GMAT Focus EditionVerbal ReasoningEasy
A new fitness tracker claims to accurately measure calorie expenditure during exercise. A consumer review website tested the device on ten volunteers performing various exercises. The website concluded that the tracker was highly accurate because its readings were consistently within 5% of the volunteers' self-reported calorie burn. Which of the following, if true, most seriously undermines the website's conclusion?
- AThe website did not compare the tracker's readings to those of other commercially available fitness trackers.
- BSelf-reported calorie burn is notoriously inaccurate and often overestimates actual expenditure.
- CThe volunteers were all highly fit individuals, which might not represent the general population.
- DThe tracker's manufacturer provided the volunteers with free samples of the device.
Show answer & explanationAnswer & explanation
Correct answer: B. Self-reported calorie burn is notoriously inaccurate and often overestimates actual expenditure.
The website bases its conclusion of 'high accuracy' on a comparison to self-reported calorie burn. If self-reported data is known to be inaccurate (Option A), then comparing to it cannot establish the *tracker's* accuracy, thus undermining the conclusion.
Why the other options are wrong
- A. Comparing to other trackers would be useful for relative performance, but not strictly necessary to assess the *absolute accuracy* if a reliable benchmark were used.
- C. This points to a potential issue with generalizability, but doesn't undermine the accuracy claim *within the context of the study's volunteers*.
- D. This suggests potential bias, but doesn't directly undermine the accuracy of the measurements themselves or the comparison method.
Challenging Measurement Validity
Questioning the reliability or appropriateness of the method used to measure a key variable, thereby invalidating any conclusions drawn from those measurements.
- Focuses on the data collection process itself.
- Highlights flaws in the chosen benchmark or instrument.
- Directly impacts the soundness of the evidence presented.
Memory trick: If your ruler is bent, all your measurements will be wrong.