a type of research in which participants are assigned to treatment or control groups using methods other than random allocation. Group assignment may occur through self-selection, clinician or researcher judgment, participant preference, or administrative criteria. Because the assignment is not random, non-randomized studies are more prone to bias and confounding than randomized controlled trials, but they can still provide valuable evidence, especially when randomization is not feasible or ethical.
Abbreviation: NRS
Example
A hospital evaluates a new rehabilitation program for stroke patients. Patients who agree to participate in the new program form the intervention group, while those who choose usual care form the comparison group. Because participants were not randomly assigned, this is considered a non-randomized study.