External validity refers to the ability to generalize the findings of an experiment to other settings, populations, and times. For educational psychology, this ability is a vital one, because it indicates the extent to which various programs shown to improve learning in one (perhaps artificial) setting can be confidently expected to show similar improvements in other (real) classroom settings. Without high external validity, the program may not have its intended or presumed effect in the various populations of interest. This entry will describe external validity in detail, offer suggestions for increasing it, describe threats to it, and discuss the trade-off between external validity and internal validity.

When a new educational technique or program is being evaluated in an experimental trial, of necessity the evaluation involves, for ...