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LSAT Logical Reasoning › Strengthen
A school principal argues that banning smartphones during class improved student attention. She notes that in the month after the ban, teachers recorded fewer instances of students being off-task, and the average score on weekly quizzes rose modestly. She also points out that most students complied with the ban because phones were collected at the start of each period. The principal concludes that the smartphone ban caused the improvement in attention and learning, and she recommends extending the ban to lunch and after-school study halls to further boost academic performance.
The school’s internet filters block many entertainment websites on school computers.
Teachers who enforced the phone ban most consistently reported the greatest reduction in off-task behavior.
Students who were already attentive before the ban generally remained attentive afterward.
In the month after the ban, the school did not introduce any new textbooks or change the curriculum.
Some parents support the ban because they think students spend too much time on social media.
Explanation
The principal argues that banning smartphones improved student attention, citing fewer off-task behaviors and higher quiz scores. The argument's vulnerability is not establishing that the phone ban specifically drove these improvements. Answer choice C strengthens the argument by showing a direct relationship: teachers who enforced the ban most consistently saw the greatest reduction in off-task behavior. This suggests the ban itself, rather than some other factor, caused the improvement. Choice A is tempting because it rules out curriculum changes, but it doesn't demonstrate that the phone ban was the active ingredient. Strong causal arguments require evidence that the intensity or consistency of the proposed cause correlates with the magnitude of the effect.
A tech team lead claims that switching to a new project-management app improved on-time completion of tasks. She notes that in the quarter after the switch, the percentage of tasks finished by their deadlines rose from 70% to 82%. She also reports that the app sends automatic reminders, and team members say they now notice deadlines earlier. Therefore, she concludes that the new app caused the improvement and that adopting it companywide will make projects more reliable. Since on-time completion improved right after the switch, she treats the app as the main reason.
The kinds of tasks the team worked on in that quarter were similar in complexity to those in the previous quarter.
In the same quarter, the team hired an additional experienced developer.
The new app has a cleaner interface than the old app and is easier to navigate.
Some other teams in the company prefer to track tasks using spreadsheets instead of apps.
The company’s clients were generally more responsive that quarter than in the previous quarter.
Explanation
The team lead argues that switching to a new project-management app improved on-time task completion from 70% to 82%. The argument's vulnerability is not accounting for changes in the types or difficulty of tasks that might affect completion rates. Answer choice C strengthens the argument by confirming that the tasks worked on were similar in complexity to those in the previous quarter, ruling out the possibility that easier tasks artificially inflated the completion rate. This makes the app change a more credible explanation. Choice A is tempting because it mentions hiring an experienced developer, but this would actually weaken the argument by providing an alternative explanation. When evaluating productivity improvements, ensure that workload difficulty remained constant.
A city council member argues that installing brighter streetlights in one neighborhood caused a sharp reduction in car break-ins there. She notes that break-ins fell by nearly half in the two months after the new lights were installed, while the number of residents remained about the same. From this, she concludes that brighter streetlights will reduce car break-ins citywide, so the city should fund similar lighting upgrades in every neighborhood. Because the timing of the drop lines up with the lighting change, she takes the lights to be the main reason for the improvement.
In the two months after the lights were installed, police patrol hours in that neighborhood did not increase.
Car break-ins also decreased slightly in a nearby neighborhood that did not receive new streetlights.
Most car break-ins in the neighborhood had previously occurred on poorly lit streets where the new lights were installed.
Several residents in other neighborhoods have requested brighter streetlights for years.
The new streetlights use less electricity than the older streetlights did.
Explanation
The council member argues that brighter streetlights caused the 50% reduction in car break-ins, concluding that citywide lighting upgrades will reduce crime. The argument's key weakness is assuming the lights were the only relevant change during that period. Answer choice A strengthens this causal claim by ruling out increased police presence as an alternative explanation—if patrol hours hadn't increased, then the lighting change becomes a more plausible cause of the crime reduction. Choice D is tempting because it mentions another neighborhood, but it actually weakens the argument by suggesting crime dropped elsewhere without new lights. To strengthen causal arguments, eliminate plausible alternative explanations that could account for the observed effect.
A small publisher concludes that redesigning book covers increased sales. She notes that after several titles received new, more modern covers, sales of those titles rose in the following month. She also points out that the books’ content did not change and that the new covers were featured more prominently on the publisher’s website. Therefore, she concludes that cover redesigns are an effective way to increase sales for books in general, and she recommends redesigning the covers of the rest of the catalog. Since sales rose soon after the redesigns and nothing else about the books changed, she attributes the increase mainly to the new covers.
Readers who bought the redesigned titles were more likely to mention the cover in reviews than were earlier buyers.
The redesigned covers used brighter colors and larger fonts than the older covers did.
Other publishers sometimes redesign covers when they release new editions of books.
The publisher also arranged for several of the redesigned titles to be discounted by major online retailers.
Comparable titles that were not redesigned did not experience a similar sales increase during the same month.
