q1 - showman

[ArchivalUser]

A recent study was conducted to evaluate the efficacy of
a new drug for preventing hospitalization from pneumonia
associated with HIV-positive people. After
obtaining the appropriate consents, researchers used
patient records of participating physicians to identify a
group of HIV-positive patients who received the drug
in the year preceding the observation period. A second
group of HIV-positive patients who had not received
the drug were also identified in these same records.
Both groups were followed for a 1-year period to determine
the number of hospitalizations and number of
deaths due to all causes. The number of hospitalizations
for the group given the drug was significantly lower
than for the group not given the drug. However, the
mortality rate from all causes was found to be significantly
higher in the group who received the drug.
Because of this differential mortality rate, the physician
conducting this study concluded that this drug should
not be given to HIV-positive patients. The conclusion is
most likely which of the following?
(A) Invalid because knowledge of whether the patient
had received the drug or not biased the measurement
of the outcome variable
(B) Invalid because of the presence of the Hawthorne
effect
© Invalid because physicians participating in the
study may not have been representative of all
physicians who treat HIV-positive patients
(D) Invalid because the patients who received the drug
may have been less healthy than those who did not
(E) Valid for the population under study

[ArchivalUser]

DDD

[ArchivalUser]

DD

[ArchivalUser]

_ DDD

[ArchivalUser]

The correct answer is D. The underlying problem with
this study is confounding. Specifically, it is likely that
the patients who received the drug were sicker than
those who did not. Note that decisions to give the drug
under investigation were made by physicians in the
course of their medical practice, not random assignment.
It seems very likely that the patients who received
the drug and those who did not were different in some
meaningful ways. One of the most likely differences is
disease severity. The higher mortality rate for those
patients who received the drug is consistent with this
interpretation. Note that we do not know if this issue of
disease severity is present, only that it is a possible (even
probable) alternative explanation for the findings.
For choice A to be correct, one would have to argue that
knowing that they received the drug made the patients
more likely to die, an unlikely scenario.
The Hawthorne effect (choice B) occurs when the fact
of measurement changes what is being observed. For
this to be the correct answer, one would have to argue
that knowing they were in the research study made
patients more likely to die, an unlikely scenario.
Because we are comparing the effect of treatment on
patients, and because the skill of the physician should
have little to do with the capacity to hand out medication,
the representativeness of the physicians (choice C)
is not germane.
Choice E is incorrect because the conclusion is likely
invalid. (See discussion of choice C.)