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

Multiple Choice

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