Correlational vs experimental: claims and validities
Every question in both studies depends on one prior judgement: did the researcher manipulate anything or only measure? Get that wrong and the rest of the answers are wrong in a consistent, easily-spotted way.
Editorial process
Last reviewed · August 15, 2026
Design first, then everything follows
One question decides all the others, so answer it first for each study: did the researcher manipulate a variable, or only measure what was already there? Study 1 measures both self-esteem and income and looks at how they move together, so it is correlational. There is no independent variable to name, which is why the second question forks — for a correlational study you report the direction of the association, and here it is positive, since self-esteem scores rose as income rose. Study 2 randomly assigns participants to Kombucha or a taste-matched placebo, and random assignment is manipulation, so it is an experiment. The independent variable is the beverage received and the dependent variable is whatever was measured afterwards. Note that two groups alone would not settle it — it is the random assignment that makes the design experimental, and a study comparing drinkers who chose Kombucha with those who did not would still be correlational.
The causal question in Study 1 has a firm answer and three named reasons. No, income cannot be said to cause higher self-esteem, because the design meets only one of the three requirements for a causal claim. Covariance is satisfied — the variables do move together. Temporal precedence is not: nothing establishes that income came first, and higher self-esteem plausibly leads to behaviour that raises income. Internal validity is not: any number of third variables, including education, occupational status, health and family background, could produce the association without either variable touching the other. Name those three requirements explicitly rather than saying correlation is not causation, because the chapter's framework is what is being examined. For Study 2, note what the double-blinding buys: neither participants nor assistants knew the allocation, which controls expectancy on both sides and is exactly what strengthens internal validity controls expectancy on both sides, and that is exactly what strengthens internal validity here.
Likely learning objectives
Inferred from the brief — check these against your own rubric.
- 01Classify a study by whether a variable was manipulated or merely measured.
- 02Report association direction for a correlational design and variables for an experimental one.
- 03Apply the three requirements for a causal claim to a specific study.
- 04Explain what double-blinding controls and which validity it strengthens.
Read the full question
Review every instruction before using the planning guidance that follows.
Course-wide instructions that accompany this question
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Turn the brief into deliverables
- 01A design classification for each study, with the reason.
- 02Direction of association or named variables, as appropriate to each design.
- 03A reasoned answer on causation using the three causal criteria.
- 04Correct use of the chapter's terminology.
Classify, identify variables, then judge causation
Classify Study 1
Identify it as correlational and say why measurement without manipulation makes it so.
Direction of the association
State that the association is positive and describe it in the study's own terms.
The causal question
Apply covariance, temporal precedence and internal validity to the income and self-esteem claim.
Classify Study 2
Identify it as an experiment and name the independent and dependent variables.
What blinding controls
Explain what double-blinding removes and which validity that protects.
Where the four validities are defined
Recommended databases
- Chapter 3 of your course text
- Office of Research Integrity education materials
- NCBI Bookshelf
- PubMed Central
Search sequence
- 1.Fix the chapter's own definitions of the three claims and four validities before answering, since the marking follows them.
- 2.Check the standard statement of the three causal criteria so you name them rather than paraphrase.
- 3.Look up a worked example of a third-variable problem to make the Study 1 answer concrete.
- 4.Confirm what single-blind and double-blind each control, since the distinction carries the last answer.
Reference shortlist
These are authoritative starting points, not a ready-made bibliography. A qualified reviewer must confirm that each source fits the assignment and supports the claim beside which it is cited.
Nothing here is cleared for citation until you have read it.
- 01
Research Design: Descriptive Studies
Office of Research Integrity, U.S. Department of Health and Human Services · 2024
Sets out descriptive and correlational designs and their limits, which is the framework the first study is judged against.
- 02
Human Subjects Research Design
StatPearls, NCBI Bookshelf · 2023
Covers design choice and the control that random assignment provides, the deciding feature in the second study.
- 03
Evidence-Based Medicine
StatPearls, NCBI Bookshelf · 2024
Places these designs in an evidence hierarchy, useful for explaining why the causal claim needs more than covariance.
- 04
Research Ethics
StatPearls, NCBI Bookshelf · 2023
Relevant to the placebo arm in the second study, where deception and consent both come into play.
Review before submission
Common mistakes
- Calling Study 1 an experiment because it has two variables.
- Naming an independent variable in a correlational study, where there is none.
- Answering the causal question with 'correlation is not causation' and no criteria.
- Missing that random assignment, not the presence of two groups, is what makes a study experimental.
- Overlooking the double-blinding in Study 2, which is the detail the design turns on.
Submission checklist
- Did you decide manipulation versus measurement before anything else?
- Is the direction of association stated for the correlational study?
- Are the independent and dependent variables named for the experiment?
- Do you name all three causal criteria and say which fail?
- Have you said what the double-blinding controls?
Use this guide to plan and review your own work. Follow your institution's rules and read our academic-integrity policy.
Written by
Aaron Bishop
MA, Education
assignment interpretation and research-methods coaching across disciplines
Aaron leads the EssayCrackers editorial desk. He works on how assignment briefs are read — what a rubric is actually asking for, and where students most often answer a different question than the one set.
Reviewed by
Dr. Nathan Cole
PhD, Rhetoric & Composition
Argumentation and thesis development
Nathan teaches first-year composition and directs a university writing center. He reviews EssayCrackers guides for argumentative soundness and citation accuracy.