Logical ReasoningDifficulty: Easy

PT119 S3 Q3 Explanation

A recent study involved feeding

A free, expert breakdown of this official LSAT Logical Reasoning question.

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Full official LSAT questions are available through LawHub. This page provides LSAT Lab's explanation, strategy, and review tools without republishing the full official question.

Stimulus

A recent study involved feeding a high-salt diet to a rat colony. A few months after the experiment began, standard tests of the rats’ blood pressure revealed that about 25 percent of the colony had normal, healthy blood pressure, about 70 percent of the colony had high blood pressure, and 5 percent is that high-salt diets are linked to high blood pressure in rats.

What this question is testing

Evaluate

The Argument

Researchers fed rats a high-salt diet. A few months later, 75% of those rats had high blood pressure. The conclusion: salt is linked to high blood pressure in rats.

Evaluate

Notice what the argument is missing — a "before" picture. We only see the rats after the diet. What if 75% of them already had high blood pressure when the study began? Then the diet did not cause anything; we would just be observing what was already true.

It is like measuring the height of a group of basketball players, finding they are tall, and concluding that something they did made them tall. Maybe — but you would want to know how tall they were when you started.

Goal

The right question to ask is the one that gets us the baseline measurement.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
3.

The answer to which one of the following questions is most relevant to evaluating the

Answer choices

  1. Out of Scope10% picked this

    How much more salt than is contained in a rat’s normal diet was there in

    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.

  2. Out of Scope2% picked this

    Did the high blood pressure have any adverse health effects on those rats

    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.

  3. Out of Scope3% picked this

    What percentage of naturally occurring rat colonies feed on

    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.

  4. Correct86% picked this

    How many rats in the colony studied had abnormally high blood pressure before

    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.

  5. Out of Scope0% picked this

    Have other species of rodents been used in experiments of the

    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.

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