In an RCT, the most serious threat to internal validity typically is which of the following?

Question

A) Mortality
B) Selection
C) Maturation
D) History

Answer 1

A
Feedback:
Mortality is the threat that arises from attrition in groups being compared. If different kinds of people remain in the study in one group versus another, then these differences, rather than the independent variable, could account for group differences in outcomes. The selection threat reflects biases stemming from preexisting differences between groups. Selection bias is the most challenging threat to the internal validity of studies not using an experimental design (e.g., nonequivalent control group designs, case-control designs), but can be partially addressed using control mechanisms described in the previous section. The history threat is the occurrence of events concurrent with the independent variable that can affect the outcome. In RCTs, history is not typically a threat because external events are as likely to affect one randomized group as another. The maturation threat arises from processes occurring as a result of time (e.g., growth, fatigue) rather than the independent variable. One-group pretest-posttest designs are especially vulnerable to the maturation threat.