Several people criticized dr. gordon's classroom experiment on the effects of density of living conditions on aggression due to issues of external validity. this means problems with:

The correct answer to this is:

This is a problem called "Generalizability".

Generalizability refers to the extent in which researchers extend the findings and conclusions of this research of a sample to the population at large. In this case, Dr. Gordon was criticized since he was extending the classroom results to the community at large.