The Nurse Is Using the Large Cohort Studies from Nurses

The nurse is using the large cohort studies from Nurses Health Studies and the Framingham Heart Study to support a report on the causalities of cardiovascular disease. Which factor causes doubt about the use of these studies in this manner?

A) Researchers reported associations among variables and not causality.
B) Researchers determined one or more variables caused a specific health outcome.
C) Researchers used an appropriate research design to support statements of causality.
D) Researchers performed additional studies to replicate the findings of the original studies.