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Epidemiologist: To evaluate the long-term safety of the new dietary supplement Novagen, researchers conducted a comprehensive five-year study. They tracked 5,000 individuals who consumed Novagen daily for the entire five-year period and compared them to a control group of 5,000 individuals who never consumed it. The researchers ensured both groups were strictly matched for age, diet, exercise habits, and initial cardiovascular health. The data shows that the individuals who consumed Novagen daily for five years had a 40 percent lower incidence of cardiovascular disease than the control group. This conclusively demonstrates that long-term, daily consumption of Novagen provides significant protection against cardiovascular disease.

Which of the following, if true, most seriously weakens the epidemiologist’s argument?

  1. A
    The individuals in the control group were significantly more likely than the Novagen group to regularly consume older, established medications that are known to have mild cardiovascular benefits.
  2. B
    It is practically impossible to find two groups of 5,000 individuals whose diet, age, and exercise habits match perfectly enough to isolate the effect of a single supplement.
  3. Individuals who develop any early signs of cardiovascular disease are universally instructed by their doctors to immediately cease taking all non-essential dietary supplements, including Novagen.Answer
  4. D
    A separate, large-scale study found no statistically significant difference in cardiovascular health between Novagen users and a control group after only six months of daily use.
  5. E
    Some individuals in the control group who did not take Novagen nevertheless had better cardiovascular health at the end of the study than some individuals who took Novagen daily.

Answer

The statement indicating that individuals are instructed to stop taking supplements if they develop early signs of cardiovascular disease.
The argument concludes that Novagen provides protection based on the lower incidence of disease in the group that completed the five-year regimen. However, if doctors instruct anyone showing early signs of the disease to stop taking the supplement, those individuals drop out of the experimental group. This creates a massive survivor bias: the group that successfully consumed the supplement for five years artificially excludes those who fell ill. This provides an alternative explanation for their lower disease rate and destroys the causal claim.

Step-by-Step Solution

1
Identify the conclusion and the supporting premises.
Conclusion: Novagen provides long-term protection against cardiovascular disease. Premise: A study showed a 40% lower disease incidence in people who consumed Novagen daily for 5 years compared to a strictly matched control group.
Deconstructing the argument's structure is the necessary first step to finding its logical vulnerabilities.
2
Analyze the logical gap between the premise and the conclusion.
The argument assumes that the correlation (taking Novagen for 5 years correlates with less disease) implies a specific causal direction (Novagen caused the health). It ignores the possibility of sample selection bias within the experimental group.
Identifying unstated assumptions reveals precisely how the argument can be weakened.
3
Evaluate the options to find one that exploits this gap by providing an alternative explanation.
The correct option reveals that people who get sick are told to stop taking the supplement, meaning they drop out of the '5-year daily user' group. This guarantees the final group will have an artificially low disease rate, regardless of the supplement's actual efficacy.
An alternate explanation for the premise's data effectively severs the causal link to the conclusion.

Key Concept

Identifying alternate causes and sample selection bias (Survivor Bias)
Estimated Time:2m 30s
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