Why Should a Nurse Researcher Want to Limit or Eliminate

Why should a nurse researcher want to limit or eliminate extraneous variables in a study?

A) More research questions would be required to account for the extraneous variables.
B) Extensive statistical analysis would be required to justify the presence of extraneous variables.
C) Extraneous variables compete with the independent variables as explanations of the study's outcome.
D) Manipulation of the extraneous variables increases the risk for researcher bias in the study's outcomes.