AP Psych Zero: What Makes a Study an Experiment?
A study finds that students who eat breakfast get higher grades. Can the researchers say that breakfast improves grades?
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AP Psych Zero: What Makes a Study an Experiment?
This episode closes a common AP Psychology research-methods gap: a study that finds two things together is not yet a study that shows one thing caused the other.
What you will learn
- How to separate the independent variable a researcher manipulates from the dependent variable a researcher measures.
- Why random assignment is the step that turns a comparison into an experiment.
- How random sampling and random assignment do two different jobs.
- What a control group and a placebo are for.
- How to spot a confounding variable, and how single-blind and double-blind procedures reduce bias.
- How to answer the exam item that asks what a researcher should have done to avoid confounding variables.
Learning map
The episode puts two studies of the same question side by side, a breakfast survey and a breakfast experiment, to show why the manipulated variable, the assignment procedure, and the comparison group decide what a study can claim. A worked scenario then sorts a classroom study into independent variable, dependent variable, control group, and double-blind scoring.
Study check
Answer these without replaying the final minute:
- In the breakfast comparison, which variable is manipulated and which one is measured?
- What does random assignment buy that random sampling does not?
- A doctor gives the first fifty patients a new medication and the remaining fifty a placebo. What should the doctor have done differently, and why?
- Why does a placebo have to look identical to the real treatment?
- A study uses a convenience sample from one class but assigns students to conditions by computer. What can the study claim, and what can it not?
- What does a double-blind procedure control for that a single-blind procedure leaves open?
A useful reading routine is: name the manipulated variable, name the measured variable, find out how participants were assigned, check what the comparison group experienced, and then ask what else could explain the difference.
Scope and sources
The College Board Course and Exam Description asks students to identify independent, dependent, and confounding variables in research scenarios, to identify the experimental and control groups and the purpose of assigning people to groups, and to determine whether a study used single-blind or double-blind procedures to control for confounding variables such as experimenter bias or social desirability bias. It states the boundary directly: a study that does not manipulate an independent variable, or does not randomly assign participants to groups, is not experimental. 1
The same document gives research methods and design an approximate twenty-five percent weighting of the multiple-choice section, and it prints the medication item and the multivitamin study used in this episode among its sample questions. The AP Psychology course page describes the science practices the course is built around. 2
This episode is a study aid. Use your teacher’s current materials and the current College Board framework for course-specific assignments and exam details.
References
- 1AP Psychology Course and Exam Description — College Board
apcentral.collegeboard.org
- 2AP Psychology Course — AP Central, College Board
apcentral.collegeboard.org
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