Observational Studies

Observational studies are where researchers observe the effect of a risk factor, diagnostic test, treatment or other intervention without trying to change who is or isn't exposed to it.¹

Observational research examines predetermined treatments, interventions, and policies and their effects.

Observational studies may be forward-looking (cohort), backward-looking (case–control), or looking at simultaneous events (cross-sectional). Cohort studies generally provide stronger evidence than the other two designs.

1. Case Report

2. Case-Series

3. Case Control

4. Cross Sectional (Surveys)

5. Cohort Studies

typically conducted in either (1) within registries or (2) as subgroup analyses within randomized clinical trials.

Registries are generally created with a specific disease, treatment, or population of interest, and can occur within a specific institution, network of institutions, or geographic region within which clinically relevant outcomes are recorded.

Subgroup analyses within clinical trials include any subset for which patients are not randomly assigned. Because subgroups are not randomly assigned, subgroup analyses share all the strengths and weaknesses of conventional observational studies, such as confounding and multiple hypotheses testing, and provide a similar level of evidence.¹]

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Reference

https://systematicreviewsjournal.biomedcentral.com/articles/10.1186/s13643-019-1131-4