Logical Reasoning

PT119 · S3 · Q3 A recent study involved feeding

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A recent study involved feeding a high-salt diet to a rat colony.

Conclusion

High-salt diets are linked to high blood pressure in rats.

Evidence

After several months on a high-salt diet, 75% of the rats in the colony had high or extremely high blood pressure; only 25% had normal blood pressure.

Evaluate

The argument needs the rats to have started out with normal blood pressure. If 75% of them already had high blood pressure before the experiment began, the high-salt diet did not cause anything — the high blood pressure was there all along.

Goal

Find a question whose answer would tell us whether the high-salt diet actually changed anything — i.e., the rats' baseline blood pressure before the study.

3.

The answer to which one of the following questions is most relevant to evaluating the conclusion drawn above?

  1. How much more salt than

    Out of Scope

    Knowing exactly how much more salt the high-salt diet contained does not affect whether salt is linked to high blood pressure. The argument's gap is whether the rats already had high blood pressure beforehand, not the precise dosage. Either answer to this question leaves the central uncertainty untouched.

    10% picked this

  2. Did the high blood pressure

    Out of Scope

    The conclusion is about whether high-salt diets are linked to high blood pressure — not about whether high blood pressure has health consequences. Whether or not the rats suffered ill effects, the link between salt and blood pressure stands or falls based on the baseline question, not this one.

    1% picked this

  3. What percentage of naturally occurring

    Out of Scope

    What rats do in nature is not relevant to the controlled study at hand. The argument is about whether the experimental diet caused the observed blood pressure — knowing what wild rats eat does not address whether these lab rats already had high blood pressure before the experiment.

    3% picked this

  4. Correct

    How many rats in the

    Why this is right

    This is the question that decides the argument. If many of the rats already had high blood pressure before the high-salt diet began, then the post-diet measurement does not show any effect — they would have had high blood pressure no matter what they ate. If, on the other hand, the rats started with normal blood pressure and now most of them have high blood pressure, the diet really does seem to be doing something. The answer to this question makes or breaks the conclusion.

    Skill tested: Evaluate · how this choice captures the argument's function is the move to repeat next time.

    86% picked this

  5. Have other species of rodents

    Out of Scope

    The conclusion is about rats specifically. Whether other rodent species have been studied does not help us evaluate whether this rat study supports its conclusion. We need information about these rats — particularly their pre-study blood pressure.

    0% picked this

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