The 2x2 of justified conclusions
| Random assignment | No random assignment | |
|---|---|---|
| Random sampling | Cause and effect, generalizable to the population | Association only, generalizable to the population |
| No random sampling | Cause and effect, for the participants only | Association only, for the participants only |
How the SAT words it
Correct answers about observational studies sound deliberately deflating: "there is an association," "students who exercise tend to sleep more," often with an explicit "but no cause-and-effect relationship can be established." That deflation is precision, and the SAT rewards it. Wrong answers smuggle in causes or improves, or quietly widen "the participants" into "all teenagers." So run the elimination: cross out every choice claiming causation without random assignment, then every choice generalizing without random sampling. The survivor is usually the humblest sentence on the screen.
Try one: pick the justified conclusion
Researchers recruited 200 adult volunteers and randomly assigned half to an eight-week meditation program; the rest continued their usual routines. At the end, the meditation group reported significantly lower stress than the comparison group.
Which conclusion is best supported by the study’s results?
Try one: design the study
A nutritionist wants to determine whether a new free-breakfast program causes improved attendance among students at a large high school.
Which study design would best allow the nutritionist to draw a cause-and-effect conclusion?
The trap
Pick the most satisfying conclusion, the one with "causes" and "all students," because the study suggests it.
The move
Pick the conclusion the design paid for. No random assignment, no "causes." No random sampling, no "all."
Drill study-design questions with a tutor that makes you name both switches before you touch the conclusions.
Practice statistical claims →Frequently asked questions
- What is the difference between random sampling and random assignment?
- Random sampling decides who gets into the study and controls whether results generalize to the population. Random assignment decides who gets the treatment within the study and controls whether you can conclude cause and effect. They are independent decisions.
- When can you conclude cause and effect on the SAT?
- Only when participants were randomly assigned to treatment and comparison groups, which makes the study an experiment. Without random assignment, the justified conclusion is an association, however striking the difference between groups.
- Why do correct SAT answers say "associated with" instead of "causes"?
- Because most studies in these questions are observational, and association is all that design can establish. The SAT offers stronger-sounding causal conclusions as traps; the deflating, carefully hedged sentence is usually the justified one.