______ type threat to internal validity occurs when the experimental and control groups are selected based on different criteria or when participants are assigned to groups differentially and not by random assignment.
A) Attrition
B) Differential selection
C) Maturation
D) History

Question

Quizplus · Accepted Answer

Differential selection threatens internal validity because it introduces systematic differences between groups before the manipulation even begins, making it unclear whether any observed differences between the groups are due to the manipulation or to preexisting differences between them. The other options (attrition, maturation, and history) all refer to threats that occur after the groups have been selected and the manipulation has begun.

______ Type Threat to Internal Validity Occurs When the Experimental