Evaluations can take many forms and occur at different stage of a program, including:
Learn more at Sage Research Methods Online
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.
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
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.

Cochrane Library is a collection of databases that contain different types of evidence to inform healthcare decision-making. This collection also provides information about Cochrane groups.
Annual Reviews Online provides research literature in various disciplines within the Biomedical, Physical, and Social Sciences.
PQDT Global offers millions of works from thousands of universities. Full-text coverage spans from 1743 to the present, with citation coverage dating back to 1637.