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What can one
say about the comparison of the likely usefulness of Drug
R and morphine from the above two graphs?
You
answered:
 Drug
R and morphine look about the same in their propensity to
relieve pain and cause sedation.
INCORRECT
The
data shows that Drug R, 10 mg, produces moderately more
pain relief and sedation than morphine 7.5 mg. Although
this creates a visual impression that they have similar
therapeutic ratios, we cannot conclude that. With only one
dose tested, there is no information about the shape of
the dose-response curve for either analgesia or sedation
for either drug. If the dose response curves for the two
effects have different shapes or slopes, it may be that
a lower dose of Drug R that matches the analgesia of morphine
7.5 mg is still more sedating.
For
this reason, comparisons involving only a single dose of
each of two treatments are unlikely to provide convincing
evidence about their relative merits.
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