Logical ReasoningDifficulty: Medium

PT124 S1 Q13 Explanation

Some doctors believe that a certain

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

TopicsNecessary Assumption

Keep going in LSAT Lab

  • Save & drill this skill — build targeted practice sets from questions like this one

  • Video walkthroughs — watch every question solved step by step

  • 81 official LSATs — as questions, timed sections & full-length tests

Start practicing free

Free to start

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

Some doctors believe that a certain drug reduces the duration of episodes of vertigo, claiming that the average duration of vertigo for people who suffer from it has decreased since the drug was introduced. However, during a recent three-month shortage of the drug, there was no significant change in the the drug has no effect on the duration of vertigo.

What this question is testing

Necessary Assumption

Your task

Find the assumption the argument requires in order for its conclusion to hold.

Common trap

Answers that would help the argument but aren't strictly required (sufficient, not necessary).

Winning move

Negate each choice — the right one breaks the argument when negated.

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

The question
13.

Which one of the following is an assumption required by

Answer choices

  1. Correct80% picked this

    If a drug made a difference in the duration of vertigo, a three-month shortage of that drug would have caused a significant change

    Why this is right

    This restates the assumption E → CD in contrapositive form.

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

  2. Negated Logic5% picked this

    If there were any change in the average duration of vertigo since the introduction of the drug, it would have demonstrated that the drug

    This restates the assumption CD → E in a clever form of a contrapositive.

  3. Too Strong12% picked this

    A period of time greater than three months would not have been better to use in judging whether the drug has an

    Even if a period of time greater than three months would have been better to use, three months could still be enough time to make the determination satisfactorily.

  4. Weakens2% picked this

    Changes in diet and smoking habits are not responsible for any change in the average duration of vertigo since

    This makes it more likely that any change in the average duration of vertigo since the introduction of the drug is the result of the drug.

  5. Too Strong2% picked this

    There are various significant factors other than drugs that decrease the duration of vertigo for many people

    There need not be various significant factors other than the drug that could explain the decrease in the average duration of vertigo since the drug was introduced. One factor would be enough. Furthermore, it’s unknown whether the doctors who believe there has been a reduction in the average duration of vertigo are correct that such a reduction has occurred.

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill
LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free