AP Psychology: Research Methods and Statistics

Foundations of Psychological Science

• Psychology: The study of how the mind works and why people act the way they do.

• Empirical Evidence: Facts learned by directly watching or testing things.

• Scientific Method: A step-by-step way to ask questions, test ideas, and find answers.

• Core Principles:

  • Hypothesis: A smart guess that you can test.

  • Falsifiable: An idea that can be proven wrong if the test fails.

  • Peer Review: When other experts check your science work to make sure it is good before it gets published.

  • Replication: Doing an experiment again in the exact same way to see if you get the same result.

  • Reliability: How consistent a test is every time you use it.

  • Validity: How well a test actually measures what it says it measures.

• Cognitive Biases:

  • Confirmation Bias: Only paying attention to things that agree with what you already think.

  • Hindsight Bias: Thinking "I knew it all along!" after something happens.

  • Overconfidence: Being too sure that you are right when you might be wrong.

Research Methods and Design

• Professional Standards: Rules created by science groups, like the APA, to make sure research is done fairly and safely.

• Data Types:

  • Quantitative Data: Information made of numbers that you can count or measure.

  • Qualitative Data: Information made of words, pictures, or descriptions.

• Non-Experimental Methods:

  • Naturalistic Observation: Watching people or animals in their normal lives without changing anything.

  • Case Study: Studying one person or small group very closely to learn a lot of detail.

  • Survey Technique: Asking a group of people a set of questions to learn about them.

  • Correlational Research: Seeing if two things are connected, though it cannot prove that one causes the other.

• Experimental Method:

  • The only type of science test that can prove one thing directly causes another thing to happen.

  • Independent Variable: The thing the scientist changes on purpose.

  • Dependent Variable: The thing that gets measured to see if it changed.

  • Confounding Variable: An unexpected thing that messes up the results.

  • Operational Definitions: Clear directions explaining exactly how something is measured.

• Experimental Controls:

  • Experimental Group: The group that gets the real test or treatment.

  • Control Group: The group that does not get the treatment, used as a comparison.

  • Random Sampling & Random Assignment: Picking and sorting people by chance so the groups start out fair and equal.

  • Blinding Techniques: Keeping test details secret from participants or researchers so expectations do not ruin the results.

Statistical Analysis

• Descriptive vs. Inferential Statistics:

  • Descriptive Statistics: Numbers used to summarize data from a study.

  • Inferential Statistics: Using data from a small group to guess what a larger group is like.

• Measures of Central Tendency:

  • Mean: The mathematical average of a set of numbers.

  • Median: The middle number when you line them up from smallest to largest.

  • Mode: The number that shows up most often.

• Measures of Variation & Distribution:

  • Range: The highest number minus the lowest number.

  • Standard Deviation: A measure showing how spread out numbers are from the average.

  • Normal Curve: A standard bell-shaped graph where $68\%$ of scores are within $1$ step ($\sigma$) of the middle, $95\%$ are within $2\sigma$, and $99.7\%$ are within $3\sigma$.

• Distributions:

  • Bimodal Distribution: A score graph that has two peaks instead of one.

  • Positive Skew: A graph pulled to the right by a few unusually high scores.

  • Negative Skew: A graph pulled to the left by a few unusually low scores.

• Correlation Coefficients:

  • A score ($r$) between $-1$ and $+1$ showing how closely two things are linked.

  • Numbers near $0$ mean no connection; numbers near $-1$ or $+1$ mean a strong connection.

• Advanced Statistical Concepts:

  • Statistical Significance: A way to show that results are real and did not just happen by luck.

  • Effect Sizes: A measure of how strong or big a change actually is.

  • Regression to the Mean: Extreme scores usually get closer to normal when tested a second time.

Research Ethics

• Institutional Review Boards (IRB): Review teams that make sure experiments treat people safely and fairly.

• Mandatory Guidelines:

  • Informed Consent: Adults agreeing to join a study after being told what will happen.

  • Informed Assent: Children agreeing to join a study.

  • Confidentiality: Keeping participant secrets and names private.

  • Debriefing: Explaining the full study to people after it is over.

  • Meta Analysis: Combining results from many past studies to find a big answer.