Research Design

What this unit covers

The topics below follow the published Research course framework for Unit 1. Research publishes no per-unit weighting, so there is no percentage to chase here.

Lessons in this unit

• Finding the Gap in the Literature14 min · 3 objectivesDefine a "gap in the literature" and explain why original research must address one · Distinguish a genuine research gap from a topic that is merely unfamiliar to the student · Formulate a focused research question that a gap justifies
• Choosing a Method: Qualitative, Quantitative & Mixed15 min · 3 objectivesDistinguish qualitative, quantitative, and mixed-methods approaches · Match a research method to the kind of question being asked · Explain why the question — not preference — should drive method selection
• Sampling, Validity & Reliability14 min · 3 objectivesDistinguish common sampling strategies and their effect on generalizability · Define validity and reliability and explain how they differ · Identify threats to validity and reliability in a proposed design

Every term in Unit 1

All 29 terms we publish for Research Design, with definitions. Reading them through is the fastest way to find the ones you cannot define — then drill those in cram mode until you can produce them without the prompt.

From gap to question

A gap is a specific thing the literature has not established. Your question should be answerable, and answering it should close some part of that gap — not merely add another study.

Four kinds of gap

Population not studied, method not applied, context not examined, or contradictory findings unresolved. Naming which kind yours is makes the introduction far stronger.

Feasibility check

Can you get the participants, the data, the instrument, the permission and the time? A well-designed study you cannot execute scores lower than a modest one you can.

Independent and dependent variables

The independent variable is manipulated or grouped; the dependent is measured. If nothing is manipulated, you have a predictor and an outcome, not an IV and a DV.

Operationalization in practice

Turn a construct into a measurable indicator: "engagement" becomes "minutes spent on task per session, recorded by the platform." The construct is the claim; the operationalization is the evidence.

Hypothesis vs research question

A hypothesis predicts a direction and belongs to quantitative work. Qualitative work poses a question and does not predict, and imposing a hypothesis on it is a design error.

Null and alternative hypotheses

The null states no effect or no difference; the alternative states there is one. Statistical tests evaluate the null, which is why results are phrased as rejecting or failing to reject it.

Directional vs non-directional hypothesis

A directional hypothesis predicts which way; non-directional predicts only that there is a difference. Choose before collecting data, never after seeing it.

Between-subjects vs within-subjects

Between compares different groups; within measures the same people more than once. Within needs fewer participants but introduces order and practice effects.

Counterbalancing

Varying the order of conditions across participants so order effects cancel out. The standard remedy for within-subjects designs.

Random assignment vs random selection

Random assignment supports causal claims by equalizing groups; random selection supports generalization by making the sample representative. They solve different problems and are constantly confused.

Control group and comparison group

A control group receives no treatment; a comparison group receives an alternative. Naming yours correctly matters because it determines what your result means.

Placebo and blinding

Single-blind hides condition from participants; double-blind hides it from researchers too. Blinding addresses expectancy effects, which are a threat to internal validity.

Correlational design

Measures relationships without manipulation. Appropriate when manipulation is impossible or unethical, and it can never on its own support a causal claim.

Cross-sectional vs longitudinal

Cross-sectional measures at one time and confounds age with cohort; longitudinal follows the same people and loses participants to attrition. Each trades one problem for another.

Case study design

Deep examination of a single case. Strong for generating hypotheses and describing mechanism; weak for generalization, and the paper must say so.

Ethnography and participant observation

Extended immersion in a setting. Produces context no survey can, and raises distinctive ethical questions about consent in a group setting.

Phenomenology and grounded theory

Phenomenology studies lived experience of a phenomenon; grounded theory builds theory from data through iterative coding. Naming your qualitative tradition is expected.

Action research

The researcher intervenes in their own setting to improve practice, then studies the result. Common and legitimate in AP Research, and it requires explicit acknowledgment of the researcher's dual role.

Secondary data analysis

Analyzing data collected by someone else. Fast and often high quality, but you inherit their operationalizations and their sampling decisions.

Systematic literature review as a method

A review can itself be the method if the search protocol, inclusion criteria and coding scheme are stated and reproducible. Otherwise it is background, not research.

Pilot study

A small run before the real one, to test the instrument and the procedure. Reporting what the pilot changed strengthens the methodology section considerably.

Aligning question, method and conclusion

The single most common structural failure is a causal conclusion from a correlational design. Check that the verb in your conclusion is licensed by your method.

Justifying the method

The paper must say why this method rather than the alternatives. "I chose a survey" is not a justification; "a survey reaches the sample size a correlational claim requires within the time available" is.

Scope and delimitation

Delimitations are boundaries you chose; limitations are constraints imposed on you. Confusing them makes a deliberate design decision look like a flaw.

Positionality statement

A statement of how your own background may shape the research. Expected in qualitative work and increasingly in mixed methods, and it strengthens rather than weakens credibility.

Registering your design in advance

Writing the analysis plan before collecting data prevents unconscious adjustment. It is also the clearest defense against a charge of fishing for results.

Inclusion and exclusion criteria

State who counts as eligible before recruiting. Deciding afterward, once you can see the data, invalidates the sample.

Feasible sample sizes for student work

Small samples are normal and acceptable if the conclusion is scaled to them. The error is not a small n; it is a large claim built on one.

What examiners penalize here

• The AP Research paper and rubric expect you to *situate* your study in existing scholarship and articulate the gap it addresses. Reviewers look for an explicit statement of what is missing and why your question fills it — a study with no articulated gap loses credit in the very first rubric row.
• The AP Research rubric rewards **alignment**: your method must clearly follow from your question, and your analysis from your method. State explicitly why your chosen approach fits the question — reviewers penalize a mismatch between what you asked and how you tried to answer it.
• The AP Research rubric expects you to name your sampling method and openly discuss threats to validity and reliability in your Limitations. Reviewers reward researchers who anticipate their own design’s weaknesses — hiding them reads as not understanding them.

Practice Research

Our practice bank is drawn from across the whole course rather than filtered to one unit, which is closer to how the exam asks anyway — it will not tell you which unit a question is testing.

Questions about this unit

All 4 units of AP Research

1. Unit 1 · Research Design
2. Unit 2 · Data Collection & Analysis
3. Unit 3 · Academic Paper
4. Unit 4 · Presentation & Defense