Correlational studies are observational studies that look at the relationships between two or more variables that are not controlled by the researcher. These studies can reveal if a relationship exists between variables, but are limited because they do not prove causation. They are often used for gathering information about a topic or in situations where performing an experiment is not possible.
Searching for correlational studies: Look for Methodology or Publication Types that use terms like cohort, case-control, descriptive, or observational, longitudinal study.
Intervention studies are experimental studies that test the effectiveness of a preventative or therapeutic measure.
Searching for intervention studies: Look for Methodology or Publication Types that use terms like clinical trial, randomised-controlled (RCT), experimental, quasi-experimental, treatment outcome study
In medical and nursing literature, a level of evidence may be assigned to a research article based on the quality of their methodological design, validity, and applicability to patient care.
Correlational studies might fall into Level IV or V on this chart, whereas intervention studies might fall into Levels II, III, or IV.
Adapted from Melnyk, B. M., & In Fineout-Overholt, E. (2011). Evidence-based practice in nursing & healthcare: A guide to best practice.