Which situation represents a threat to internal validity in an experimental study measuring the effect of a videotape of discharge instructions for patients who underwent coronary artery bypass graft (CABG) surgery?
A) Both men and women undergoing CABG surgery were included as subjects in the study.
B) Two new surgeons began performing CABG surgery during the study period.
C) Patients in the experimental group discussed aspects of the videotape with patients in the control group.
D) Data collection for the videotape and control groups took 1 year.

Question

Quizplus · Accepted Answer

Option C represents a threat to internal validity called "contamination" or "diffusion of treatment" effect. It occurs when the treatment in one group (in this case, the videotape of discharge instructions) is inadvertently received by the participants in the other group (the control group). In this situation, patients in the experimental group discussed aspects of the videotape with patients in the control group, which could have influenced the outcomes and biased the results in favor of the experimental group. This would compromise the internal validity of the study, making it difficult to draw conclusions about the true effects of the treatment.
Options A and B do not represent a threat to internal validity. Including both men and women in the study (Option A) is not a threat to internal validity, but it could impact external validity (generalizability) if there are gender differences in the response to the treatment. Similarly, the fact that two new surgeons began performing CABG surgery during the study period (Option B) is not a threat to internal validity unless there are significant differences in the outcomes between the surgeries performed by the new surgeons and those performed by the original surgeons.
Option D represents a potential threat to external validity (generalizability) but not internal validity. The length of data collection in the videotape and control groups may affect the generalizability of the results if the outcomes change over time or if the study population changes during the data collection period. However, it does not affect the internal validity of the study or the validity of the causal inferences that can be drawn from it.

Which Situation Represents a Threat to Internal Validity in an Experimental