This article reviews the origins and use of the terms quasi-experiment and natural experiment. It demonstrates how the terms conflate whether variation in the independent variable of interest falls short of random with whether researchers find, rather than intervene to create, that variation. Using the lens of assignment--the process driving…

The What Works Clearinghouse (WWC) identifies existing research on educational interventions, assesses the quality of the research, and summarizes and disseminates the evidence from studies that meet WWC standards. The WWC aims to provide enough information so educators can use the research to make informed decisions in their settings. This…

This issue of "FOCUS" discusses external validity and what rehabilitation researchers can do to help practitioners answer the question "How far can we generalize this finding-- is it applicable to other clients/patients, with different characteristics, in dissimilar settings treated by other clinicians?," which clinicians and…