Curriculum fit: US AP Psychology. Research methods and design is about 25% of the multiple-choice questions and data interpretation about 10%, according to the AP Central course page checked on 6 November 2026.
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What Is It?
Psychology is a science, so the exam keeps asking how a study was designed and what its results can show. Research methods and design is about 25% of the multiple-choice questions, and data interpretation about 10%.
In an experiment, researchers change the independent variable (IV), measure the dependent variable (DV), and use random assignment to put participants into groups. This is the only method that can show cause and effect.
A correlation shows how two variables move together, from −1 to +1. A strong correlation does not prove one thing causes the other.
Key Formulas and Ideas
- Independent variable (IV) = what the researcher changes. Dependent variable (DV) = what is measured.
- Random assignment (who goes into which group) allows cause-and-effect conclusions. Random sampling (who is chosen from the population) allows generalising.
- Correlation coefficient r runs from −1 to +1. Close to ±1 is strong, close to 0 is weak. The sign gives the direction.
- Normal curve: about 68% of scores within 1 standard deviation of the mean, about 95% within 2, and about 99.7% within 3.
- Ethics: informed consent, protection from harm, confidentiality and debriefing.
Worked Examples
Find the IV and DV
Researchers give one group caffeine and another group a placebo, then measure reaction time. Name the IV, DV and control group.
- The researchers choose caffeine or placebo, so the IV is the drug condition.
- Reaction time is measured, so it is the DV.
- The group with the placebo is the control group.
✓ Answer IV: caffeine or placebo. DV: reaction time. Control: the placebo group.
Read a Correlation
A study finds r = −0.80 between hours of social media and hours of sleep. Describe the relationship.
- The sign is negative, so the variables move in opposite directions.
- 0.80 is close to 1, so it is strong.
- A correlation cannot show cause, so you cannot say social media causes less sleep.
✓ Answer A strong negative correlation, not proof of cause
Use the Normal Curve
IQ scores have a mean of 100 and a standard deviation of 15. About what percent of people score between 85 and 115?
- 85 and 115 are 1 standard deviation below and above the mean.
- About 68% of scores fall within 1 standard deviation.
- So about 68% score between 85 and 115.
✓ Answer About 68%
Common Mistakes to Avoid
- Saying a correlation shows cause. Only a well-controlled experiment can do that.
- Mixing up random sampling and random assignment.
- Calling the thing the researcher changes the dependent variable.
- Thinking a negative correlation is weak. A correlation of −0.9 is very strong.
- Forgetting to define the variables with specific, measurable details (an operational definition).
Practice Questions
Frequently Asked Questions
What is the difference between random sampling and random assignment?
Random sampling is how participants are picked from a population, which helps the results apply to that population. Random assignment is how participants in the study are placed into groups, which helps show cause and effect.
What does statistically significant mean?
It means the result is unlikely to be due to chance alone. In psychology a probability (p) value below .05 is the usual cut-off, though this does not tell you how big or important the effect is.
Why does the exam test ethics?
Studies on people must protect them. AP Psychology expects you to know ideas such as informed consent, confidentiality, protection from harm and debriefing, and to apply them to an example study.
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Reviewed by StudyMorrow editorial review on 6 Nov 2026.