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Old 02-06-2012
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Default conclusion is most likely invalid because of which of the following?

Q. A recent study was conducted to evaluate the efficacy of a new drug for preventing hospitalization from pneumonia associated with HIV-infection. Reducing hospital stays dramatically lowers the cost of medical care. One group of patients, who received the drug in the year preceding the observation period, was identified from patient records of participating physicians. A second group of patients who had not received the drug was also identified from the records of these same physicians. Both groups were followed for a three-year period to determine the number of hospitalizations, and any deaths from all causes. The number of hospitalizations for the group given the new drug was significantly lower (p ś .001) than for the group not given the new drug. However, the mortality rate from all causes was found to be significantly higher (p ś .01) in the group who received the drug. Based on these results, the physicians conducting the study decided that patients should not be given the drug. This conclusion is most likely invalid because of which of the following?
A. Incorrect classification of patients into the appropriate research arm
B. Knowledge about whether patients had taken the drug or not biased the measurement of the outcome variables
C. Patients who received the new drug may be less healthy than those who did not
D. Physicians who participated in the study may not be representative of the universe of physicians at large
E. The existence of a Hawthorne effect
F. The sickest HIV patients died before they could be enrolled in the study
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Ans .........C...........
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Old 02-08-2012
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The answer is C.
Because all patients enrolled in the study came from the records of the same physicians, whether or not the patients received the new drug depended on the assessment and treatment decisions made by each physician. It is very likely that those patients to whom the physicians administered the new drug were different than those for whom they prescribed some alternative. One likely difference is that patients who received the new drug were ˇ°sicker,ˇ± and that this alone caused the physicians to use the new drug. The higher mortality rate in the group who received the drug supports this possibility. Failing to control for disease severity for patients in different treatment arms of a study is a major confounding element in this type of research. Although it is possible that physicians record contained errors as to whether patients had received the new drug or not, this type of misclassification is (choice A) very unlikely.
For choice B to be true, one would need to argue that knowing which arm of the study a patient was in made them more likely to go to the hospital or to die. The outcome variables used here are clean, easily measured, and unlikely to be changed due to knowledge of which study group the patients were in.
Choice D is incorrect. It is almost certain that the physicians who participated in this study do not reflect all physicians everywhere. But, because both treatment and control subjects come from the same patient pool, using selected physicians does not bias the comparison that is at the core of the study design.
The Hawthorne effect (choice E) tells us that people act differently when they know they are being watched or measured. As noted in the comment on choice B, this is unlikely in this case.
In addition, having a control group, as in this case, offers a simple solution to the Hawthorne effect. Participants in both the treatment and the control group know they are being watched, so this factor will not contaminate any comparison between the two groups.
Choice F would be true for both the treatment and the control groups, and so does not disturb any research conclusion drawn by a comparison between them.
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