Suppose that you correlate AGE with SBP (systolic blood pressure) and find a strong positive correlation. Next you compute a first order partial correlation between AGE and SBP controlling for WEIGHT (body weight).
a. what would you conclude if this partial r were almost exactly zero?
b. What would you conclude if this partial r were a little smaller than the zero order r between AGE and SBP, but still substantially larger than zero?
c. What would you conclude if the zero order r and the partial r for these variables were essentially identical?