These advances in transport helped drive settlement in the western regions of North America. They were also essential to the nation's industrialization. ... Busy transport links increased the growth of cities. The transportation system helped to build an industrial economy on a national scale.
External validity means that the results of the study can be generalized to other conditions, people, stimuli, and time.
Therefore, replication is essential in experimental research, meaning that studies are usually conducted with different subject populations or in different settings and then have the same results.
Thus, the conclusion of the researchers can be generalized to a larger population.
