Regression-Discontinuity design

Description

The regression-discontinuity design uses a cut-off selection method, for example where subjects are selected based on scoring above or below a certain value on a previous test.

C	O	X	O
C	O		O

The key aspect about this design is that the control group is made up of those who fall at the other side of the cut-off score. The sample is thus cut in two, with one group as control and the rest as the treatment group.

Example

A training module is designed to increase the visual-spatial ability of people with lower 'IQ'. A sample is selected and tested for IQ, with those scoring below 100 being allocated to the cut-off group.

A test for visual-spatial ability was then administered before the lower-IQ group was given the training. A post-test score showed that their ability had increased in this area.

Visual-spatial test, average score	Pre-test score	Post-test score
Those with IQ below 100 (the treatment group)	25	32
Those with IQ above 100 (the control group)	46	47

Discussion

This is a relatively unusual design that is very useful in specific situations.

In practice, if the cut-off selects only a small number, then the control group may also be constrained. In the same way, more subjects may be sought for the control group if the treatment group takes a significant majority.

The name 'regression discontinuity' arises because the assignment by score causes a discontinuity across this score boundary between pre-test and post-test and between treatment and control groups, as in the diagram below.

Quick links

Regression-Discontinuity design

Description

Example

Discussion

See also

Site Menu

You can buy books here

Quick links

Disciplines

Techniques

Principles

Explanations

Theories

And

Site Menu

Quick links

Disciplines

Techniques

Principles

Explanations

Theories

And