You are investigating the impact of physical activity on the

You are investigating the impact of physical activity on the diagnosis of Alzheimer\'s disease, and your data suggest a protective effect. While presenting your findings, a colleague asks whether you have thought about confounding variables, such as factor X. Under which of the following conditions could this factor have confounded the association of physical activity and alzheimer\'s disease?

Factor X is associated with the physical activity measure and Alzheimer\'s disease.

Factor X is a risk factor for some other disease, but not Alzheimer\'s disease.

Factor X is part of the causal pathway by which physical activity affects Alzheimer\'s disease.

Factor X may have

Factor X has caused a lack of follow-up of test subjects.

Solution

c ) Factor X is part of the causal pathway by which physical activity affects Alzheimer\'s disease.