INTRODUCTION TO ECONOMETRICS II ECO 306 NOUN 36 downward-sloping straight line. A value of 0 indicates that there is no association between the observations on X and Y in the sample. Of course the fact that r = 0 does not necessarily imply that ρ = 0 or vice versa. That is 1 ( , ) 1 ( , ) 1
( , ) 1
( , ) 0
corr X Y corr X Y means perfect positive linear association corr X Y means perfect negative linear association corr X Y means no linear association Figures a) to (d) below give more graphical explanations