Match the Research Examples in 1-7 with the Main Threat

Multiple Choice

Match the research examples in 1-7 with the main threat to internal validity that it contains (a-g) .
-A psychiatrist selects a group of patients with the most extreme symptoms of depression. After one month of therapy, the patients have markedly improved.

A) Maturation
B) History or environmental events
C) Repeated testing
D) Instrumentation
E) Selection or assignment
F) Mortality or attrition
G) Statistical regression