Imagine a hypothetical study using a nonequivalent comparison group designed to assess the effectiveness of an anti-drug, Just Say No, campaign. In this study students at school X receive a semester-long series of Just Say No lectures.
Students at school Y across town do not receive the intervention. Unfortunately, during the semester a student at school Y died after an accidental drug overdose. This incident may have influenced drug use at school Y (but not school X) and consequently make it impossible to interpret our research findings. Which of the following threats to internal validity is present in this study?
a. selection-instrumentation
b. selection-maturation
c. selection-history
d. selection-testing
Question 2
In the context of experimental design, double blind refers to the situation in which
a. neither the experimenter nor the participant knows which experimental treatment the participant is receiving. b. the experimenter randomly chooses which group and treatment sequence each participant is assigned to.
c. neither the data analyst nor the participant knows what hypothesis is being tested.
d. two investigators analyze the data independently, and both are kept unaware of the identity of all participants.
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