Suppose that an investigator tested the treatment and no-treatment groups at very different times and in different places. In addition to the typical threats to the two-group design, the investigator would have to worry about ____, a threat to internal validity that usually doesn't trouble researchers who use a two-group design.
A) instrumentation
B) selection
C) regression
D) history

Question

Quizplus · Accepted Answer

When testing groups at different times and places, external events or changes in the environment (history) could affect the results, posing a threat to internal validity.

Suppose That an Investigator Tested the Treatment and No-Treatment Groups