Research
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AP Research — Cheatsheet

Formulas, exam-day tips, and key terms on one page.

On the exam

How to get a 5

Key terms

Research QuestionA clear, focused, concise, complex, and arguable question around which research is centered.
Gap in the LiteratureA missing piece of information in the existing body of research that your study aims to fill.
Quantitative ResearchResearch that deals with numbers, statistics, and objective measurements.
Qualitative ResearchResearch that deals with words, meanings, and subjective experiences (e.g., interviews, observations).
Mixed MethodsA research approach that combines both quantitative and qualitative methods.
MethodologyThe overarching rationale and theoretical framework for your research approach.
MethodThe specific tools or procedures used to collect and analyze data (e.g., survey, experiment).
Literature ReviewA comprehensive summary and synthesis of previous research on a topic.
IRB (Institutional Review Board)A committee that reviews research proposals to ensure ethical treatment of human subjects.
Informed ConsentEnsuring participants fully understand the risks, benefits, and procedures of a study before agreeing to participate.
ValidityThe extent to which a test or instrument measures what it is supposed to measure.
ReliabilityThe consistency or repeatability of a measure or study.
How do you choose between a qualitative, quantitative, and mixed-methods design?Let the question decide. "How do people experience or make sense of X" calls for qualitative data; "how much, how many, is there a difference or relationship" calls for quantitative; a question with both a prevalence part and a mechanism part calls for mixed methods.
What design is required to support a causal claim, and why?A true experiment: random assignment to a treatment and a comparison condition, with the outcome measured identically in both. Random assignment distributes pre-existing differences across groups, which is what rules out alternative explanations.
What is a quasi-experiment, and when is it used?A comparison of groups formed without random assignment — often intact classes or self-selected participants. It is used when randomization is impossible, and its central weakness is selection: group differences may predate the treatment.
What is content analysis?A systematic method for examining a body of text, images, or media using a defined coding scheme applied consistently to every item. Because the scheme is explicit, claims about patterns such as framing or representation become checkable and replicable.
Distinguish probability from non-probability sampling and name examples of each.Probability sampling gives every member of the frame a known chance of selection: simple random, stratified, cluster, systematic. Non-probability sampling does not: convenience, purposive, snowball, quota. Only probability samples support statistical generalization to the population.
What is stratified random sampling, and what does it accomplish?Dividing the population into meaningful subgroups (strata) and randomly sampling within each. It guarantees representation of every subgroup and generally reduces sampling error relative to a simple random sample of the same size.
What is a sampling frame, and what is coverage error?The frame is the actual list from which the sample is drawn. Coverage error occurs when the frame omits part of the target population — such as sampling town residents from a voter roll — so even a perfect random draw inherits the gap.
What are self-selection and nonresponse bias?Self-selection bias arises when participants choose whether to take part, so those with strong views or high engagement dominate. Nonresponse bias arises when those who do not respond differ systematically from those who do — which is why response rate must be reported.
How is qualitative sample size justified?By sufficiency rather than by a number: sampling continues until additional data stop yielding new themes, a point called saturation. The number, the recruitment strategy, and the variation sought must all be reported and defended.
What is the difference between reliability and validity?Reliability is consistency — the same measurement repeated gives the same result. Validity is accuracy — the instrument measures what it claims to. A scale that is always 5 pounds high is reliable but not valid; validity requires reliability but not the reverse.
Name and define three types of reliability.Test-retest: the same measure repeated over time gives consistent results. Inter-rater: independent coders or observers agree when applying the same scheme. Internal consistency (often Cronbach’s alpha): items on a scale behave as if measuring one construct.
What is internal validity, and what threatens it?The extent to which the study supports the claim that the treatment caused the outcome. Threats include confounding variables, selection differences between groups, history and maturation over the study period, testing or practice effects, and participant attrition.