Radon is a radioactive gas that seeps into homes from the soil. It is thought to be a cause of lung cancer. A research team investigates this hypothesis. The members of the team gather large amounts of data on basement radon concentrations and lung cancer rates and conclude that the more radon there is in a home, the more likely are people living in the home to develop lung cancer. After the study is published, other researchers criticize it by asserting that the studied neighborhoods with higher radon concentrations also have a higher percentage of older people and a higher percentage of cigarette smokers than the low-radon neighborhoods. Both advanced age and cigarette smoking increase the risk of lung cancer. This criticism, if correct, shows that the radon study suffered from __________.

• A. a lack of replication
• B. an untestable hypothesis
• C. nonsystematic observation and analysis of data
• D. uncontrolled variables

Answer: (D)

Verified step by step guidance

1. Identify the main hypothesis of the study, which is that higher radon concentrations in homes are associated with an increased risk of lung cancer.
2. Understand the criticism: The study's findings may be confounded by other factors such as age and smoking, which are also known to increase lung cancer risk.
3. Recognize that the presence of these confounding factors (age and smoking) means that the study did not adequately control for all variables that could affect the outcome.
4. Define 'uncontrolled variables': These are factors that can influence the results of an experiment or study but are not accounted for or controlled by the researchers.
5. Conclude that the criticism highlights a flaw in the study's design, specifically that it suffered from uncontrolled variables, which could lead to incorrect conclusions about the relationship between radon exposure and lung cancer risk.