Explanation
The publisher concludes that redesigning book covers increased sales for several titles in the following month. The argument's vulnerability is not ruling out other factors that might have boosted sales during that period. Answer choice E strengthens the argument by showing that comparable titles that weren't redesigned didn't experience similar sales increases during the same month—providing a control group that isolates cover design as the causal factor. Choice B is tempting because it mentions retailer discounts, but this would actually weaken the argument by providing an alternative explanation for increased sales. Strengthen publishing arguments by comparing redesigned titles to similar unchanged titles during the same time period.
A technology manager concludes that switching to a four-day workweek will increase productivity. A small pilot team at the company worked four longer days for six weeks, and during that period the team completed more project tasks than it had in the prior six weeks. Team members also reported that having a three-day weekend helped them return to work more focused. The manager reasons that better rest leads to better concentration, and better concentration leads to faster work. Therefore, adopting a four-day workweek across the company will increase overall productivity.
During the pilot, the team temporarily paused participation in several nonessential meetings.
Other companies in the same industry have experimented with four-day workweeks.
In the pilot team, individual employees who reported feeling more rested also tended to complete more tasks.
Some employees at the company prefer to start work earlier in the morning than others do.
The pilot team’s tasks during the six-week trial were similar in type and difficulty to its tasks during the prior six weeks.
Explanation
The technology manager concludes that a companywide four-day workweek will boost productivity, supported by a pilot team's higher task completion and reports of better focus from rest. The argument's vulnerability is that the pilot period might not be comparable if tasks were easier, weakening the causal claim. Choice A addresses this by confirming similar task difficulty, making the completion increase more attributable to the schedule. Choice E might tempt by linking rest to tasks within the team, but it's narrower and doesn't ensure overall comparability. In pilot-based arguments, strengthen by validating evidence reliability, focusing on equivalence to support broader application.
Which one of the following, if true, provides the most support for the conclusion above?
In a randomized trial, participants assigned to drink green tea daily for two weeks reported better sleep than controls, with no other lifestyle changes allowed.
Caffeine affects individuals differently, so some people are more sensitive to it than others.
Some green tea drinkers also reported using sleep-tracking apps to improve their sleep.
Most of the blog's subscribers are middle-aged women.
Respondents who drank black tea daily did not report higher sleep quality than non-tea drinkers.
Explanation
A randomized trial with controls and restricted changes isolates green tea as the cause of improved sleep, directly strengthening the claim. B is suggestive but leaves confounds, while A, D, and E are irrelevant or introduce alternative explanations.
Which one of the following, if true, provides the most support for the conclusion above?
The central bank signaled it would keep interest rates low the following year.
Business leaders said they appreciated the predictability of the policy environment that year.
Firms just above the eligibility threshold for the credit did not change their investment plans, while similar firms just below the threshold exhibited a sharp, immediate increase in investment when the credit took effect.
Neighboring regions that did not adopt the credit experienced a similar increase in private investment during the same period.
Commodity prices rose slightly in several sectors later in the year.
Explanation
A threshold-based jump among eligible firms, with no change among ineligible but similar firms, isolates the effect of the credit. The other choices either suggest broader causes or are irrelevant to identifying causation (B, C, D, E).
Which one of the following, if true, provides the most support for the conclusion above?
Nerpazine has a different mechanism of action than common painkillers.
In a double-blind, placebo-controlled trial, participants assigned to Nerpazine had significantly fewer migraine days than those on placebo, with adherence verified and no concurrent therapy changes allowed.
Forum posts about worsening symptoms are less frequent than posts about improvement.
Physicians vary widely in how often they prescribe Nerpazine.
Some users report mild side effects when taking Nerpazine.
Explanation
A rigorous placebo-controlled trial with adherence verification and restricted co-interventions isolates Nerpazine as the cause of reduced migraines. A, C, D, and E do not address efficacy or introduce bias and are thus irrelevant to the causal claim.
Which one of the following, if true, most strengthens the argument?
Overall charitable giving in the city increased last year compared to the year before.
Many donors report that they appreciate personalized content in charitable appeals.
In a follow-up randomized test using the same donor segments and zip codes, adding a handwritten note increased response from 8 percent to 11 percent.
The handwritten notes were written by volunteers rather than staff.
Among those who responded to letters with notes, the average donation amount was slightly lower than among responders to standard letters.
Explanation
B controls for list quality by randomizing within the same segments and replicates the effect, supporting causation. A, C, D, and E are irrelevant to whether the notes caused the higher response rate.
Which one of the following, if true, most strengthens the argument?
The outlet mall is located outside city limits and advertises regionally.
Surveys found that most bus routes in the region experienced fewer delays that year.
Merchants on a residential side street reported stable sales during the same period.
Sales gains were concentrated among businesses on the previously parked-on blocks and were not observed on comparable blocks in neighboring towns that kept curbside parking.
Many retailers on the main street extended their store hours after the ban took effect.
Explanation
E ties the increase specifically to the affected blocks and rules out broader regional trends by comparison, reinforcing a causal link to the policy. The other choices are regional, confounded, or introduce alternative explanations.