Questions: A large study used records from Canada's national health care system to compare the effectiveness of two ways to treat prostate disease. The two treatments are traditional surgery and a new method that does not require surgery. The records described many cases where doctors had chosen the method of treatment for their patients. The study found that patients treated by the new method were significantly more likely to die within 8 years. What flaw in this study makes it impossible to determine if the new method is more dangerous? Explain your reasoning.

Solution Steps

The study uses records from Canada's national health care system, where doctors chose the treatment method for their patients. This introduces a potential bias because the assignment of treatments was not randomized. Patients in worse initial conditions might have been more likely to receive the new treatment, which could skew the results.

Since the assignment of treatments was not random, the study cannot establish a causal relationship between the treatment method and patient outcomes. The observed difference in mortality rates could be due to the initial health conditions of the patients rather than the treatment itself.

The study does not mention a control group, which is essential for providing a baseline comparison. Without a control group, it is difficult to determine whether the observed outcomes are due to the treatment or other confounding factors.

Final Answer