LSAT (Law School Admission Test)Logical ReasoningMedium
City Official: Our new public transportation system, which includes expanded bus routes and a new light rail line, has been a success. Ridership has increased by 20% in the last year, proving that our investment has encouraged more people to use public transit. \n\nWhich of the following, if true, most seriously weakens the city official's conclusion?
- AThe city's population has grown by 25% in the last year.
- BGasoline prices have significantly increased over the last year, making driving more expensive.
- CSeveral major downtown events, attracting large crowds, were held over the past year.
- DThe new light rail line only serves a small portion of the city's residents.
Show answer & explanationAnswer & explanation
Correct answer: A. The city's population has grown by 25% in the last year.
The official concludes that the *system* encouraged more people to use transit based on a 20% increase in ridership. If the population grew by 25%, then the *proportion* of people using public transit actually decreased, or at best stayed the same relative to population growth. The absolute increase in ridership is misleading without considering the baseline population change.
Why the other options are wrong
- B. This provides an alternative cause for increased ridership, weakening the claim that the *new system* was the sole driver, but 'A' is stronger.
- C. This provides a temporary, non-systemic reason for increased ridership, weakening the claim of sustained encouragement.
- D. This only indicates a limited reach, not necessarily a failure to encourage ridership among those it serves.
Baseline Fallacy
Occurs when an argument draws conclusions based on a change in absolute numbers without considering the change in the baseline or overall context from which those numbers are drawn.
- Often involves percentages or raw counts.
- Fails to account for population growth or other contextual shifts.
- Can lead to misinterpretation of improvement or decline.
Memory trick: Always check the starting line before judging the race.