A major threat to validity to the posttest-only design with nonequivalent groups is:
A) History
B) Testing
C) Instrumentation
D) Differential selection

Question

Quizplus · Accepted Answer

Differential selection is a major threat to validity in posttest-only designs with nonequivalent groups because the groups may differ in important ways before the treatment, affecting the outcomes.

A Major Threat to Validity to the Posttest-Only Design with Nonequivalent