Northeastern University Law Internal and External Validity Discussion

Internal validity and external validity are two important concepts in evaluation research. So far, we have spent more time discussing internal validity. Part of the reason for this is that we need to establish internal validity before trying to achieve some measure of external validity. This is best illustrated by a definition of external validity: the generalizability of internally valid results.

Drawing on the readings by Welsh and Farrington (2007) and Weisburd and Hinkle (2014), make the case for why we need to replicate (that is, to provide a measure of external validity of) programs that have demonstrated effectiveness in preventing crime. Think about the importance of external validity in the context of (1) scientific research and (2) public policy. Lastly, is there a situation where we should move ahead with expanding a crime prevention program to other cities or communities without having a measure of external validity? Remember, your opinions are important here!