Which of the Following Situations Represents a Threat to Internal

Which of the following situations represents a threat to internal validity in an experimental study measuring the effect of audio-taped instructions to patients being discharged home after coronary artery bypass graft surgery?

A) Both men and women were included as subjects in the study.
B) Two new surgeons recently began performing the coronary artery bypass graft surgeries.
C) Patients in the experimental group passed their tapes on to those in the control group receiving usual care.
D) Data collection took 1 year.

Correct Answer:

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