A Researcher Is Wishing to Undertake a Study of the Relationship

A researcher is wishing to undertake a study of the relationship between a specific type of analgesia and levels of pain experienced by sufferers of rheumatoid arthritis. It is believed that level of physical activity will influence both of these variables and so it has been decided that the use of partial correlations will allow for this in the research. On which of the following should a correlation be performed?

A) Type of analgesia used and level of pain experienced, controlling for level of physical activity
B) Level of pain experienced and level of physical activity, controlling for type of analgesia used
C) Type of analgesia used and physical activity level, controlling for level of pain experienced
D) None of the above