Evidence-appraisal glossary
Regression Discontinuity Design
A method used when a treatment is assigned by a cutoff on a continuous score, such as a lab value or an age. People just below and just above the threshold are treated as nearly identical, so comparing their outcomes isolates the treatment's effect near the cutoff.
Also called: RDD, regression discontinuity.
Regression discontinuity exploits an arbitrary dividing line. Because whether someone lands just above or just below the cutoff is close to random, the two sides are balanced on other characteristics, mimicking a small randomized trial at the boundary. The estimate applies to people near the threshold rather than to everyone, and it holds only if nobody can precisely manipulate their score to land on the favorable side.
Read the full Reading the Evidence blog.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.